diff --git a/MAINTAINERS b/MAINTAINERS
index 30aca4a..b68c015 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -5193,6 +5193,7 @@ F:	arch/x86/kernel/cpu/mshyperv.c
 F:	drivers/hid/hid-hyperv.c
 F:	drivers/hv/
 F:	drivers/input/serio/hyperv-keyboard.c
+F:	drivers/pci/host/pci-hyperv.c
 F:	drivers/net/hyperv/
 F:	drivers/scsi/storvsc_drv.c
 F:	drivers/video/fbdev/hyperv_fb.c
diff --git a/drivers/pci/Kconfig b/drivers/pci/Kconfig
index 73de4ef..54a5441 100644
--- a/drivers/pci/Kconfig
+++ b/drivers/pci/Kconfig
@@ -118,4 +118,11 @@ config PCI_LABEL
 	def_bool y if (DMI || ACPI)
 	select NLS
 
+config PCI_HYPERV
+        tristate "Hyper-V PCI Frontend"
+        depends on PCI && X86 && HYPERV && PCI_MSI && PCI_MSI_IRQ_DOMAIN && X86_64
+        help
+          The PCI device frontend driver allows the kernel to import arbitrary
+          PCI devices from a PCI backend to support PCI driver domains.
+
 source "drivers/pci/host/Kconfig"
diff --git a/drivers/pci/host/Makefile b/drivers/pci/host/Makefile
index 7b2f20c..152daf9 100644
--- a/drivers/pci/host/Makefile
+++ b/drivers/pci/host/Makefile
@@ -2,6 +2,7 @@ obj-$(CONFIG_PCIE_DW) += pcie-designware.o
 obj-$(CONFIG_PCI_DRA7XX) += pci-dra7xx.o
 obj-$(CONFIG_PCI_EXYNOS) += pci-exynos.o
 obj-$(CONFIG_PCI_IMX6) += pci-imx6.o
+obj-$(CONFIG_PCI_HYPERV) += pci-hyperv.o
 obj-$(CONFIG_PCI_MVEBU) += pci-mvebu.o
 obj-$(CONFIG_PCI_TEGRA) += pci-tegra.o
 obj-$(CONFIG_PCI_RCAR_GEN2) += pci-rcar-gen2.o
diff --git a/drivers/pci/host/pci-hyperv.c b/drivers/pci/host/pci-hyperv.c
new file mode 100644
index 0000000..ba1e4c2
--- /dev/null
+++ b/drivers/pci/host/pci-hyperv.c
@@ -0,0 +1,2359 @@
+/*
+ * Copyright (c) Microsoft Corporation.
+ *
+ * Author:
+ *   Jake Oshins <jakeo@microsoft.com>
+ *
+ * This driver acts as a paravirtual front-end for PCI Express root buses.
+ * When a PCI Express function (either an entire device or an SR-IOV
+ * Virtual Function) is being passed through to the VM, this driver exposes
+ * a new bus to the guest VM.  This is modeled as a root PCI bus because
+ * no bridges are being exposed to the VM.  In fact, with a "Generation 2"
+ * VM within Hyper-V, there may seem to be no PCI bus at all in the VM
+ * until a device as been exposed using this driver.
+ *
+ * Each root PCI bus has its own PCI domain, which is called "Segment" in
+ * the PCI Firmware Specifications.  Thus while each device passed through
+ * to the VM using this front-end will appear at "device 0", the domain will
+ * be unique.  Typically, each bus will have one PCI function on it, though
+ * this driver does support more than one.
+ *
+ * In order to map the interrupts from the device through to the guest VM,
+ * this driver also implements an IRQ Domain, which handles interrupts (either
+ * MSI or MSI-X) associated with the functions on the bus.  As interrupts are
+ * set up, torn down, or reaffined, this driver communicates with the
+ * underlying hypervisor to adjust the mappings in the I/O MMU so that each
+ * interrupt will be delivered to the correct virtual processor at the right
+ * vector.  This driver does not support level-triggered (line-based)
+ * interrupts, and will report that the Interrupt Line register in the
+ * function's configuration space is zero.
+ *
+ * The rest of this driver mostly maps PCI concepts onto underlying Hyper-V
+ * facilities.  For instance, the configuration space of a function exposed
+ * by Hyper-V is mapped into a single page of memory space, and the
+ * read and write handlers for config space must be aware of this mechanism.
+ * Similarly, device setup and teardown involves messages sent to and from
+ * the PCI back-end driver in Hyper-V.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 as published
+ * by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
+ * NON INFRINGEMENT.  See the GNU General Public License for more
+ * details.
+ *
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/pci.h>
+#include <linux/semaphore.h>
+#include <linux/irqdomain.h>
+#include <asm/irqdomain.h>
+#include <asm/apic.h>
+#include <linux/msi.h>
+#include <linux/hyperv.h>
+#include <asm/mshyperv.h>
+
+/*
+ * Protocol versions. The low word is the minor version, the high word the major
+ * version.
+ */
+
+#define PCI_MAKE_VERSION(major, minor) ((u32)(((major) << 16) | (major)))
+#define PCI_MAJOR_VERSION(version) ((u32)(version) >> 16)
+#define PCI_MINOR_VERSION(version) ((u32)(version) & 0xff)
+
+enum {
+	PCI_PROTOCOL_VERSION_1_1 = PCI_MAKE_VERSION(1, 1),
+	PCI_PROTOCOL_VERSION_CURRENT = PCI_PROTOCOL_VERSION_1_1
+};
+
+#define PCI_CONFIG_MMIO_LENGTH	0x2000
+#define CFG_PAGE_OFFSET 0x1000
+#define CFG_PAGE_SIZE (PCI_CONFIG_MMIO_LENGTH - CFG_PAGE_OFFSET)
+
+#define MAX_SUPPORTED_MSI_MESSAGES 0x400
+
+/*
+ * Message Types
+ */
+
+enum pci_message_type {
+	/*
+	 * Version 1.1
+	 */
+	PCI_MESSAGE_BASE                = 0x42490000,
+	PCI_BUS_RELATIONS               = PCI_MESSAGE_BASE + 0,
+	PCI_QUERY_BUS_RELATIONS         = PCI_MESSAGE_BASE + 1,
+	PCI_POWER_STATE_CHANGE          = PCI_MESSAGE_BASE + 4,
+	PCI_QUERY_RESOURCE_REQUIREMENTS = PCI_MESSAGE_BASE + 5,
+	PCI_QUERY_RESOURCE_RESOURCES    = PCI_MESSAGE_BASE + 6,
+	PCI_BUS_D0ENTRY                 = PCI_MESSAGE_BASE + 7,
+	PCI_BUS_D0EXIT                  = PCI_MESSAGE_BASE + 8,
+	PCI_READ_BLOCK                  = PCI_MESSAGE_BASE + 9,
+	PCI_WRITE_BLOCK                 = PCI_MESSAGE_BASE + 0xA,
+	PCI_EJECT                       = PCI_MESSAGE_BASE + 0xB,
+	PCI_QUERY_STOP                  = PCI_MESSAGE_BASE + 0xC,
+	PCI_REENABLE                    = PCI_MESSAGE_BASE + 0xD,
+	PCI_QUERY_STOP_FAILED           = PCI_MESSAGE_BASE + 0xE,
+	PCI_EJECTION_COMPLETE           = PCI_MESSAGE_BASE + 0xF,
+	PCI_RESOURCES_ASSIGNED          = PCI_MESSAGE_BASE + 0x10,
+	PCI_RESOURCES_RELEASED          = PCI_MESSAGE_BASE + 0x11,
+	PCI_INVALIDATE_BLOCK            = PCI_MESSAGE_BASE + 0x12,
+	PCI_QUERY_PROTOCOL_VERSION      = PCI_MESSAGE_BASE + 0x13,
+	PCI_CREATE_INTERRUPT_MESSAGE    = PCI_MESSAGE_BASE + 0x14,
+	PCI_DELETE_INTERRUPT_MESSAGE    = PCI_MESSAGE_BASE + 0x15,
+	PCI_MESSAGE_MAXIMUM
+};
+
+/*
+ * Structures defining the virtual PCI Express protocol.
+ */
+
+union pci_version {
+	struct {
+		u16 minor_version;
+		u16 major_version;
+	} parts;
+	u32 version;
+} __packed;
+
+/*
+ * Function numbers are 8-bits wide on Express, as interpreted through ARI,
+ * which is all this driver does.  This representation is the one used in
+ * Windows, which is what is expected when sending this back and forth with
+ * the Hyper-V parent partition.
+ */
+union win_slot_encoding {
+	struct {
+		u32	func:8;
+		u32	reserved:24;
+	} bits;
+	u32 slot;
+} __packed;
+
+/*
+ * Pretty much as defined in the PCI Specifications.
+ */
+struct pci_function_description {
+	u16	v_id;	/* vendor ID */
+	u16	d_id;	/* device ID */
+	u8	rev;
+	u8	prog_intf;
+	u8	subclass;
+	u8	base_class;
+	u32	subsystem_id;
+	union win_slot_encoding win_slot;
+	u32	ser;	/* serial number */
+} __packed;
+
+/**
+ * struct hv_msi_desc
+ * @vector:		IDT entry
+ * @delivery_mode:	As defined in Intel's Programmer's
+ *			Reference Manual, Volume 3, Chapter 8.
+ * @vector_count:	Number of contiguous entries in the
+ *			Interrupt Descriptor Table that are
+ *			occupied by this Message-Signaled
+ *			Interrupt. For "MSI", as first defined
+ *			in PCI 2.2, this can be between 1 and
+ *			32. For "MSI-X," as first defined in PCI
+ *			3.0, this must be 1, as each MSI-X table
+ *			entry would have its own descriptor.
+ * @reserved:		Empty space
+ * @cpu_mask:		All the target virtual processors.
+ */
+struct hv_msi_desc {
+	u8	vector;
+	u8	delivery_mode;
+	u16	vector_count;
+	u32	reserved;
+	u64	cpu_mask;
+} __packed;
+
+/**
+ * struct tran_int_desc
+ * @reserved:		unused, padding
+ * @vector_count:	same as in hv_msi_desc
+ * @data:		This is the "data payload" value that is
+ *			written by the device when it generates
+ *			a message-signaled interrupt, either MSI
+ *			or MSI-X.
+ * @address:		This is the address to which the data
+ *			payload is written on interrupt
+ *			generation.
+ */
+struct tran_int_desc {
+	u16	reserved;
+	u16	vector_count;
+	u32	data;
+	u64	address;
+} __packed;
+
+/*
+ * A generic message format for virtual PCI.
+ * Specific message formats are defined later in the file.
+ */
+
+struct pci_message {
+	u32 message_type;
+} __packed;
+
+struct pci_child_message {
+	u32 message_type;
+	union win_slot_encoding wslot;
+} __packed;
+
+struct pci_incoming_message {
+	struct vmpacket_descriptor hdr;
+	struct pci_message message_type;
+} __packed;
+
+struct pci_response {
+	struct vmpacket_descriptor hdr;
+	s32 status; /* negative values are failures*/
+} __packed;
+
+struct pci_packet {
+	void (*completion_func)(void *context, struct pci_response *resp,
+				int resp_packet_size);
+	void *compl_ctxt;
+	struct pci_message message;
+};
+
+/*
+ * Specific message types supporting the PCI protocol.
