565 lines
20 KiB
C
565 lines
20 KiB
C
/*
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* Copyright 2013 Red Hat Inc.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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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 range of the CPU page
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* table 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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#if IS_ENABLED(CONFIG_HMM)
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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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struct hmm;
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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 provide a flags array, if driver valid bit for an entry is bit
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* 3 ie (entry & (1 << 3)) is true if entry is valid then 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 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 vm_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 provide entry value for none entry, error entry and special entry,
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* driver can alias (ie use same value for error and special for instance). It
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* should not alias none and 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
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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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* @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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* @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 vm_area_struct *vma;
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struct list_head list;
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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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uint8_t pfn_shift;
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bool valid;
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};
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/*
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* hmm_pfn_to_page() - return struct page pointed to by a valid HMM pfn
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* @range: range use to decode HMM pfn value
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* @pfn: HMM pfn value to get corresponding struct page from
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* Returns: struct page pointer if pfn is a valid HMM pfn, NULL otherwise
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*
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* If the HMM pfn is valid (ie valid flag set) then return the struct page
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* matching the pfn value stored in the HMM pfn. Otherwise return NULL.
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*/
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static inline struct page *hmm_pfn_to_page(const struct hmm_range *range,
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uint64_t pfn)
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{
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if (pfn == range->values[HMM_PFN_NONE])
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return NULL;
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if (pfn == range->values[HMM_PFN_ERROR])
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return NULL;
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if (pfn == range->values[HMM_PFN_SPECIAL])
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return NULL;
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if (!(pfn & range->flags[HMM_PFN_VALID]))
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return NULL;
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return pfn_to_page(pfn >> range->pfn_shift);
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}
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/*
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* hmm_pfn_to_pfn() - return pfn value store in a HMM pfn
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* @range: range use to decode HMM pfn value
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* @pfn: HMM pfn value to extract pfn from
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* Returns: pfn value if HMM pfn is valid, -1UL otherwise
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*/
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static inline unsigned long hmm_pfn_to_pfn(const struct hmm_range *range,
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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_pfn_from_page() - create a valid HMM pfn value from struct page
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* @range: range use to encode HMM pfn value
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* @page: struct page pointer for which to create the HMM pfn
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* Returns: valid HMM pfn for the page
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*/
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static inline uint64_t hmm_pfn_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_pfn_from_pfn() - create a valid HMM pfn 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 HMM pfn
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* Returns: valid HMM pfn for the pfn
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*/
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static inline uint64_t hmm_pfn_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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#if IS_ENABLED(CONFIG_HMM_MIRROR)
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/*
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* Mirroring: how to synchronize device page table with CPU page table.
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*
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* A device driver that is participating in HMM mirroring must always
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* synchronize with CPU page table updates. For this, device drivers can either
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* directly use mmu_notifier APIs or they can use the hmm_mirror API. Device
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* drivers can decide to register one mirror per device per process, or just
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* one mirror per process for a group of devices. The pattern is:
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*
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* int device_bind_address_space(..., struct mm_struct *mm, ...)
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* {
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* struct device_address_space *das;
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*
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* // Device driver specific initialization, and allocation of das
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* // which contains an hmm_mirror struct as one of its fields.
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* ...
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*
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* ret = hmm_mirror_register(&das->mirror, mm, &device_mirror_ops);
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* if (ret) {
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* // Cleanup on error
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* return ret;
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* }
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*
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* // Other device driver specific initialization
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* ...
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* }
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*
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* Once an hmm_mirror is registered for an address space, the device driver
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* will get callbacks through sync_cpu_device_pagetables() operation (see
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* hmm_mirror_ops struct).
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*
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* Device driver must not free the struct containing the hmm_mirror struct
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* before calling hmm_mirror_unregister(). The expected usage is to do that when
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* the device driver is unbinding from an address space.
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*
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*
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* void device_unbind_address_space(struct device_address_space *das)
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* {
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* // Device driver specific cleanup
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* ...
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*
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* hmm_mirror_unregister(&das->mirror);
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*
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* // Other device driver specific cleanup, and now das can be freed
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* ...
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* }
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*/
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struct hmm_mirror;
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/*
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* enum hmm_update_type - type of update
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* @HMM_UPDATE_INVALIDATE: invalidate range (no indication as to why)
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*/
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enum hmm_update_type {
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HMM_UPDATE_INVALIDATE,
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};
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/*
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* struct hmm_mirror_ops - HMM mirror device operations callback
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*
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* @update: callback to update range on a device
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*/
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struct hmm_mirror_ops {
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/* release() - release hmm_mirror
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*
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* @mirror: pointer to struct hmm_mirror
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*
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* This is called when the mm_struct is being released.
