@@ -3,58 +3,8 @@
* Copyright 2013 Red Hat Inc.
*
* Authors: Jérôme Glisse <jglisse@redhat.com>
- */
-/*
- * Heterogeneous Memory Management (HMM)
- *
- * See Documentation/vm/hmm.rst for reasons and overview of what HMM is and it
- * is for. Here we focus on the HMM API description, with some explanation of
- * the underlying implementation.
- *
- * Short description: HMM provides a set of helpers to share a virtual address
- * space between CPU and a device, so that the device can access any valid
- * address of the process (while still obeying memory protection). HMM also
- * provides helpers to migrate process memory to device memory, and back. Each
- * set of functionality (address space mirroring, and migration to and from
- * device memory) can be used independently of the other.
- *
- *
- * HMM address space mirroring API:
- *
- * Use HMM address space mirroring if you want to mirror a range of the CPU
- * page tables of a process into a device page table. Here, "mirror" means "keep
- * synchronized". Prerequisites: the device must provide the ability to write-
- * protect its page tables (at PAGE_SIZE granularity), and must be able to
- * recover from the resulting potential page faults.
*
- * HMM guarantees that at any point in time, a given virtual address points to
- * either the same memory in both CPU and device page tables (that is: CPU and
- * device page tables each point to the same pages), or that one page table (CPU
- * or device) points to no entry, while the other still points to the old page
- * for the address. The latter case happens when the CPU page table update
- * happens first, and then the update is mirrored over to the device page table.
- * This does not cause any issue, because the CPU page table cannot start
- * pointing to a new page until the device page table is invalidated.
- *
- * HMM uses mmu_notifiers to monitor the CPU page tables, and forwards any
- * updates to each device driver that has registered a mirror. It also provides
- * some API calls to help with taking a snapshot of the CPU page table, and to
- * synchronize with any updates that might happen concurrently.
- *
- *
- * HMM migration to and from device memory:
- *
- * HMM provides a set of helpers to hotplug device memory as ZONE_DEVICE, with
- * a new MEMORY_DEVICE_PRIVATE type. This provides a struct page for each page
- * of the device memory, and allows the device driver to manage its memory
- * using those struct pages. Having struct pages for device memory makes
- * migration easier. Because that memory is not addressable by the CPU it must
- * never be pinned to the device; in other words, any CPU page fault can always
- * cause the device memory to be migrated (copied/moved) back to regular memory.
- *
- * A new migrate helper (migrate_vma()) has been added (see mm/migrate.c) that
- * allows use of a device DMA engine to perform the copy operation between
- * regular system memory and device memory.
+ * See Documentation/vm/hmm.rst for reasons and overview of what HMM is.
*/
#ifndef LINUX_HMM_H
#define LINUX_HMM_H
@@ -120,9 +70,6 @@ enum hmm_pfn_value_e {
*
* @notifier: a mmu_interval_notifier that includes the start/end
* @notifier_seq: result of mmu_interval_read_begin()
- * @hmm: the core HMM structure this range is active against
- * @vma: the vm area struct for the range
- * @list: all range lock are on a list
* @start: range virtual start address (inclusive)
* @end: range virtual end address (exclusive)
* @pfns: array of pfns (big enough for the range)
@@ -130,8 +77,7 @@ enum hmm_pfn_value_e {
* @values: pfn value for some special case (none, special, error, ...)