+ */
+
+/*
+ * Version negotiation message. Sent from the guest to the host.
+ * The guest is free to try different versions until the host
+ * accepts the version.
+ *
+ * pci_version: The protocol version requested.
+ * is_last_attempt: If TRUE, this is the last version guest will request.
+ * reservedz: Reserved field, set to zero.
+ */
+
+struct pci_version_request {
+	struct pci_message message_type;
+	enum pci_message_type protocol_version;
+} __packed;
+
+/*
+ * Bus D0 Entry.  This is sent from the guest to the host when the virtual
+ * bus (PCI Express port) is ready for action.
+ */
+
+struct pci_bus_d0_entry {
+	struct pci_message message_type;
+	u32 reserved;
+	u64 mmio_base;
+} __packed;
+
+struct pci_bus_relations {
+	struct pci_incoming_message incoming;
+	u32 device_count;
+	struct pci_function_description func[1];
+} __packed;
+
+struct pci_q_res_req_response {
+	struct vmpacket_descriptor hdr;
+	s32 status; /* negative values are failures*/
+	u32 probed_bar[6];
+} __packed;
+
+struct pci_set_power {
+	struct pci_message message_type;
+	union win_slot_encoding wslot;
+	u32 power_state; /* In Windows terms */
+	u32 reserved;
+} __packed;
+
+struct pci_set_power_response {
+	struct vmpacket_descriptor hdr;
+	s32 status; /* negative values are failures*/
+	union win_slot_encoding wslot;
+	u32 resultant_state;  /* In Windows terms */
+	u32 reserved;
+} __packed;
+
+struct pci_resources_assigned {
+	struct pci_message message_type;
+	union win_slot_encoding wslot;
+	u8 memory_range[0x14][6]; /* not used here */
+	u32 msi_descriptors;
+	u32 reserved[4];
+} __packed;
+
+struct pci_create_interrupt {
+	struct pci_message message_type;
+	union win_slot_encoding wslot;
+	struct hv_msi_desc int_desc;
+} __packed;
+
+struct pci_create_int_response {
+	struct pci_response response;
+	u32 reserved;
+	struct tran_int_desc int_desc;
+} __packed;
+
+struct pci_delete_interrupt {
+	struct pci_message message_type;
+	union win_slot_encoding wslot;
+	struct tran_int_desc int_desc;
+} __packed;
+
+struct pci_dev_incoming {
+	struct pci_incoming_message incoming;
+	union win_slot_encoding wslot;
+} __packed;
+
+struct pci_eject_response {
+	u32 message_type;
+	union win_slot_encoding wslot;
+	u32 status;
+} __packed;
+
+static int pci_ring_size = (4 * PAGE_SIZE);
+
+/*
+ * Definitions or interrupt steering hypercall.
+ */
+#define HV_PARTITION_ID_SELF		((u64)-1)
+#define HVCALL_RETARGET_INTERRUPT	0x7e
+
+struct retarget_msi_interrupt {
+	u64	partition_id; /* use "self" */
+	u64	device_id;
+	u32	source; /* 1 for MSI(-X) */
+	u32	reserved1;
+	u32	address;
+	u32	data;
+	u64	reserved2;
+	u32	vector;
+	u32	flags;
+	u64	vp_mask;
+} __packed;
+
+/*
+ * Driver specific state.
+ */
+
+enum hv_pcibus_state {
+	hv_pcibus_init = 0,
+	hv_pcibus_probed,
+	hv_pcibus_installed,
+	hv_pcibus_maximum
+};
+
+struct hv_pcibus_device {
+	struct pci_sysdata sysdata;
+	enum hv_pcibus_state state;
+	atomic_t remove_lock;
+	struct hv_device *hdev;
+	resource_size_t low_mmio_space;
+	resource_size_t high_mmio_space;
+	struct resource *mem_config;
+	struct resource *low_mmio_res;
+	struct resource *high_mmio_res;
+	struct completion *survey_event;
+	struct completion remove_event;
+	struct pci_bus *pci_bus;
+	spinlock_t config_lock; /* Avoids two threads writing index page */
+	spinlock_t device_list_lock; /* Protects lists below */
+	void __iomem *cfg_addr;
+
+	struct semaphore enum_sem;
+	struct list_head resources_for_children;
+
+	struct list_head children;
+	struct list_head dr_list;
+	struct work_struct wrk;
+
+	struct msi_domain_info msi_info;
+	struct msi_controller msi_chip;
+	struct irq_domain *irq_domain;
+};
+
+/*
+ * Tracks "Device Relations" messages from the host, which must be both
+ * processed in order and deferred so that they don't run in the context
+ * of the incoming packet callback.
+ */
+struct hv_dr_work {
+	struct work_struct wrk;
+	struct hv_pcibus_device *bus;
+};
+
+struct hv_dr_state {
+	struct list_head list_entry;
+	u32 device_count;
+	struct pci_function_description func[1];
+};
+
+enum hv_pcichild_state {
+	hv_pcichild_init = 0,
+	hv_pcichild_requirements,
+	hv_pcichild_resourced,
+	hv_pcichild_ejecting,
+	hv_pcichild_maximum
+};
+
+enum hv_pcidev_ref_reason {
+	hv_pcidev_ref_invalid = 0,
+	hv_pcidev_ref_initial,
+	hv_pcidev_ref_by_slot,
+	hv_pcidev_ref_packet,
+	hv_pcidev_ref_pnp,
+	hv_pcidev_ref_childlist,
+	hv_pcidev_irqdata,
+	hv_pcidev_ref_max
+};
+
+struct hv_pci_dev {
+	/* List protected by pci_rescan_remove_lock */
+	struct list_head list_entry;
+	atomic_t refs;
+	enum hv_pcichild_state state;
+	struct pci_function_description desc;
+	bool reported_missing;
+	struct hv_pcibus_device *hbus;
+	struct work_struct wrk;
+
+	/*
+	 * What would be observed if one wrote 0xFFFFFFFF to a BAR and then
+	 * read it back, for each of the BAR offsets within config space.
+	 */
+	u32 probed_bar[6];
+};
+
+struct hv_pci_compl {
+	struct completion host_event;
+	s32 completion_status;
+};
+
+/**
+ * hv_pci_generic_compl() - Invoked for a completion packet
+ * @context:		Set up by the sender of the packet.
+ * @resp:		The response packet
+ * @resp_packet_size:	Size in bytes of the packet
+ *
+ * This function is used to trigger an event and report status
+ * for any message for which the completion packet contains a
+ * status and nothing else.
+ */
+static
+void
+hv_pci_generic_compl(void *context, struct pci_response *resp,
+		     int resp_packet_size)
+{
+	struct hv_pci_compl *comp_pkt = context;
+
+	if (resp_packet_size >= offsetofend(struct pci_response, status))
+		comp_pkt->completion_status = resp->status;
+	complete(&comp_pkt->host_event);
+}
+
+static struct hv_pci_dev *get_pcichild_wslot(struct hv_pcibus_device *hbus,
+						u32 wslot);
+static void get_pcichild(struct hv_pci_dev *hv_pcidev,
+			 enum hv_pcidev_ref_reason reason);
+static void put_pcichild(struct hv_pci_dev *hv_pcidev,
+			 enum hv_pcidev_ref_reason reason);
+
+static void get_hvpcibus(struct hv_pcibus_device *hv_pcibus);
+static void put_hvpcibus(struct hv_pcibus_device *hv_pcibus);
+
+/**
+ * devfn_to_wslot() - Convert from Linux PCI slot to Windows
+ * @devfn:	The Linux representation of PCI slot
+ *
+ * Windows uses a slightly different representation of PCI slot.
+ *
+ * Return: The Windows representation
+ */
+static u32 devfn_to_wslot(int devfn)
+{
+	union win_slot_encoding wslot;
+
+	wslot.slot = 0;
+	wslot.bits.func = PCI_SLOT(devfn) | (PCI_FUNC(devfn) << 5);
+
+	return wslot.slot;
+}
+
+/**
+ * wslot_to_devfn() - Convert from Windows PCI slot to Linux
+ * @wslot:	The Windows representation of PCI slot
+ *
+ * Windows uses a slightly different representation of PCI slot.
+ *
+ * Return: The Linux representation
+ */
+static int wslot_to_devfn(u32 wslot)
+{
+	union win_slot_encoding slot_no;
+
+	slot_no.slot = wslot;
+	return PCI_DEVFN(0, slot_no.bits.func);
+}
+
+/*
+ * PCI Configuration Space for these root PCI buses is implemented as a pair
+ * of pages in memory-mapped I/O space.  Writing to the first page chooses
+ * the PCI function being written or read.  Once the first page has been
+ * written to, the following page maps in the entire configuration space of
+ * the function.
+ */
+
+/**
+ * _hv_pcifront_read_config() - Internal PCI config read
+ * @hpdev:	The PCI driver's representation of the device
+ * @where:	Offset within config space
+ * @size:	Size of the transfer
+ * @val:	Pointer to the buffer receiving the data
+ */
+static void _hv_pcifront_read_config(struct hv_pci_dev *hpdev, int where,
+				     int size, u32 *val)
+{
+	unsigned long flags;
+	void __iomem *addr = hpdev->hbus->cfg_addr + CFG_PAGE_OFFSET + where;
+
+	/*
+	 * If the attempt is to read the IDs or the ROM BAR, simulate that.
+	 */
+	if (where + size <= PCI_COMMAND) {
+		memcpy(val, ((u8 *)&hpdev->desc.v_id) + where, size);
+	} else if (where >= PCI_CLASS_REVISION && where + size <=
+		   PCI_CACHE_LINE_SIZE) {
+		memcpy(val, ((u8 *)&hpdev->desc.rev) + where -
+		       PCI_CLASS_REVISION, size);
+	} else if (where >= PCI_SUBSYSTEM_VENDOR_ID && where + size <=
+		   PCI_ROM_ADDRESS) {
+		memcpy(val, (u8 *)&hpdev->desc.subsystem_id + where -
+		       PCI_SUBSYSTEM_VENDOR_ID, size);
+	} else if (where >= PCI_ROM_ADDRESS && where + size <=
+		   PCI_CAPABILITY_LIST) {
+		/* ROM BARs are unimplemented */
+		*val = 0;
+	} else if (where >= PCI_INTERRUPT_LINE && where + size <=
+		   PCI_INTERRUPT_PIN) {
+		/*
+		 * Interrupt Line and Interrupt PIN are hard-wired to zero
+		 * because this front-end only supports message-signaled
+		 * interrupts.
