250 lines
9.1 KiB
C
250 lines
9.1 KiB
C
/* SPDX-License-Identifier: GPL-2.0-or-later */
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/*
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* Copyright 2013 Red Hat Inc.
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*
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* Authors: Jérôme Glisse <jglisse@redhat.com>
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*/
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/*
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* Heterogeneous Memory Management (HMM)
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*
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* See Documentation/vm/hmm.rst for reasons and overview of what HMM is and it
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* is for. Here we focus on the HMM API description, with some explanation of
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* the underlying implementation.
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*
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* Short description: HMM provides a set of helpers to share a virtual address
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* space between CPU and a device, so that the device can access any valid
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* address of the process (while still obeying memory protection). HMM also
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* provides helpers to migrate process memory to device memory, and back. Each
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* set of functionality (address space mirroring, and migration to and from
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* device memory) can be used independently of the other.
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*
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*
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* HMM address space mirroring API:
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*
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* Use HMM address space mirroring if you want to mirror a range of the CPU
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* page tables of a process into a device page table. Here, "mirror" means "keep
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* synchronized". Prerequisites: the device must provide the ability to write-
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* protect its page tables (at PAGE_SIZE granularity), and must be able to
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* recover from the resulting potential page faults.
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*
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* HMM guarantees that at any point in time, a given virtual address points to
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* either the same memory in both CPU and device page tables (that is: CPU and
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* device page tables each point to the same pages), or that one page table (CPU
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* or device) points to no entry, while the other still points to the old page
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* for the address. The latter case happens when the CPU page table update
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* happens first, and then the update is mirrored over to the device page table.
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* This does not cause any issue, because the CPU page table cannot start
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* pointing to a new page until the device page table is invalidated.
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*
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* HMM uses mmu_notifiers to monitor the CPU page tables, and forwards any
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* updates to each device driver that has registered a mirror. It also provides
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* some API calls to help with taking a snapshot of the CPU page table, and to
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* synchronize with any updates that might happen concurrently.
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*
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*
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* HMM migration to and from device memory:
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*
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* HMM provides a set of helpers to hotplug device memory as ZONE_DEVICE, with
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* a new MEMORY_DEVICE_PRIVATE type. This provides a struct page for each page
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* of the device memory, and allows the device driver to manage its memory
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* using those struct pages. Having struct pages for device memory makes
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* migration easier. Because that memory is not addressable by the CPU it must
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* never be pinned to the device; in other words, any CPU page fault can always
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* cause the device memory to be migrated (copied/moved) back to regular memory.
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*
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* A new migrate helper (migrate_vma()) has been added (see mm/migrate.c) that
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* allows use of a device DMA engine to perform the copy operation between
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* regular system memory and device memory.
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*/
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#ifndef LINUX_HMM_H
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#define LINUX_HMM_H
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#include <linux/kconfig.h>
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#include <asm/pgtable.h>
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#include <linux/device.h>
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#include <linux/migrate.h>
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#include <linux/memremap.h>
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#include <linux/completion.h>
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#include <linux/mmu_notifier.h>
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/*
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* hmm_pfn_flag_e - HMM flag enums
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*
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* Flags:
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* HMM_PFN_VALID: pfn is valid. It has, at least, read permission.
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* HMM_PFN_WRITE: CPU page table has write permission set
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* HMM_PFN_DEVICE_PRIVATE: private device memory (ZONE_DEVICE)
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*
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* The driver provides a flags array for mapping page protections to device
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* PTE bits. If the driver valid bit for an entry is bit 3,
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* i.e., (entry & (1 << 3)), then the driver must provide
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* an array in hmm_range.flags with hmm_range.flags[HMM_PFN_VALID] == 1 << 3.
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* Same logic apply to all flags. This is the same idea as vm_page_prot in vma
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* except that this is per device driver rather than per architecture.
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*/
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enum hmm_pfn_flag_e {
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HMM_PFN_VALID = 0,
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HMM_PFN_WRITE,
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HMM_PFN_DEVICE_PRIVATE,
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HMM_PFN_FLAG_MAX
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};
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/*
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* hmm_pfn_value_e - HMM pfn special value
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*
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* Flags:
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* HMM_PFN_ERROR: corresponding CPU page table entry points to poisoned memory
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* HMM_PFN_NONE: corresponding CPU page table entry is pte_none()
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* HMM_PFN_SPECIAL: corresponding CPU page table entry is special; i.e., the
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* result of vmf_insert_pfn() or vm_insert_page(). Therefore, it should not
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* be mirrored by a device, because the entry will never have HMM_PFN_VALID
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* set and the pfn value is undefined.
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*
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* Driver provides values for none entry, error entry, and special entry.
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* Driver can alias (i.e., use same value) error and special, but
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* it should not alias none with error or special.