* @default_flags: default flags for the range (write, read, ... see hmm doc)
* @pfn_flags_mask: allows to mask pfn flags so that only default_flags matter
- * @pfn_shifts: pfn shift value (should be <= PAGE_SHIFT)
- * @valid: pfns array did not change since it has been fill by an HMM function
+ * @pfn_shift: pfn shift value (should be <= PAGE_SHIFT)
* @dev_private_owner: owner of device private pages
*/
struct hmm_range {
@@ -171,52 +117,6 @@ static inline struct page *hmm_device_entry_to_page(const struct hmm_range *rang
return pfn_to_page(entry >> range->pfn_shift);
}
-/*
- * hmm_device_entry_to_pfn() - return pfn value store in a device entry
- * @range: range use to decode device entry value
- * @entry: device entry to extract pfn from
- * Return: pfn value if device entry is valid, -1UL otherwise
- */
-static inline unsigned long
-hmm_device_entry_to_pfn(const struct hmm_range *range, uint64_t pfn)
-{
- if (pfn == range->values[HMM_PFN_NONE])
- return -1UL;
- if (pfn == range->values[HMM_PFN_ERROR])
- return -1UL;
- if (pfn == range->values[HMM_PFN_SPECIAL])
- return -1UL;
- if (!(pfn & range->flags[HMM_PFN_VALID]))
- return -1UL;
- return (pfn >> range->pfn_shift);
-}
-
-/*
- * hmm_device_entry_from_page() - create a valid device entry for a page
- * @range: range use to encode HMM pfn value
- * @page: page for which to create the device entry
- * Return: valid device entry for the page
- */
-static inline uint64_t hmm_device_entry_from_page(const struct hmm_range *range,
- struct page *page)
-{
- return (page_to_pfn(page) << range->pfn_shift) |
- range->flags[HMM_PFN_VALID];
-}
-
-/*
- * hmm_device_entry_from_pfn() - create a valid device entry value from pfn
- * @range: range use to encode HMM pfn value
- * @pfn: pfn value for which to create the device entry
- * Return: valid device entry for the pfn
- */
-static inline uint64_t hmm_device_entry_from_pfn(const struct hmm_range *range,
- unsigned long pfn)
-{
- return (pfn << range->pfn_shift) |
- range->flags[HMM_PFN_VALID];
-}
-
/* Don't fault in missing PTEs, just snapshot the current state. */
#define HMM_FAULT_SNAPSHOT (1 << 1)
@@ -38,6 +38,18 @@ enum {
HMM_NEED_ALL_BITS = HMM_NEED_FAULT | HMM_NEED_WRITE_FAULT,
};
+/*
+ * hmm_device_entry_from_pfn() - create a valid device entry value from pfn
+ * @range: range use to encode HMM pfn value
+ * @pfn: pfn value for which to create the device entry
+ * Return: valid device entry for the pfn
+ */
+static uint64_t hmm_device_entry_from_pfn(const struct hmm_range *range,
+ unsigned long pfn)
+{
+ return (pfn << range->pfn_shift) | range->flags[HMM_PFN_VALID];
+}
+
static int hmm_pfns_fill(unsigned long addr, unsigned long end,
struct hmm_range *range, enum hmm_pfn_value_e value)
{
@@ -544,7 +556,7 @@ static const struct mm_walk_ops hmm_walk_ops = {
/**
* hmm_range_fault - try to fault some address in a virtual address range
- * @range: range being faulted
+ * @range: argument structure
* @flags: HMM_FAULT_* flags
*
* Return: the number of valid pages in range->pfns[] (from range start
@@ -558,13 +570,11 @@ static const struct mm_walk_ops hmm_walk_ops = {
* only).
* -EBUSY: The range has been invalidated and the caller needs to wait for
* the invalidation to finish.
- * -EFAULT: Invalid (i.e., either no valid vma or it is illegal to access
- * that range) number of valid pages in range->pfns[] (from
- * range start address).
+ * -EFAULT: A page was requested to be valid and could not be made valid
+ * ie it has no backing VMA or it is illegal to access
*
- * This is similar to a regular CPU page fault except that it will not trigger
- * any memory migration if the memory being faulted is not accessible by CPUs
- * and caller does not ask for migration.
+ * This is similar to get_user_pages(), except that it can read the page tables
+ * without mutating them (ie causing faults).
*
* On error, for one virtual address in the range, the function will mark the
* corresponding HMM pfn entry with an error flag.