+		 */
+		*val = 0;
+	} else if (where + size <= CFG_PAGE_SIZE) {
+		spin_lock_irqsave(&hpdev->hbus->config_lock, flags);
+		/* Choose the function to be read. (See comment above) */
+		writel(hpdev->desc.win_slot.slot, hpdev->hbus->cfg_addr);
+		/* Read from that function's config space. */
+		switch (size) {
+		case 1:
+			*val = readb(addr);
+			break;
+		case 2:
+			*val = readw(addr);
+			break;
+		default:
+			*val = readl(addr);
+			break;
+		}
+		spin_unlock_irqrestore(&hpdev->hbus->config_lock, flags);
+	} else {
+		dev_err(&hpdev->hbus->hdev->device,
+			"Attempt to read beyond a function's config space.\n");
+	}
+}
+
+/**
+ * _hv_pcifront_write_config() - Internal PCI config write
+ * @hpdev:	The PCI driver's representation of the device
+ * @where:	Offset within config space
+ * @size:	Size of the transfer
+ * @val:	The data being transferred
+ */
+static void _hv_pcifront_write_config(struct hv_pci_dev *hpdev, int where,
+				      int size, u32 val)
+{
+	unsigned long flags;
+	void __iomem *addr = hpdev->hbus->cfg_addr + CFG_PAGE_OFFSET + where;
+
+	if (where >= PCI_SUBSYSTEM_VENDOR_ID &&
+	    where + size <= PCI_CAPABILITY_LIST) {
+		/* SSIDs and ROM BARs are read-only */
+	} else if (where >= PCI_COMMAND && where + size <= CFG_PAGE_SIZE) {
+		spin_lock_irqsave(&hpdev->hbus->config_lock, flags);
+		/* Choose the function to be written. (See comment above) */
+		writel(hpdev->desc.win_slot.slot, hpdev->hbus->cfg_addr);
+		/* Write to that function's config space. */
+		switch (size) {
+		case 1:
+			writeb(val, addr);
+			break;
+		case 2:
+			writew(val, addr);
+			break;
+		default:
+			writel(val, addr);
+			break;
+		}
+		spin_unlock_irqrestore(&hpdev->hbus->config_lock, flags);
+	} else {
+		dev_err(&hpdev->hbus->hdev->device,
+			"Attempt to write beyond a function's config space.\n");
+	}
+}
+
+/**
+ * hv_pcifront_read_config() - Read configuration space
+ * @bus: PCI Bus structure
+ * @devfn: Device/function
+ * @where: Offset from base
+ * @size: Byte/word/dword
+ * @val: Value to be read
+ *
+ * Return: PCIBIOS_SUCCESSFUL on success
+ *	   PCIBIOS_DEVICE_NOT_FOUND on failure
+ */
+static int hv_pcifront_read_config(struct pci_bus *bus, unsigned int devfn,
+				   int where, int size, u32 *val)
+{
+	struct hv_pcibus_device *hbus =
+		container_of(bus->sysdata, struct hv_pcibus_device, sysdata);
+	struct hv_pci_dev *hpdev;
+
+	hpdev = get_pcichild_wslot(hbus, devfn_to_wslot(devfn));
+	if (!hpdev)
+		return PCIBIOS_DEVICE_NOT_FOUND;
+
+	_hv_pcifront_read_config(hpdev, where, size, val);
+
+	put_pcichild(hpdev, hv_pcidev_ref_by_slot);
+	return PCIBIOS_SUCCESSFUL;
+}
+
+/**
+ * hv_pcifront_write_config() - Write configuration space
+ * @bus: PCI Bus structure
+ * @devfn: Device/function
+ * @where: Offset from base
+ * @size: Byte/word/dword
+ * @val: Value to be written to device
+ *
+ * Return: PCIBIOS_SUCCESSFUL on success
+ *	   PCIBIOS_DEVICE_NOT_FOUND on failure
+ */
+static int hv_pcifront_write_config(struct pci_bus *bus, unsigned int devfn,
+				    int where, int size, u32 val)
+{
+	struct hv_pcibus_device *hbus =
+	    container_of(bus->sysdata, struct hv_pcibus_device, sysdata);
+	struct hv_pci_dev *hpdev;
+
+	hpdev = get_pcichild_wslot(hbus, devfn_to_wslot(devfn));
+	if (!hpdev)
+		return PCIBIOS_DEVICE_NOT_FOUND;
+
+	_hv_pcifront_write_config(hpdev, where, size, val);
+
+	put_pcichild(hpdev, hv_pcidev_ref_by_slot);
+	return PCIBIOS_SUCCESSFUL;
+}
+
+/* PCIe operations */
+static struct pci_ops hv_pcifront_ops = {
+	.read  = hv_pcifront_read_config,
+	.write = hv_pcifront_write_config,
+};
+
+/* Interrupt management hooks */
+static void hv_int_desc_free(struct hv_pci_dev *hpdev,
+			     struct tran_int_desc *int_desc)
+{
+	struct pci_delete_interrupt *int_pkt;
+	struct {
+		struct pci_packet pkt;
+		u8 buffer[sizeof(struct pci_delete_interrupt) -
+			  sizeof(struct pci_message)];
+	} ctxt;
+
+	memset(&ctxt, 0, sizeof(ctxt));
+	int_pkt = (struct pci_delete_interrupt *)&ctxt.pkt.message;
+	int_pkt->message_type.message_type =
+		PCI_DELETE_INTERRUPT_MESSAGE;
+	int_pkt->wslot.slot = hpdev->desc.win_slot.slot;
+	int_pkt->int_desc = *int_desc;
+	vmbus_sendpacket(hpdev->hbus->hdev->channel, int_pkt,
+			 sizeof(*int_pkt),
+			 (unsigned long)&ctxt.pkt, VM_PKT_DATA_INBAND,
+			 0);
+	kfree(int_desc);
+}
+
+/**
+ * hv_msi_free() - Free the MSI.
+ * @domain:	The interrupt domain pointer
+ * @info:	Extra MSI-related context
+ * @irq:	Identifies the IRQ.
+ *
+ * The Hyper-V parent partition and hypervisor are tracking the
+ * messages that are in use, keeping the interrupt redirection
+ * table up to date.  This callback sends a message that frees
+ * the IRT entry and related tracking nonsense.
+ */
+static void hv_msi_free(struct irq_domain *domain, struct msi_domain_info *info,
+			unsigned int irq)
+{
+	struct hv_pcibus_device *hbus;
+	struct hv_pci_dev *hpdev;
+	struct pci_dev *pdev;
+	struct tran_int_desc *int_desc;
+	struct irq_data *irq_data = irq_domain_get_irq_data(domain, irq);
+	struct msi_desc *msi = irq_data_get_msi_desc(irq_data);
+
+	pdev = msi_desc_to_pci_dev(msi);
+	hbus = info->data;
+	hpdev = get_pcichild_wslot(hbus, devfn_to_wslot(pdev->devfn));
+	if (!hpdev)
+		return;
+
+	int_desc = irq_data_get_irq_chip_data(irq_data);
+	if (int_desc) {
+		irq_data->chip_data = NULL;
+		hv_int_desc_free(hpdev, int_desc);
+	}
+
+	put_pcichild(hpdev, hv_pcidev_ref_by_slot);
+}
+
+static int hv_set_affinity(struct irq_data *data, const struct cpumask *dest,
+			   bool force)
+{
+	struct irq_data *parent = data->parent_data;
+
+	return parent->chip->irq_set_affinity(parent, dest, force);
+}
+
+void hv_irq_mask(struct irq_data *data)
+{
+	pci_msi_mask_irq(data);
+}
+
+/**
+ * hv_irq_unmask() - "Unmask" the IRQ by setting its current
+ * affinity.
+ * @data:	Describes the IRQ
+ *
+ * Build new a destination for the MSI and make a hypercall to
+ * update the Interrupt Redirection Table. "Device Logical ID"
+ * is built out of this PCI bus's instance GUID and the function
+ * number of the device.
+ */
+void hv_irq_unmask(struct irq_data *data)
+{
+	struct msi_desc *msi_desc = irq_data_get_msi_desc(data);
+	struct irq_cfg *cfg = irqd_cfg(data);
+	struct retarget_msi_interrupt params;
+	struct hv_pcibus_device *hbus;
+	struct cpumask *dest;
+	struct pci_bus *pbus;
+	struct pci_dev *pdev;
+	int cpu;
+
+	dest = irq_data_get_affinity_mask(data);
+	pdev = msi_desc_to_pci_dev(msi_desc);
+	pbus = pdev->bus;
+	hbus = container_of(pbus->sysdata, struct hv_pcibus_device, sysdata);
+
+	memset(&params, 0, sizeof(params));
+	params.partition_id = HV_PARTITION_ID_SELF;
+	params.source = 1; /* MSI(-X) */
+	params.address = msi_desc->msg.address_lo;
+	params.data = msi_desc->msg.data;
+	params.device_id = (hbus->hdev->dev_instance.b[5] << 24) |
+			   (hbus->hdev->dev_instance.b[4] << 16) |
+			   (hbus->hdev->dev_instance.b[7] << 8) |
+			   (hbus->hdev->dev_instance.b[6] & 0xf8) |
+			   PCI_FUNC(pdev->devfn);
+	params.vector = cfg->vector;
+
+	for_each_cpu_and(cpu, dest, cpu_online_mask)
+		params.vp_mask |= (1ULL << vmbus_cpu_number_to_vp_number(cpu));
+
+	hv_do_hypercall(HVCALL_RETARGET_INTERRUPT, &params, NULL);
+
+	pci_msi_unmask_irq(data);
+}
+
+struct compose_comp_ctxt {
+	struct hv_pci_compl comp_pkt;
+	struct tran_int_desc int_desc;
+};
+
+static void hv_pci_compose_compl(void *context, struct pci_response *resp,
+				 int resp_packet_size)
+{
+	struct compose_comp_ctxt *comp_pkt = context;
+	struct pci_create_int_response *int_resp =
+		(struct pci_create_int_response *)resp;
+
+	comp_pkt->comp_pkt.completion_status = resp->status;
+	comp_pkt->int_desc = int_resp->int_desc;
+	complete(&comp_pkt->comp_pkt.host_event);
+}
+
+/**
+ * hv_compose_msi_msg() - Supplies a valid MSI address/data
+ * @data:	Everything about this MSI
+ * @msg:	Buffer that is filled in by this function
+ *
+ * This function unpacks the IRQ looking for target CPU set, IDT
+ * vector and mode and sends a message to the parent partition
+ * asking for a mapping for that tuple in this partition.  The
+ * response supplies a data value and address to which that data
+ * should be written to trigger that interrupt.