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*
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* HMM pfn value returned by hmm_vma_get_pfns() or hmm_vma_fault() will be:
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* hmm_range.values[HMM_PFN_ERROR] if CPU page table entry is poisonous,
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* hmm_range.values[HMM_PFN_NONE] if there is no CPU page table entry,
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* hmm_range.values[HMM_PFN_SPECIAL] if CPU page table entry is a special one
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*/
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enum hmm_pfn_value_e {
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HMM_PFN_ERROR,
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HMM_PFN_NONE,
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HMM_PFN_SPECIAL,
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HMM_PFN_VALUE_MAX
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};
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/*
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* struct hmm_range - track invalidation lock on virtual address range
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*
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* @notifier: a mmu_interval_notifier that includes the start/end
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* @notifier_seq: result of mmu_interval_read_begin()
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* @hmm: the core HMM structure this range is active against
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* @vma: the vm area struct for the range
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* @list: all range lock are on a list
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* @start: range virtual start address (inclusive)
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* @end: range virtual end address (exclusive)
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* @pfns: array of pfns (big enough for the range)
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* @flags: pfn flags to match device driver page table
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* @values: pfn value for some special case (none, special, error, ...)
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* @default_flags: default flags for the range (write, read, ... see hmm doc)
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* @pfn_flags_mask: allows to mask pfn flags so that only default_flags matter
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* @pfn_shifts: pfn shift value (should be <= PAGE_SHIFT)
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* @valid: pfns array did not change since it has been fill by an HMM function
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*/
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struct hmm_range {
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struct mmu_interval_notifier *notifier;
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unsigned long notifier_seq;
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unsigned long start;
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unsigned long end;
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uint64_t *pfns;
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const uint64_t *flags;
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const uint64_t *values;
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uint64_t default_flags;
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uint64_t pfn_flags_mask;
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uint8_t pfn_shift;
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};
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/*
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* hmm_device_entry_to_page() - return struct page pointed to by a device entry
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* @range: range use to decode device entry value
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* @entry: device entry value to get corresponding struct page from
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* Return: struct page pointer if entry is a valid, NULL otherwise
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*
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* If the device entry is valid (ie valid flag set) then return the struct page
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* matching the entry value. Otherwise return NULL.
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*/
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static inline struct page *hmm_device_entry_to_page(const struct hmm_range *range,
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uint64_t entry)
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{
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if (entry == range->values[HMM_PFN_NONE])
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return NULL;
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if (entry == range->values[HMM_PFN_ERROR])
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return NULL;
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if (entry == range->values[HMM_PFN_SPECIAL])
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return NULL;
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if (!(entry & range->flags[HMM_PFN_VALID]))
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return NULL;
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return pfn_to_page(entry >> range->pfn_shift);
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}
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/*
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* hmm_device_entry_to_pfn() - return pfn value store in a device entry
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* @range: range use to decode device entry value
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* @entry: device entry to extract pfn from
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* Return: pfn value if device entry is valid, -1UL otherwise
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*/
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static inline unsigned long
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hmm_device_entry_to_pfn(const struct hmm_range *range, uint64_t pfn)
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{
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if (pfn == range->values[HMM_PFN_NONE])
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return -1UL;
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if (pfn == range->values[HMM_PFN_ERROR])
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return -1UL;
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if (pfn == range->values[HMM_PFN_SPECIAL])
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return -1UL;
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if (!(pfn & range->flags[HMM_PFN_VALID]))
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return -1UL;
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return (pfn >> range->pfn_shift);
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}
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/*
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* hmm_device_entry_from_page() - create a valid device entry for a page
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* @range: range use to encode HMM pfn value
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* @page: page for which to create the device entry
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* Return: valid device entry for the page
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*/
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static inline uint64_t hmm_device_entry_from_page(const struct hmm_range *range,
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struct page *page)
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{
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return (page_to_pfn(page) << range->pfn_shift) |
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range->flags[HMM_PFN_VALID];
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}
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/*
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* hmm_device_entry_from_pfn() - create a valid device entry value from pfn
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* @range: range use to encode HMM pfn value
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* @pfn: pfn value for which to create the device entry
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* Return: valid device entry for the pfn
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*/
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static inline uint64_t hmm_device_entry_from_pfn(const struct hmm_range *range,
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unsigned long pfn)
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{
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return (pfn << range->pfn_shift) |
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range->flags[HMM_PFN_VALID];
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}
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/*
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* Retry fault if non-blocking, drop mmap_sem and return -EAGAIN in that case.
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*/
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#define HMM_FAULT_ALLOW_RETRY (1 << 0)
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/* Don't fault in missing PTEs, just snapshot the current state. */
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#define HMM_FAULT_SNAPSHOT (1 << 1)
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#ifdef CONFIG_HMM_MIRROR
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/*
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* Please see Documentation/vm/hmm.rst for how to use the range API.
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*/
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long hmm_range_fault(struct hmm_range *range, unsigned int flags);
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#else
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static inline long hmm_range_fault(struct hmm_range *range, unsigned int flags)
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{
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return -EOPNOTSUPP;
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}
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#endif
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/*
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* HMM_RANGE_DEFAULT_TIMEOUT - default timeout (ms) when waiting for a range
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*
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* When waiting for mmu notifiers we need some kind of time out otherwise we
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* could potentialy wait for ever, 1000ms ie 1s sounds like a long time to
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* wait already.
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*/
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#define HMM_RANGE_DEFAULT_TIMEOUT 1000
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#endif /* LINUX_HMM_H */
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