diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 43dc35fe5bc0..969cde5d74c8 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3949,6 +3949,12 @@
 				please report a bug.
 		nocrs		[X86] Ignore PCI host bridge windows from ACPI.
 				If you need to use this, please report a bug.
+		use_e820	[X86] Honor E820 reservations when allocating
+				PCI host bridge memory. If you need to use this,
+				please report a bug.
+		no_e820		[X86] ignore E820 reservations when allocating
+				PCI host bridge memory. If you need to use this,
+				please report a bug.
 		routeirq	Do IRQ routing for all PCI devices.
 				This is normally done in pci_enable_device(),
 				so this option is a temporary workaround
diff --git a/arch/x86/include/asm/pci_x86.h b/arch/x86/include/asm/pci_x86.h
index 490411dba438..e45d661f81de 100644
--- a/arch/x86/include/asm/pci_x86.h
+++ b/arch/x86/include/asm/pci_x86.h
@@ -39,6 +39,8 @@ do {						\
 #define PCI_ROOT_NO_CRS		0x100000
 #define PCI_NOASSIGN_BARS	0x200000
 #define PCI_BIG_ROOT_WINDOW	0x400000
+#define PCI_USE_E820		0x800000
+#define PCI_NO_E820		0x1000000
 
 extern unsigned int pci_probe;
 extern unsigned long pirq_table_addr;
@@ -64,6 +66,8 @@ void pcibios_scan_specific_bus(int busn);
 
 /* pci-irq.c */
 
+struct pci_dev;
+
 struct irq_info {
 	u8 bus, devfn;			/* Bus, device and function */
 	struct {
@@ -232,3 +236,9 @@ static inline void mmio_config_writel(void __iomem *pos, u32 val)
 # define x86_default_pci_init_irq	NULL
 # define x86_default_pci_fixup_irqs	NULL
 #endif
+
+#if defined CONFIG_PCI && defined CONFIG_ACPI
+extern bool pci_use_e820;
+#else
+#define pci_use_e820 false
+#endif
diff --git a/arch/x86/kernel/resource.c b/arch/x86/kernel/resource.c
index 9b9fb7882c20..e8dc9bc327bd 100644
--- a/arch/x86/kernel/resource.c
+++ b/arch/x86/kernel/resource.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <linux/ioport.h>
 #include <asm/e820/api.h>
+#include <asm/pci_x86.h>
 
 static void resource_clip(struct resource *res, resource_size_t start,
 			  resource_size_t end)
@@ -28,6 +29,9 @@ static void remove_e820_regions(struct resource *avail)
 	int i;
 	struct e820_entry *entry;
 
+	if (!pci_use_e820)
+		return;
+
 	for (i = 0; i < e820_table->nr_entries; i++) {
 		entry = &e820_table->entries[i];
 
diff --git a/arch/x86/pci/acpi.c b/arch/x86/pci/acpi.c
index 948656069cdd..6c2febe84b6f 100644
--- a/arch/x86/pci/acpi.c
+++ b/arch/x86/pci/acpi.c
@@ -21,6 +21,8 @@ struct pci_root_info {
 
 static bool pci_use_crs = true;
 static bool pci_ignore_seg = false;
+/* Consumed in arch/x86/kernel/resource.c */
+bool pci_use_e820 = false;
 
 static int __init set_use_crs(const struct dmi_system_id *id)
 {
@@ -160,6 +162,33 @@ void __init pci_acpi_crs_quirks(void)
 	       "if necessary, use \"pci=%s\" and report a bug\n",
 	       pci_use_crs ? "Using" : "Ignoring",
 	       pci_use_crs ? "nocrs" : "use_crs");
+
+	/*
+	 * Some BIOS-es contain a bug where they add addresses which map to system
+	 * RAM in the PCI bridge memory window returned by the ACPI _CRS method, see
+	 * commit 4dc2287c1805 ("x86: avoid E820 regions when allocating address space").
+	 * To avoid this Linux by default excludes E820 reservations when allocating
+	 * addresses since 2010. Windows however ignores E820 reserved regions for
+	 * PCI mem allocations, so in hindsight Linux honoring them is a problem.
+	 * In 2020 some systems have shown-up with E820 reservations which cover the
+	 * entire _CRS returned PCI bridge memory window, causing all attempts to
+	 * assign memory to PCI BARs to fail if Linux honors the E820 reservations.
+	 *
+	 * Ideally Linux would fully stop honoring E820 reservations for PCI mem
+	 * allocations, but then the old systems this was added for will regress.
+	 * Instead keep the old behavior for old systems, while ignoring the E820
+	 * reservations like Windows does for any systems from now on.
+	 */
+	if (year >= 0 && year < 2018)
+		pci_use_e820 = true;
+
+	if (pci_probe & PCI_NO_E820)
+		pci_use_e820 = false;
+	else if (pci_probe & PCI_USE_E820)
+		pci_use_e820 = true;
+
+	printk(KERN_INFO "PCI: %s E820 reservations for host bridge windows\n",
+	       pci_use_e820 ? "Honoring" : "Ignoring");
 }
 
 #ifdef	CONFIG_PCI_MMCONFIG
diff --git a/arch/x86/pci/common.c b/arch/x86/pci/common.c
index 3507f456fcd0..091ec7e94fcb 100644
--- a/arch/x86/pci/common.c
+++ b/arch/x86/pci/common.c
@@ -595,6 +595,12 @@ char *__init pcibios_setup(char *str)
 	} else if (!strcmp(str, "nocrs")) {
 		pci_probe |= PCI_ROOT_NO_CRS;
 		return NULL;
+	} else if (!strcmp(str, "use_e820")) {
+		pci_probe |= PCI_USE_E820;
+		return NULL;
+	} else if (!strcmp(str, "no_e820")) {
+		pci_probe |= PCI_NO_E820;
+		return NULL;
 #ifdef CONFIG_PHYS_ADDR_T_64BIT
 	} else if (!strcmp(str, "big_root_window")) {
 		pci_probe |= PCI_BIG_ROOT_WINDOW;