+ */
+static void hv_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
+{
+	struct irq_cfg *cfg = irqd_cfg(data);
+	struct hv_pcibus_device *hbus;
+	struct hv_pci_dev *hpdev;
+	struct pci_bus *pbus;
+	struct pci_dev *pdev;
+	struct pci_create_interrupt *int_pkt;
+	struct compose_comp_ctxt comp;
+	struct tran_int_desc *int_desc;
+	struct cpumask *affinity;
+	struct {
+		struct pci_packet pkt;
+		u8 buffer[sizeof(struct pci_create_interrupt) -
+			  sizeof(struct pci_message)];
+	} ctxt;
+	int cpu;
+	int ret;
+
+	pdev = msi_desc_to_pci_dev(irq_data_get_msi_desc(data));
+	pbus = pdev->bus;
+	hbus = container_of(pbus->sysdata, struct hv_pcibus_device, sysdata);
+	hpdev = get_pcichild_wslot(hbus, devfn_to_wslot(pdev->devfn));
+
+	if (!hpdev)
+		goto return_null_message;
+
+	/* Free any previous message that might have already been composed. */
+	if (data->chip_data) {
+		int_desc = data->chip_data;
+		data->chip_data = NULL;
+		hv_int_desc_free(hpdev, int_desc);
+	}
+
+	int_desc = kzalloc(sizeof(*int_desc), GFP_KERNEL);
+	if (!int_desc)
+		goto drop_reference;
+
+	memset(&ctxt, 0, sizeof(ctxt));
+	init_completion(&comp.comp_pkt.host_event);
+	ctxt.pkt.completion_func = hv_pci_compose_compl;
+	ctxt.pkt.compl_ctxt = &comp;
+	int_pkt = (struct pci_create_interrupt *)&ctxt.pkt.message;
+	int_pkt->message_type.message_type = PCI_CREATE_INTERRUPT_MESSAGE;
+	int_pkt->wslot.slot = hpdev->desc.win_slot.slot;
+	int_pkt->int_desc.vector = cfg->vector;
+	int_pkt->int_desc.vector_count = 1;
+	int_pkt->int_desc.delivery_mode =
+		(apic->irq_delivery_mode == dest_LowestPrio) ? 1 : 0;
+
+	/*
+	 * This bit doesn't have to work on machines with more than 64
+	 * processors because Hyper-V only supports 64 in a guest.
+	 */
+	affinity = irq_data_get_affinity_mask(data);
+	for_each_cpu_and(cpu, affinity, cpu_online_mask) {
+		int_pkt->int_desc.cpu_mask |=
+			(1ULL << vmbus_cpu_number_to_vp_number(cpu));
+	}
+
+	ret = vmbus_sendpacket(hpdev->hbus->hdev->channel, int_pkt,
+			       sizeof(*int_pkt), (unsigned long)&ctxt.pkt,
+			       VM_PKT_DATA_INBAND,
+			       VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
+	if (!ret)
+		wait_for_completion(&comp.comp_pkt.host_event);
+
+	if (comp.comp_pkt.completion_status < 0) {
+		dev_err(&hbus->hdev->device,
+			"Request for interrupt failed: 0x%x",
+			comp.comp_pkt.completion_status);
+		goto free_int_desc;
+	}
+
+	/*
+	 * Record the assignment so that this can be unwound later. Using
+	 * irq_set_chip_data() here would be appropriate, but the lock it takes
+	 * is already held.
+	 */
+	*int_desc = comp.int_desc;
+	data->chip_data = int_desc;
+
+	/* Pass up the result. */
+	msg->address_hi = comp.int_desc.address >> 32;
+	msg->address_lo = comp.int_desc.address & 0xffffffff;
+	msg->data = comp.int_desc.data;
+
+	put_pcichild(hpdev, hv_pcidev_ref_by_slot);
+	return;
+
+free_int_desc:
+	kfree(int_desc);
+drop_reference:
+	put_pcichild(hpdev, hv_pcidev_ref_by_slot);
+return_null_message:
+	msg->address_hi = 0;
+	msg->address_lo = 0;
+	msg->data = 0;
+}
+
+/* HW Interrupt Chip Descriptor */
+static struct irq_chip hv_msi_irq_chip = {
+	.name			= "Hyper-V PCIe MSI",
+	.irq_compose_msi_msg	= hv_compose_msi_msg,
+	.irq_set_affinity	= hv_set_affinity,
+	.irq_ack		= irq_chip_ack_parent,
+	.irq_mask		= hv_irq_mask,
+	.irq_unmask		= hv_irq_unmask,
+};
+
+static irq_hw_number_t hv_msi_domain_ops_get_hwirq(struct msi_domain_info *info,
+						   msi_alloc_info_t *arg)
+{
+	return arg->msi_hwirq;
+}
+
+static struct msi_domain_ops hv_msi_ops = {
+	.get_hwirq	= hv_msi_domain_ops_get_hwirq,
+	.msi_prepare	= pci_msi_prepare,
+	.set_desc	= pci_msi_set_desc,
+	.msi_free	= hv_msi_free,
+};
+
+/**
+ * hv_pcie_init_irq_domain() - Initialize IRQ domain
+ * @hbus:	The root PCI bus
+ *
+ * This function creates an IRQ domain which will be used for
+ * interrupts from devices that have been passed through.  These
+ * devices only support MSI and MSI-X, not line-based interrupts
+ * or simulations of line-based interrupts through PCIe's
+ * fabric-layer messages.  Because interrupts are remapped, we
+ * can support multi-message MSI here.
+ *
+ * Return: '0' on success and error value on failure
+ */
+static int hv_pcie_init_irq_domain(struct hv_pcibus_device *hbus)
+{
+	hbus->msi_info.chip = &hv_msi_irq_chip;
+	hbus->msi_info.ops = &hv_msi_ops;
+	hbus->msi_info.flags = (MSI_FLAG_USE_DEF_DOM_OPS |
+		MSI_FLAG_USE_DEF_CHIP_OPS | MSI_FLAG_MULTI_PCI_MSI |
+		MSI_FLAG_PCI_MSIX);
+	hbus->msi_info.handler = handle_edge_irq;
+	hbus->msi_info.handler_name = "edge";
+	hbus->msi_info.data = hbus;
+	hbus->irq_domain = pci_msi_create_irq_domain(hbus->sysdata.fwnode,
+						     &hbus->msi_info,
+						     x86_vector_domain);
+	if (!hbus->irq_domain) {
+		dev_err(&hbus->hdev->device,
+			"Failed to build an MSI IRQ domain\n");
+		return -ENODEV;
+	}
+
+	return 0;
+}
+
+/**
+ * get_bar_size() - Get the address space consumed by a BAR
+ * @bar_val:	Value that a BAR returned after -1 was written
+ *              to it.
+ *
+ * This function returns the size of the BAR, rounded up to 1
+ * page.  It has to be rounded up because the hypervisor's page
+ * table entry that maps the BAR into the VM can't specify an
+ * offset within a page.  The invariant is that the hypervisor
+ * must place any BARs of smaller than page length at the
+ * beginning of a page.
+ *
+ * Return:	Size in bytes of the consumed MMIO space.
+ */
+static u64 get_bar_size(u64 bar_val)
+{
+	return round_up((1 + ~(bar_val & PCI_BASE_ADDRESS_MEM_MASK)),
+			PAGE_SIZE);
+}
+
+/**
+ * survey_child_resources() - Total all MMIO requirements
+ * @hbus:	Root PCI bus, as understood by this driver
+ */
+static void survey_child_resources(struct hv_pcibus_device *hbus)
+{
+	struct list_head *iter;
+	struct hv_pci_dev *hpdev;
+	resource_size_t bar_size = 0;
+	unsigned long flags;
+	struct completion *event;
+	u64 bar_val;
+	int i;
+
+	/* If nobody is waiting on the answer, don't compute it. */
+	event = xchg(&hbus->survey_event, NULL);
+	if (!event)
+		return;
+
+	/* If the answer has already been computed, go with it. */
+	if (hbus->low_mmio_space || hbus->high_mmio_space) {
+		complete(event);
+		return;
+	}
+
+	spin_lock_irqsave(&hbus->device_list_lock, flags);
+
+	/*
+	 * Due to an interesting quirk of the PCI spec, all memory regions
+	 * for a child device are a power of 2 in size and aligned in memory,
+	 * so it's sufficient to just add them up without tracking alignment.
+	 */
+	list_for_each(iter, &hbus->children) {
+		hpdev = container_of(iter, struct hv_pci_dev, list_entry);
+		for (i = 0; i < 6; i++) {
+			if (hpdev->probed_bar[i] & PCI_BASE_ADDRESS_SPACE_IO)
+				dev_err(&hbus->hdev->device,
+					"There's an I/O BAR in this list!\n");
+
+			if (hpdev->probed_bar[i] != 0) {
+				/*
+				 * A probed BAR has all the upper bits set that
+				 * can be changed.
+				 */
+
+				bar_val = hpdev->probed_bar[i];
+				if (bar_val & PCI_BASE_ADDRESS_MEM_TYPE_64)
+					bar_val |=
+					((u64)hpdev->probed_bar[++i] << 32);
+				else
+					bar_val |= 0xffffffff00000000ULL;
+
+				bar_size = get_bar_size(bar_val);
+
+				if (bar_val & PCI_BASE_ADDRESS_MEM_TYPE_64)
+					hbus->high_mmio_space += bar_size;
+				else
+					hbus->low_mmio_space += bar_size;
+			}
+		}
+	}
+
+	spin_unlock_irqrestore(&hbus->device_list_lock, flags);
+	complete(event);
+}
+
+/**
+ * prepopulate_bars() - Fill in BARs with defaults
+ * @hbus:	Root PCI bus, as understood by this driver
+ *
+ * The core PCI driver code seems much, much happier if the BARs
+ * for a device have values upon first scan. So fill them in.
+ * The algorithm below works down from large sizes to small,
+ * attempting to pack the assignments optimally. The assumption,
+ * enforced in other parts of the code, is that the beginning of
+ * the memory-mapped I/O space will be aligned on the largest
+ * BAR size.
+ */
+static void prepopulate_bars(struct hv_pcibus_device *hbus)
+{
+	resource_size_t high_size = 0;
+	resource_size_t low_size = 0;
+	resource_size_t high_base = 0;
+	resource_size_t low_base = 0;
+	resource_size_t bar_size;
+	struct hv_pci_dev *hpdev;
+	struct list_head *iter;
+	unsigned long flags;
+	u64 bar_val;
+	u32 command;
+	bool high;
+	int i;
+
+	if (hbus->low_mmio_space) {
+		low_size = 1ULL << (63 - __builtin_clzll(hbus->low_mmio_space));
+		low_base = hbus->low_mmio_res->start;
+	}
+
+	if (hbus->high_mmio_space) {
+		high_size = 1ULL <<
+			(63 - __builtin_clzll(hbus->high_mmio_space));
+		high_base = hbus->high_mmio_res->start;
+	}
+
+	spin_lock_irqsave(&hbus->device_list_lock, flags);
+
+	/* Pick addresses for the BARs. */
+	do {
+		list_for_each(iter, &hbus->children) {
+			hpdev = container_of(iter, struct hv_pci_dev,
+					     list_entry);
+			for (i = 0; i < 6; i++) {
+				bar_val = hpdev->probed_bar[i];
+				if (bar_val == 0)
+					continue;
+				high = bar_val & PCI_BASE_ADDRESS_MEM_TYPE_64;
+				if (high) {
+					bar_val |=
+						((u64)hpdev->probed_bar[i + 1]
+						 << 32);
+				} else {
+					bar_val |= 0xffffffffULL << 32;
+				}
+				bar_size = get_bar_size(bar_val);
+				if (high) {
+					if (high_size != bar_size) {
+						i++;
+						continue;
+					}
+					_hv_pcifront_write_config(hpdev,
+						PCI_BASE_ADDRESS_0 + (4 * i),
+						4,
+						(u32)(high_base & 0xffffff00));
+					i++;
+					_hv_pcifront_write_config(hpdev,
+						PCI_BASE_ADDRESS_0 + (4 * i),
+						4, (u32)(high_base >> 32));
+					high_base += bar_size;
+				} else {
+					if (low_size != bar_size)
+						continue;
+					_hv_pcifront_write_config(hpdev,
+						PCI_BASE_ADDRESS_0 + (4 * i),
+						4,
+						(u32)(low_base & 0xffffff00));
+					low_base += bar_size;
+				}
+			}
+			if (high_size <= 1 && low_size <= 1) {
+				/* Set the memory enable bit. */
+				_hv_pcifront_read_config(hpdev, PCI_COMMAND, 2,
+							 &command);
+				command |= PCI_COMMAND_MEMORY;
+				_hv_pcifront_write_config(hpdev, PCI_COMMAND, 2,
+							  command);
+				break;
+			}
+		}
+
+		high_size >>= 1;
+		low_size >>= 1;
+	}  while (high_size || low_size);
+
+	spin_unlock_irqrestore(&hbus->device_list_lock, flags);
+}
+
+/**
+ * create_root_hv_pci_bus() - Expose a new root PCI bus
+ * @hbus:	Root PCI bus, as understood by this driver
+ *
+ * Return: 0 on success, -errno on failure
+ */
+static int create_root_hv_pci_bus(struct hv_pcibus_device *hbus)
+{
+	/* Register the device */
+	hbus->pci_bus = pci_create_root_bus(&hbus->hdev->device,
+					    0, /* bus number is always zero */
+					    &hv_pcifront_ops,
+					    &hbus->sysdata,
+					    &hbus->resources_for_children);
+	if (!hbus->pci_bus)
+		return -ENODEV;
+
+	hbus->pci_bus->msi = &hbus->msi_chip;
+	hbus->pci_bus->msi->dev = &hbus->hdev->device;
+
+	pci_scan_child_bus(hbus->pci_bus);
+	pci_bus_assign_resources(hbus->pci_bus);
+	pci_bus_add_devices(hbus->pci_bus);
+	hbus->state = hv_pcibus_installed;
+	return 0;
+}
+
+struct q_res_req_compl {
+	struct completion host_event;
+	struct hv_pci_dev *hpdev;
+};
+
+/**
+ * q_resource_requirements() - Query Resource Requirements
+ * @context:		The completion context.
+ * @resp:		The response that came from the host.
+ * @resp_packet_size:	The size in bytes of resp.
+ *
+ * This function is invoked on completion of a Query Resource
+ * Requirements packet.
+ */
+static void q_resource_requirements(void *context, struct pci_response *resp,
+				    int resp_packet_size)
+{
+	struct q_res_req_compl *completion = context;
+	struct pci_q_res_req_response *q_res_req =
+		(struct pci_q_res_req_response *)resp;
+	int i;
+
+	if (resp->status < 0) {
+		dev_err(&completion->hpdev->hbus->hdev->device,
+			"query resource requirements failed: %x\n",
+			resp->status);
+	} else {
+		for (i = 0; i < 6; i++) {
+			completion->hpdev->probed_bar[i] =
+				q_res_req->probed_bar[i];
+		}
+	}
+
+	complete(&completion->host_event);
+}
+
+static void get_pcichild(struct hv_pci_dev *hpdev,
+			    enum hv_pcidev_ref_reason reason)
+{
+	atomic_inc(&hpdev->refs);
+}
+
+static void put_pcichild(struct hv_pci_dev *hpdev,
+			    enum hv_pcidev_ref_reason reason)
+{
+	if (atomic_dec_and_test(&hpdev->refs))
+		kfree(hpdev);
+}
+
+/**
+ * new_pcichild_device() - Create a new child device
+ * @hbus:	The internal struct tracking this root PCI bus.
+ * @desc:	The information supplied so far from the host
+ *              about the device.
+ *
+ * This function creates the tracking structure for a new child
+ * device and kicks off the process of figuring out what it is.
+ *
+ * Return: Pointer to the new tracking struct
+ */
+static struct hv_pci_dev *new_pcichild_device(struct hv_pcibus_device *hbus,
+		struct pci_function_description *desc)
+{
+	struct hv_pci_dev *hpdev;
+	struct pci_child_message *res_req;
+	struct q_res_req_compl comp_pkt;
+	union {
+	struct pci_packet init_packet;
+		u8 buffer[0x100];
+	} pkt;
+	unsigned long flags;
+	int ret;
+
+	hpdev = kzalloc(sizeof(*hpdev), GFP_ATOMIC);
+	if (!hpdev)
+		return NULL;
+
+	dev_info(&hbus->hdev->device,
+		 "New child device (%p) [%04x:%04x] at %04x:00:00.%02x\n",
+		 hpdev, desc->v_id, desc->d_id, pci_domain_nr(hbus->pci_bus),
+		 desc->win_slot.bits.func);
+
+	hpdev->hbus = hbus;
+
+	memset(&pkt, 0, sizeof(pkt));
+	init_completion(&comp_pkt.host_event);
+	comp_pkt.hpdev = hpdev;
+	pkt.init_packet.compl_ctxt = &comp_pkt;
+	pkt.init_packet.completion_func = q_resource_requirements;
+	res_req = (struct pci_child_message *)&pkt.init_packet.message;
+	res_req->message_type = PCI_QUERY_RESOURCE_REQUIREMENTS;
+	res_req->wslot.slot = desc->win_slot.slot;
+
+	ret = vmbus_sendpacket(hbus->hdev->channel, res_req,
+			       sizeof(struct pci_child_message),
+			       (unsigned long)&pkt.init_packet,
+			       VM_PKT_DATA_INBAND,
+			       VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
+	if (ret)
+		goto error;
+
+	wait_for_completion(&comp_pkt.host_event);
+
+	hpdev->desc = *desc;
+	get_pcichild(hpdev, hv_pcidev_ref_initial);
+	get_pcichild(hpdev, hv_pcidev_ref_childlist);
+	spin_lock_irqsave(&hbus->device_list_lock, flags);
+	list_add_tail(&hpdev->list_entry, &hbus->children);
+	spin_unlock_irqrestore(&hbus->device_list_lock, flags);
+	return hpdev;
+
+error:
+
+	kfree(hpdev);
+	return NULL;
+}
+
+/**
+ * get_pcichild_wslot() - Find device from slot
+ * @hbus:	Root PCI bus, as understood by this driver
+ * @wslot:	Location on the bus
+ *
+ * This function looks up a PCI device and returns the internal
+ * representation of it.  It acquires a reference on it, so that
+ * the device won't be deleted while somebody is using it.  The
+ * caller is responsible for calling put_pcichild() to release
+ * this reference.
+ *
+ * Return:	Internal representation of a PCI device
+ */
+static struct hv_pci_dev *get_pcichild_wslot(struct hv_pcibus_device *hbus,
+					     u32 wslot)
+{
+	unsigned long flags;
+	struct hv_pci_dev *iter, *hpdev = NULL;
+
+	spin_lock_irqsave(&hbus->device_list_lock, flags);
+	list_for_each_entry(iter, &hbus->children, list_entry) {
+		if (iter->desc.win_slot.slot == wslot) {
+			hpdev = iter;
+			get_pcichild(hpdev, hv_pcidev_ref_by_slot);
+			break;
+		}
+	}
+	spin_unlock_irqrestore(&hbus->device_list_lock, flags);
+
+	return hpdev;
+}
+
+/**
+ * pci_devices_present_work() - Handle new list of child devices
+ * @work:	Work struct embedded in struct hv_dr_work
+ *
+ * "Bus Relations" is the Windows term for "children of this
+ * bus."  The terminology is preserved here for people trying to
+ * debug the interaction between Hyper-V and Linux.  This
+ * function is called when the parent partition reports a list
+ * of functions that should be observed under this PCI Express
+ * port (bus).
+ *
+ * This function updates the list, and must tolerate being
+ * called multiple times with the same information.  The typical
+ * number of child devices is one, with very atypical cases
+ * involving three or four, so the algorithms used here can be
+ * simple and inefficient.
+ *
+ * It must also treat the omission of a previously observed device as
+ * notification that the device no longer exists.
+ *
+ * Note that this function is a work item, and it may not be
+ * invoked in the order that it was queued.  Back to back
+ * updates of the list of present devices may involve queuing
+ * multiple work items, and this one may run before ones that
+ * were sent later. As such, this function only does something
+ * if is the last one in the queue.
+ */
+static void pci_devices_present_work(struct work_struct *work)
+{
+	u32 child_no;
+	bool found;
+	struct list_head *iter;
+	struct pci_function_description *new_desc;
+	struct hv_pci_dev *hpdev;
+	struct hv_pcibus_device *hbus;
+	struct list_head removed;
+	struct hv_dr_work *dr_wrk;
+	struct hv_dr_state *dr = NULL;
+	unsigned long flags;
+
+	dr_wrk = container_of(work, struct hv_dr_work, wrk);
+	hbus = dr_wrk->bus;
+	kfree(dr_wrk);
+
+	INIT_LIST_HEAD(&removed);
+
+	if (down_interruptible(&hbus->enum_sem)) {
+		put_hvpcibus(hbus);
+		return;
+	}
+
+	/* Pull this off the queue and process it if it was the last one. */
+	spin_lock_irqsave(&hbus->device_list_lock, flags);
+	while (!list_empty(&hbus->dr_list)) {
+		dr = list_first_entry(&hbus->dr_list, struct hv_dr_state,
+				      list_entry);
+		list_del(&dr->list_entry);
+
+		/* Throw this away if the list still has stuff in it. */
+		if (!list_empty(&hbus->dr_list)) {
+			kfree(dr);
+			continue;
+		}
+	}
+	spin_unlock_irqrestore(&hbus->device_list_lock, flags);
+
+	if (!dr) {
+		up(&hbus->enum_sem);
+		put_hvpcibus(hbus);
+		return;
+	}
+
+	/* First, mark all existing children as reported missing. */
+	spin_lock_irqsave(&hbus->device_list_lock, flags);
+	list_for_each(iter, &hbus->children) {
+			hpdev = container_of(iter, struct hv_pci_dev,
+					     list_entry);
+			hpdev->reported_missing = true;
+	}
+	spin_unlock_irqrestore(&hbus->device_list_lock, flags);
+
+	/* Next, add back any reported devices. */
+	for (child_no = 0; child_no < dr->device_count; child_no++) {
+		found = false;
+		new_desc = &dr->func[child_no];
+
+		spin_lock_irqsave(&hbus->device_list_lock, flags);
+		list_for_each(iter, &hbus->children) {
+			hpdev = container_of(iter, struct hv_pci_dev,
+					     list_entry);
+			if ((hpdev->desc.win_slot.slot ==
+			     new_desc->win_slot.slot) &&
+			    (hpdev->desc.v_id == new_desc->v_id) &&
+			    (hpdev->desc.d_id == new_desc->d_id) &&
+			    (hpdev->desc.ser == new_desc->ser)) {
+				hpdev->reported_missing = false;
+				found = true;
+			}
+		}
+		spin_unlock_irqrestore(&hbus->device_list_lock, flags);
+
+		if (!found) {
+			hpdev = new_pcichild_device(hbus, new_desc);
+			if (!hpdev)
+				dev_err(&hbus->hdev->device,
+					"couldn't record a child device.\n");
+		}
+	}
+
+	/* Move missing children to a list on the stack. */
+	spin_lock_irqsave(&hbus->device_list_lock, flags);
+	do {
+		found = false;
+		list_for_each(iter, &hbus->children) {
+			hpdev = container_of(iter, struct hv_pci_dev,
+					     list_entry);
+			if (hpdev->reported_missing) {
+				found = true;
+				put_pcichild(hpdev, hv_pcidev_ref_childlist);
+				list_del(&hpdev->list_entry);
+				list_add_tail(&hpdev->list_entry, &removed);
+				break;
+			}
+		}
+	} while (found);
+	spin_unlock_irqrestore(&hbus->device_list_lock, flags);
+
+	/* Delete everything that should no longer exist. */
+	while (!list_empty(&removed)) {
+		hpdev = list_first_entry(&removed, struct hv_pci_dev,
+					 list_entry);
+		list_del(&hpdev->list_entry);
+		put_pcichild(hpdev, hv_pcidev_ref_initial);
+	}
+
+	/* Tell the core to rescan bus because there may have been changes. */
+	if (hbus->state == hv_pcibus_installed) {
+		pci_lock_rescan_remove();
+		pci_scan_child_bus(hbus->pci_bus);
+		pci_unlock_rescan_remove();
+	} else {
+		survey_child_resources(hbus);
+	}
+
+	up(&hbus->enum_sem);
+	put_hvpcibus(hbus);
+	kfree(dr);
+}
+
+/**
+ * hv_pci_devices_present() - Handles list of new children
+ * @hbus:	Root PCI bus, as understood by this driver
+ * @relations:	Packet from host listing children
+ *
+ * This function is invoked whenever a new list of devices for
+ * this bus appears.
+ */
+static void hv_pci_devices_present(struct hv_pcibus_device *hbus,
+				   struct pci_bus_relations *relations)
+{
+	struct hv_dr_state *dr;
+	struct hv_dr_work *dr_wrk;
+	unsigned long flags;
+
+	dr_wrk = kzalloc(sizeof(*dr_wrk), GFP_NOWAIT);
+
+	if (!dr_wrk)
+		return;
+
+	dr = kzalloc(offsetof(struct hv_dr_state, func) +
+		     (sizeof(struct pci_function_description) *
+		      (relations->device_count)), GFP_NOWAIT);
+
+	if (!dr)  {
+		kfree(dr_wrk);
+		return;
+	}
+
+	INIT_WORK(&dr_wrk->wrk, pci_devices_present_work);
+	dr_wrk->bus = hbus;
+	dr->device_count = relations->device_count;
+	if (dr->device_count != 0) {
+		memcpy(dr->func, relations->func,
+		       sizeof(struct pci_function_description) *
+		       dr->device_count);
+	}
+
+	spin_lock_irqsave(&hbus->device_list_lock, flags);
+	list_add_tail(&dr->list_entry, &hbus->dr_list);
+	spin_unlock_irqrestore(&hbus->device_list_lock, flags);
+
+	get_hvpcibus(hbus);
+	schedule_work(&dr_wrk->wrk);
+}
+
+/**
+ * hv_eject_device_work() - Asynchronously handles ejection
+ * @work:	Work struct embedded in internal device struct
+ *
+ * This function handles ejecting a device.  Windows will
+ * attempt to gracefully eject a device, waiting 60 seconds to
+ * hear back from the guest OS that this completed successfully.
+ * If this timer expires, the device will be forcibly removed.
+ */
+static void hv_eject_device_work(struct work_struct *work)
+{
+	struct pci_eject_response *ejct_pkt;
+	struct hv_pci_dev *hpdev;
+	struct pci_dev *pdev;
+	unsigned long flags;
+	int wslot;
+	struct {
+		struct pci_packet pkt;
+		u8 buffer[sizeof(struct pci_eject_response) -
+			  sizeof(struct pci_message)];
+	} ctxt;
+
+	hpdev = container_of(work, struct hv_pci_dev, wrk);
+
+	if (hpdev->state != hv_pcichild_ejecting) {
+		put_pcichild(hpdev, hv_pcidev_ref_pnp);
+		return;
+	}
+
+	wslot = wslot_to_devfn(hpdev->desc.win_slot.slot);
+	pdev = pci_get_domain_bus_and_slot(pci_domain_nr(hpdev->hbus->pci_bus),
+					   0, wslot);
+	if (pdev) {
+		pci_stop_and_remove_bus_device(pdev);
+		pci_dev_put(pdev);
+	}
+
+	memset(&ctxt, 0, sizeof(ctxt));
+	ejct_pkt = (struct pci_eject_response *)&ctxt.pkt.message;
+	ejct_pkt->message_type = PCI_EJECTION_COMPLETE;
+	ejct_pkt->wslot.slot = hpdev->desc.win_slot.slot;
+	vmbus_sendpacket(hpdev->hbus->hdev->channel, ejct_pkt,
+			 sizeof(*ejct_pkt), (unsigned long)&ctxt.pkt,
+			 VM_PKT_DATA_INBAND, 0);
+
+	spin_lock_irqsave(&hpdev->hbus->device_list_lock, flags);
+	list_del(&hpdev->list_entry);
+	spin_unlock_irqrestore(&hpdev->hbus->device_list_lock, flags);
+
+	put_pcichild(hpdev, hv_pcidev_ref_childlist);
+	put_pcichild(hpdev, hv_pcidev_ref_pnp);
+	put_hvpcibus(hpdev->hbus);
+}
+
+/**
+ * hv_pci_eject_device() - Handles device ejection
+ * @hpdev:	Internal device tracking struct
+ *
+ * This function is invoked when an ejection packet arrives.  It
+ * just schedules work so that we don't re-enter the packet
+ * delivery code handling the ejection.
+ */
+static void hv_pci_eject_device(struct hv_pci_dev *hpdev)
+{
+	hpdev->state = hv_pcichild_ejecting;
+	get_pcichild(hpdev, hv_pcidev_ref_pnp);
+	INIT_WORK(&hpdev->wrk, hv_eject_device_work);
+	get_hvpcibus(hpdev->hbus);
+	schedule_work(&hpdev->wrk);
+}
+
+/**
+ * hv_pci_onchannelcallback() - Handles incoming packets
+ * @context:	Internal bus tracking struct
+ *
+ * This function is invoked whenever the host sends a packet to
+ * this channel (which is private to this root PCI bus).
+ */
+static void hv_pci_onchannelcallback(void *context)
+{
+	const int packet_size = 0x100;
+	int ret;
+	struct hv_pcibus_device *hbus = context;
+	u32 bytes_recvd;
+	u64 req_id;
+	struct vmpacket_descriptor *desc;
+	unsigned char *buffer;
+	int bufferlen = packet_size;
+	struct pci_packet *comp_packet;
+	struct pci_response *response;
+	struct pci_incoming_message *new_message;
+	struct pci_bus_relations *bus_rel;
+	struct pci_dev_incoming *dev_message;
+	struct hv_pci_dev *hpdev;
+
+	buffer = kmalloc(bufferlen, GFP_ATOMIC);
+	if (!buffer)
+		return;
+
+	while (1) {
+		ret = vmbus_recvpacket_raw(hbus->hdev->channel, buffer,
+					   bufferlen, &bytes_recvd, &req_id);
+
+		if (ret == -ENOBUFS) {
+			kfree(buffer);
+			/* Handle large packet */
+			bufferlen = bytes_recvd;
+			buffer = kmalloc(bytes_recvd, GFP_ATOMIC);
+			if (!buffer)
+				return;
+			continue;
+		}
+
+		/*
+		 * All incoming packets must be at least as large as a
+		 * response.
+		 */
+		if (bytes_recvd <= sizeof(struct pci_response)) {
+			kfree(buffer);
+			return;
+		}
+		desc = (struct vmpacket_descriptor *)buffer;
+
+		switch (desc->type) {
+		case VM_PKT_COMP:
+
+			/*
+			 * The host is trusted, and thus it's safe to interpret
+			 * this transaction ID as a pointer.
+			 */
+			comp_packet = (struct pci_packet *)req_id;
+			response = (struct pci_response *)buffer;
+			comp_packet->completion_func(comp_packet->compl_ctxt,
+						     response,
+						     bytes_recvd);
+			kfree(buffer);
+			return;
+
+		case VM_PKT_DATA_INBAND:
+
+			new_message = (struct pci_incoming_message *)buffer;
+			switch (new_message->message_type.message_type) {
+			case PCI_BUS_RELATIONS:
+
+				bus_rel = (struct pci_bus_relations *)buffer;
+				if (bytes_recvd <
+				    offsetof(struct pci_bus_relations, func) +
+				    (sizeof(struct pci_function_description) *
+				     (bus_rel->device_count))) {
+					dev_err(&hbus->hdev->device,
+						"bus relations too small\n");
+					break;
+				}
+
+				hv_pci_devices_present(hbus, bus_rel);
+				break;
+
+			case PCI_EJECT:
+
+				dev_message = (struct pci_dev_incoming *)buffer;
+				hpdev = get_pcichild_wslot(hbus,
+						      dev_message->wslot.slot);
+				if (hpdev) {
+					hv_pci_eject_device(hpdev);
+					put_pcichild(hpdev,
+							hv_pcidev_ref_by_slot);
+				}
+				break;
+
+			default:
+				dev_warn(&hbus->hdev->device,
+					"Unimplemented protocol message %x\n",
+					new_message->message_type.message_type);
+				break;
+			}
+			break;
+
+		default:
+			dev_err(&hbus->hdev->device,
+				"unhandled packet type %d, tid %llx len %d\n",
+				desc->type, req_id, bytes_recvd);
+			break;
+		}
+		break;
+	}
+}
+
+/**
+ * hv_pci_protocol_negotiation() - Set up protocol
+ * @hdev:	VMBus's tracking struct for this root PCI bus
+ *
+ * This driver is intended to support running on Windows 10
+ * (server) and later versions. It will not run on earlier
+ * versions, as they assume that many of the operations which
+ * Linux needs accomplished with a spinlock held were done via
+ * asynchronous messaging via VMBus.  Windows 10 increases the
+ * surface area of PCI emulation so that these actions can take
+ * place by suspending a virtual processor for their duration.
+ *
+ * This function negotiates the channel protocol version,
+ * failing if the host doesn't support the necessary protocol
+ * level.
+ */
+static int hv_pci_protocol_negotiation(struct hv_device *hdev)
+{
+	struct pci_version_request *version_req;
+	struct hv_pci_compl comp_pkt;
+	struct pci_packet *pkt;
+	int ret;
+
+	/*
+	 * Initiate the handshake with the host and negotiate
+	 * a version that the host can support. We start with the
+	 * highest version number and go down if the host cannot
+	 * support it.
+	 */
+
+	pkt = kzalloc(sizeof(*pkt) + sizeof(*version_req), GFP_KERNEL);
+	if (!pkt)
+		return -ENOMEM;
+
+	init_completion(&comp_pkt.host_event);
+	pkt->completion_func = hv_pci_generic_compl;
+	pkt->compl_ctxt = &comp_pkt;
+	version_req = (struct pci_version_request *)&pkt->message;
+	version_req->message_type.message_type = PCI_QUERY_PROTOCOL_VERSION;
+	version_req->protocol_version = PCI_PROTOCOL_VERSION_CURRENT;
+
+	ret = vmbus_sendpacket(hdev->channel, version_req,
+			       sizeof(struct pci_version_request),
+			       (unsigned long)pkt, VM_PKT_DATA_INBAND,
+			       VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
+	if (ret)
+		goto exit;
+
+	wait_for_completion(&comp_pkt.host_event);
+
+	if (comp_pkt.completion_status < 0) {
+		dev_err(&hdev->device,
+			"PCI Pass-through VSP failed version request %x\n",
+			comp_pkt.completion_status);
+		ret = -EPROTO;
+		goto exit;
+	}
+
+	ret = 0;
+
+exit:
+
+	kfree(pkt);
+	return ret;
+}
+
+/**
+ * hv_pci_free_bridge_windows() - Release memory regions for the
+ * bus
+ * @hbus:	Root PCI bus, as understood by this driver
+ */
+static void hv_pci_free_bridge_windows(struct hv_pcibus_device *hbus)
+{
+	/*
+	 * Set the resources back to the way they looked when they
+	 * were allocated by setting IORESOURCE_BUSY again.
+	 */
+
+	if (hbus->low_mmio_space && hbus->low_mmio_res) {
+		hbus->low_mmio_res->flags |= IORESOURCE_BUSY;
+		release_mem_region(hbus->low_mmio_res->start,
+				   resource_size(hbus->low_mmio_res));
+	}
+
+	if (hbus->high_mmio_space && hbus->high_mmio_res) {
+		hbus->high_mmio_res->flags |= IORESOURCE_BUSY;
+		release_mem_region(hbus->high_mmio_res->start,
+				   resource_size(hbus->high_mmio_res));
+	}
+}
+
+/**
+ * hv_pci_allocate_bridge_windows() - Allocate memory regions
+ * for the bus
+ * @hbus:	Root PCI bus, as understood by this driver
+ *
+ * This function calls vmbus_allocate_mmio(), which is itself a
+ * bit of a compromise.  Ideally, we might change the pnp layer
+ * in the kernel such that it comprehends either PCI devices
+ * which are "grandchildren of ACPI," with some intermediate bus
+ * node (in this case, VMBus) or change it such that it
+ * understands VMBus.  The pnp layer, however, has been declared
+ * deprecated, and not subject to change.
+ *
+ * The workaround, implemented here, is to ask VMBus to allocate
+ * MMIO space for this bus.  VMBus itself knows which ranges are
+ * appropriate by looking at its own ACPI objects.  Then, after
+ * these ranges are claimed, they're modified to look like they
+ * would have looked if the ACPI and pnp code had allocated
+ * bridge windows.  These descriptors have to exist in this form
+ * in order to satisfy the code which will get invoked when the
+ * endpoint PCI function driver calls request_mem_region() or
+ * request_mem_region_exclusive().
+ *
+ * Return: 0 on success, -errno on failure
+ */
+static int hv_pci_allocate_bridge_windows(struct hv_pcibus_device *hbus)
+{
+	resource_size_t align;
+	int ret;
+
+	if (hbus->low_mmio_space) {
+		align = 1ULL << (63 - __builtin_clzll(hbus->low_mmio_space));
+		ret = vmbus_allocate_mmio(&hbus->low_mmio_res, hbus->hdev, 0,
+					  (u64)(u32)0xffffffff,
+					  hbus->low_mmio_space,
+					  align, false);
+		if (ret) {
+			dev_err(&hbus->hdev->device,
+				"Need %#llx of low MMIO space. Consider reconfiguring the VM.\n",
+				hbus->low_mmio_space);
+			return ret;
+		}
+
+		/* Modify this resource to become a bridge window. */
+		hbus->low_mmio_res->flags |= IORESOURCE_WINDOW;
+		hbus->low_mmio_res->flags &= ~IORESOURCE_BUSY;
+		pci_add_resource(&hbus->resources_for_children,
+				 hbus->low_mmio_res);
+	}
+
+	if (hbus->high_mmio_space) {
+		align = 1ULL << (63 - __builtin_clzll(hbus->high_mmio_space));
+		ret = vmbus_allocate_mmio(&hbus->high_mmio_res, hbus->hdev,
+					  0x100000000, -1,
+					  hbus->high_mmio_space, align,
+					  false);
+		if (ret) {
+			dev_err(&hbus->hdev->device,
+				"Need %#llx of high MMIO space. Consider reconfiguring the VM.\n",
+				hbus->high_mmio_space);
+			goto release_low_mmio;
+		}
+
+		/* Modify this resource to become a bridge window. */
+		hbus->high_mmio_res->flags |= IORESOURCE_WINDOW;
+		hbus->high_mmio_res->flags &= ~IORESOURCE_BUSY;
+		pci_add_resource(&hbus->resources_for_children,
+				 hbus->high_mmio_res);
+	}
+
+	return 0;
+
+release_low_mmio:
+
+	if (hbus->low_mmio_res) {
+		release_mem_region(hbus->low_mmio_res->start,
+				   resource_size(hbus->low_mmio_res));
+	}
+
+	return ret;
+}
+
+/**
+ * hv_allocate_config_window() - Find MMIO space for PCI Config
+ * @hbus:	Root PCI bus, as understood by this driver
+ *
+ * This function claims memory-mapped I/O space for accessing
+ * configuration space for the functions on this bus.
+ *
+ * Return: 0 on success, -errno on failure
+ */
+static int hv_allocate_config_window(struct hv_pcibus_device *hbus)
+{
+	int ret;
+
+	/*
+	 * Set up a region of MMIO space to use for accessing configuration
+	 * space.
+	 */
+	ret = vmbus_allocate_mmio(&hbus->mem_config, hbus->hdev, 0, -1,
+				  PCI_CONFIG_MMIO_LENGTH, 0x1000, false);
+	if (ret)
+		return ret;
+
+	/*
+	 * vmbus_allocate_mmio() gets used for allocating both device endpoint
+	 * resource claims (those which cannot be overlapped) and the ranges
+	 * which are valid for the children of this bus, which are intended
+	 * to be overlapped by those children.  Set the flag on this claim
+	 * meaning that this region can't be overlapped.
+	 */
+
+	hbus->mem_config->flags |= IORESOURCE_BUSY;
+
+	return 0;
+}
+
+static void hv_free_config_window(struct hv_pcibus_device *hbus)
+{
+	release_mem_region(hbus->mem_config->start, PCI_CONFIG_MMIO_LENGTH);
+}
+
+/**
+ * hv_pci_enter_d0() - Bring the "bus" into the D0 power state
+ * @hdev:	VMBus's tracking struct for this root PCI bus
+ *
+ * Return: 0 on success, -errno on failure
+ */
+static int hv_pci_enter_d0(struct hv_device *hdev)
+{
+	struct hv_pcibus_device *hbus = hv_get_drvdata(hdev);
+	struct pci_bus_d0_entry *d0_entry;
+	struct hv_pci_compl comp_pkt;
+	struct pci_packet *pkt;
+	int ret;
+
+	/*
+	 * Tell the host that the bus is ready to use, and moved into the
+	 * powered-on state.  This includes telling the host which region
+	 * of memory-mapped I/O space has been chosen for configuration space
+	 * access.
+	 */
+
+	pkt = kzalloc(sizeof(*pkt) + sizeof(*d0_entry), GFP_KERNEL);
+	if (!pkt)
+		return -ENOMEM;
+
+	init_completion(&comp_pkt.host_event);
+	pkt->completion_func = hv_pci_generic_compl;
+	pkt->compl_ctxt = &comp_pkt;
+	d0_entry = (struct pci_bus_d0_entry *)&pkt->message;
+	d0_entry->message_type.message_type = PCI_BUS_D0ENTRY;
+	d0_entry->mmio_base = hbus->mem_config->start;
+
+	ret = vmbus_sendpacket(hdev->channel, d0_entry, sizeof(*d0_entry),
+			       (unsigned long)pkt, VM_PKT_DATA_INBAND,
+			       VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
+	if (ret)
+		goto exit;
+	wait_for_completion(&comp_pkt.host_event);
+
+	if (comp_pkt.completion_status < 0) {
+		dev_err(&hdev->device,
+			"PCI Pass-through VSP failed D0 Entry with status %x\n",
+			comp_pkt.completion_status);
+		ret = -EPROTO;
+		goto exit;
+	}
+
+	ret = 0;
+
+exit:
+
+	kfree(pkt);
+	return ret;
+}
+
+/**
+ * hv_pci_query_relations() - Ask host to send list of child
+ * devices
+ * @hdev:	VMBus's tracking struct for this root PCI bus
+ *
+ * Return: 0 on success, -errno on failure
+ */
+static int hv_pci_query_relations(struct hv_device *hdev)
+{
+	struct hv_pcibus_device *hbus = hv_get_drvdata(hdev);
+	struct pci_message message;
+	struct completion comp;
+	int ret;
+
+	/*
+	 * Ask the host to send along the list of child devices.
+	 */
+
+	init_completion(&comp);
+	if (cmpxchg(&hbus->survey_event, NULL, &comp))
+		return -ENOTEMPTY;
+
+	memset(&message, 0, sizeof(message));
+	message.message_type = PCI_QUERY_BUS_RELATIONS;
+
+	ret = vmbus_sendpacket(hdev->channel, &message, sizeof(message),
+			       0, VM_PKT_DATA_INBAND, 0);
+	if (ret)
+		return ret;
+
+	wait_for_completion(&comp);
+	return 0;
+}
+
+/**
+ * hv_send_resources_allocated() - Report local resource choices
+ * @hdev:	VMBus's tracking struct for this root PCI bus
+ *
+ * The host OS is expecting to be sent a request as a message
+ * which contains all the resources that the device will use.
+ * The response contains those same resources, "translated"
+ * which is to say, the values which should be used by the
+ * hardware, when it delivers an interrupt.  (MMIO resources are
+ * used in local terms.)  This is nice for Windows, and lines up
+ * with the FDO/PDO split, which doesn't exist in Linux.  Linux
+ * is deeply expecting to scan an emulated PCI configuration
+ * space.  So this message is sent here only to drive the state
+ * machine on the host forward.
+ *
+ * Return: 0 on success, -errno on failure
+ */
+static int hv_send_resources_allocated(struct hv_device *hdev)
+{
+	struct hv_pcibus_device *hbus = hv_get_drvdata(hdev);
+	struct pci_resources_assigned *res_assigned;
+	struct hv_pci_compl comp_pkt;
+	struct hv_pci_dev *hpdev;
+	struct pci_packet *pkt;
+	u32 wslot;
+	int ret;
+
+	pkt = kmalloc(sizeof(*pkt) + sizeof(*res_assigned), GFP_KERNEL);
+	if (!pkt)
+		return -ENOMEM;
+
+	ret = 0;
+
+	for (wslot = 0; wslot < 256; wslot++) {
+		hpdev = get_pcichild_wslot(hbus, wslot);
+		if (!hpdev)
+			continue;
+
+		memset(pkt, 0, sizeof(*pkt) + sizeof(*res_assigned));
+		init_completion(&comp_pkt.host_event);
+		pkt->completion_func = hv_pci_generic_compl;
+		pkt->compl_ctxt = &comp_pkt;
+		pkt->message.message_type = PCI_RESOURCES_ASSIGNED;
+		res_assigned = (struct pci_resources_assigned *)&pkt->message;
+		res_assigned->wslot.slot = hpdev->desc.win_slot.slot;
+
+		put_pcichild(hpdev, hv_pcidev_ref_by_slot);
+
+		ret = vmbus_sendpacket(
+			hdev->channel, &pkt->message,
+			sizeof(*res_assigned),
+			(unsigned long)pkt,
+			VM_PKT_DATA_INBAND,
+			VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
+		if (ret)
+			break;
+
+		wait_for_completion(&comp_pkt.host_event);
+
+		if (comp_pkt.completion_status < 0) {
+			ret = -EPROTO;
+			dev_err(&hdev->device,
+				"resource allocated returned 0x%x",
+				comp_pkt.completion_status);
+			break;
+		}
+	}
+
+	kfree(pkt);
+	return ret;
+}
+
+/**
+ * hv_send_resources_released() - Report local resources
+ * released
+ * @hdev:	VMBus's tracking struct for this root PCI bus
+ *
+ * Return: 0 on success, -errno on failure
+ */
+static int hv_send_resources_released(struct hv_device *hdev)
+{
+	struct hv_pcibus_device *hbus = hv_get_drvdata(hdev);
+	struct pci_child_message pkt;
+	struct hv_pci_dev *hpdev;
+	u32 wslot;
+	int ret;
+
+	for (wslot = 0; wslot < 256; wslot++) {
+		hpdev = get_pcichild_wslot(hbus, wslot);
+		if (!hpdev)
+			continue;
+
+		memset(&pkt, 0, sizeof(pkt));
+		pkt.message_type = PCI_RESOURCES_RELEASED;
+		pkt.wslot.slot = hpdev->desc.win_slot.slot;
+
+		put_pcichild(hpdev, hv_pcidev_ref_by_slot);
+
+		ret = vmbus_sendpacket(hdev->channel, &pkt, sizeof(pkt), 0,
+				       VM_PKT_DATA_INBAND, 0);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
+static void get_hvpcibus(struct hv_pcibus_device *hbus)
+{
+	atomic_inc(&hbus->remove_lock);
+}
+
+static void put_hvpcibus(struct hv_pcibus_device *hbus)
+{
+	if (atomic_dec_and_test(&hbus->remove_lock))
+		complete(&hbus->remove_event);
+}
+
+/**
+ * hv_pci_probe() - New VMBus channel probe, for a root PCI bus
+ * @hdev:	VMBus's tracking struct for this root PCI bus
+ * @dev_id:	Identifies the device itself
+ *
+ * Return: 0 on success, -errno on failure
+ */
+static int hv_pci_probe(struct hv_device *hdev,
+			const struct hv_vmbus_device_id *dev_id)
+{
+	struct hv_pcibus_device *hbus;
+	int ret;
+
+	hbus = kzalloc(sizeof(*hbus), GFP_KERNEL);
+	if (!hbus)
+		return -ENOMEM;
+
+	/*
+	 * The PCI bus "domain" is what is called "segment" in ACPI and
+	 * other specs.  Pull it from the instance ID, to get something
+	 * unique.  Bytes 8 and 9 are what is used in Windows guests, so
+	 * do the same thing for consistency.  Note that, since this code
+	 * only runs in a Hyper-V VM, Hyper-V can (and does) guarantee
+	 * that (1) the only domain in use for something that looks like
+	 * a physical PCI bus (which is actually emulated by the
+	 * hypervisor) is domain 0 and (2) there will be no overlap
+	 * between domains derived from these instance IDs in the same
+	 * VM.
+	 */
+
+	hbus->sysdata.domain = hdev->dev_instance.b[9] |
+			       hdev->dev_instance.b[8] << 8;
+
+	hbus->hdev = hdev;
+	atomic_inc(&hbus->remove_lock);
+	INIT_LIST_HEAD(&hbus->children);
+	INIT_LIST_HEAD(&hbus->dr_list);
+	INIT_LIST_HEAD(&hbus->resources_for_children);
+	spin_lock_init(&hbus->config_lock);
+	spin_lock_init(&hbus->device_list_lock);
+	sema_init(&hbus->enum_sem, 1);
+	init_completion(&hbus->remove_event);
+
+	ret = vmbus_open(hdev->channel, pci_ring_size, pci_ring_size, NULL, 0,
+			 hv_pci_onchannelcallback, hbus);
+	if (ret)
+		goto free_bus;
+
+	hv_set_drvdata(hdev, hbus);
+
+	ret = hv_pci_protocol_negotiation(hdev);
+	if (ret)
+		goto close;
+
+	ret = hv_allocate_config_window(hbus);
+	if (ret)
+		goto close;
+
+	hbus->cfg_addr = ioremap(hbus->mem_config->start,
+				 PCI_CONFIG_MMIO_LENGTH);
+	if (!hbus->cfg_addr) {
+		dev_err(&hdev->device,
+			"Unable to map a virtual address for config space\n");
+		ret = -ENOMEM;
+		goto free_config;
+	}
+
+	hbus->sysdata.fwnode = irq_domain_alloc_fwnode(hbus);
+	if (!hbus->sysdata.fwnode) {
+		ret = -ENOMEM;
+		goto unmap;
+	}
+
+	ret = hv_pcie_init_irq_domain(hbus);
+	if (ret)
+		goto free_fwnode;
+
+	ret = hv_pci_query_relations(hdev);
+	if (ret)
+		goto free_irq_domain;
+
+	ret = hv_pci_enter_d0(hdev);
+	if (ret)
+		goto free_irq_domain;
+
+	ret = hv_pci_allocate_bridge_windows(hbus);
+	if (ret)
+		goto free_irq_domain;
+
+	ret = hv_send_resources_allocated(hdev);
+	if (ret)
+		goto free_windows;
+
+	prepopulate_bars(hbus);
+
+	hbus->state = hv_pcibus_probed;
+
+	ret = create_root_hv_pci_bus(hbus);
+	if (ret)
+		goto free_windows;
+
+	return 0;
+
+free_windows:
+	hv_pci_free_bridge_windows(hbus);
+free_irq_domain:
+	irq_domain_remove(hbus->irq_domain);
+free_fwnode:
+	irq_domain_free_fwnode(hbus->sysdata.fwnode);
+unmap:
+	iounmap(hbus->cfg_addr);
+free_config:
+	hv_free_config_window(hbus);
+close:
+	vmbus_close(hdev->channel);
+free_bus:
+	kfree(hbus);
+	return ret;
+}
+
+/**
+ * hv_pci_remove() - Remove routine for this VMBus channel
+ * @hdev:	VMBus's tracking struct for this root PCI bus
+ *
+ * Return: 0 on success, -errno on failure
+ */
+static int hv_pci_remove(struct hv_device *hdev)
+{
+	int ret;
+	struct hv_pcibus_device *hbus;
+	union {
+		struct pci_packet teardown_packet;
+		u8 buffer[0x100];
+	} pkt;
+	struct pci_bus_relations relations;
+	struct hv_pci_compl comp_pkt;
+
+	hbus = hv_get_drvdata(hdev);
+
+	ret = hv_send_resources_released(hdev);
+	if (ret)
+		dev_err(&hdev->device,
+			"Couldn't send resources released packet(s)\n");
+
+	memset(&pkt.teardown_packet, 0, sizeof(pkt.teardown_packet));
+	init_completion(&comp_pkt.host_event);
+	pkt.teardown_packet.completion_func = hv_pci_generic_compl;
+	pkt.teardown_packet.compl_ctxt = &comp_pkt;
+	pkt.teardown_packet.message.message_type = PCI_BUS_D0EXIT;
+
+	ret = vmbus_sendpacket(hdev->channel, &pkt.teardown_packet.message,
+			       sizeof(struct pci_message),
+			       (unsigned long)&pkt.teardown_packet,
+			       VM_PKT_DATA_INBAND,
+			       VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
+	if (!ret)
+		wait_for_completion_timeout(&comp_pkt.host_event, 10 * HZ);
+
+	if (hbus->state == hv_pcibus_installed) {
+		/* Remove the bus from PCI's point of view. */
+		pci_lock_rescan_remove();
+		pci_stop_root_bus(hbus->pci_bus);
+		pci_remove_root_bus(hbus->pci_bus);
+		pci_unlock_rescan_remove();
+	}
+
+	vmbus_close(hdev->channel);
+
+	/* Delete any children which might still exist. */
+	memset(&relations, 0, sizeof(relations));
+	hv_pci_devices_present(hbus, &relations);
+
+	iounmap(hbus->cfg_addr);
+	hv_free_config_window(hbus);
+	pci_free_resource_list(&hbus->resources_for_children);
+	hv_pci_free_bridge_windows(hbus);
+	irq_domain_remove(hbus->irq_domain);
+	irq_domain_free_fwnode(hbus->sysdata.fwnode);
+	put_hvpcibus(hbus);
+	wait_for_completion(&hbus->remove_event);
+	kfree(hbus);
+	return 0;
+}
+
+static const struct hv_vmbus_device_id hv_pci_id_table[] = {
+	/* PCI Pass-through Class ID */
+	/* 44C4F61D-4444-4400-9D52-802E27EDE19F */
+	{ HV_PCIE_GUID, },
+	{ },
+};
+
+MODULE_DEVICE_TABLE(vmbus, hv_pci_id_table);
+
+static struct hv_driver hv_pci_drv = {
+	.name		= "hv_pci",
+	.id_table	= hv_pci_id_table,
+	.probe		= hv_pci_probe,
+	.remove		= hv_pci_remove,
+};
+
+static void __exit exit_hv_pci_drv(void)
+{
+	vmbus_driver_unregister(&hv_pci_drv);
+}
+
+static int __init init_hv_pci_drv(void)
+{
+	return vmbus_driver_register(&hv_pci_drv);
+}
+
+module_init(init_hv_pci_drv);
+module_exit(exit_hv_pci_drv);
+
+MODULE_DESCRIPTION("Hyper-V PCI");
+MODULE_LICENSE("GPL v2");