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* The callback should make sure no references to the mirror occur
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* after the callback returns.
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*/
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void (*release)(struct hmm_mirror *mirror);
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/* sync_cpu_device_pagetables() - synchronize page tables
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*
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* @mirror: pointer to struct hmm_mirror
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* @update_type: type of update that occurred to the CPU page table
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* @start: virtual start address of the range to update
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* @end: virtual end address of the range to update
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*
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* This callback ultimately originates from mmu_notifiers when the CPU
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* page table is updated. The device driver must update its page table
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* in response to this callback. The update argument tells what action
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* to perform.
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*
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* The device driver must not return from this callback until the device
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* page tables are completely updated (TLBs flushed, etc); this is a
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* synchronous call.
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*/
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void (*sync_cpu_device_pagetables)(struct hmm_mirror *mirror,
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enum hmm_update_type update_type,
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unsigned long start,
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unsigned long end);
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};
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/*
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* struct hmm_mirror - mirror struct for a device driver
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*
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* @hmm: pointer to struct hmm (which is unique per mm_struct)
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* @ops: device driver callback for HMM mirror operations
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* @list: for list of mirrors of a given mm
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*
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* Each address space (mm_struct) being mirrored by a device must register one
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* instance of an hmm_mirror struct with HMM. HMM will track the list of all
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* mirrors for each mm_struct.
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*/
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struct hmm_mirror {
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struct hmm *hmm;
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const struct hmm_mirror_ops *ops;
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struct list_head list;
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};
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int hmm_mirror_register(struct hmm_mirror *mirror, struct mm_struct *mm);
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void hmm_mirror_unregister(struct hmm_mirror *mirror);
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/*
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* To snapshot the CPU page table, call hmm_vma_get_pfns(), then take a device
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* driver lock that serializes device page table updates, then call
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* hmm_vma_range_done(), to check if the snapshot is still valid. The same
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* device driver page table update lock must also be used in the
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* hmm_mirror_ops.sync_cpu_device_pagetables() callback, so that CPU page
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* table invalidation serializes on it.
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*
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* YOU MUST CALL hmm_vma_range_done() ONCE AND ONLY ONCE EACH TIME YOU CALL
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* hmm_vma_get_pfns() WITHOUT ERROR !
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*
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* IF YOU DO NOT FOLLOW THE ABOVE RULE THE SNAPSHOT CONTENT MIGHT BE INVALID !
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*/
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int hmm_vma_get_pfns(struct hmm_range *range);
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bool hmm_vma_range_done(struct hmm_range *range);
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/*
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* Fault memory on behalf of device driver. Unlike handle_mm_fault(), this will
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* not migrate any device memory back to system memory. The HMM pfn array will
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* be updated with the fault result and current snapshot of the CPU page table
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* for the range.
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*
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* The mmap_sem must be taken in read mode before entering and it might be
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* dropped by the function if the block argument is false. In that case, the
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* function returns -EAGAIN.
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*
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* Return value does not reflect if the fault was successful for every single
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* address or not. Therefore, the caller must to inspect the HMM pfn array to
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* determine fault status for each address.
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*
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* Trying to fault inside an invalid vma will result in -EINVAL.
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*
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* See the function description in mm/hmm.c for further documentation.
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*/
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int hmm_vma_fault(struct hmm_range *range, bool block);
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/* Below are for HMM internal use only! Not to be used by device driver! */
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void hmm_mm_destroy(struct mm_struct *mm);
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static inline void hmm_mm_init(struct mm_struct *mm)
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{
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mm->hmm = NULL;
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}
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#else /* IS_ENABLED(CONFIG_HMM_MIRROR) */
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static inline void hmm_mm_destroy(struct mm_struct *mm) {}
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static inline void hmm_mm_init(struct mm_struct *mm) {}
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#endif /* IS_ENABLED(CONFIG_HMM_MIRROR) */
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#if IS_ENABLED(CONFIG_DEVICE_PRIVATE) || IS_ENABLED(CONFIG_DEVICE_PUBLIC)
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struct hmm_devmem;
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struct page *hmm_vma_alloc_locked_page(struct vm_area_struct *vma,
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unsigned long addr);
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/*
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* struct hmm_devmem_ops - callback for ZONE_DEVICE memory events
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*
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* @free: call when refcount on page reach 1 and thus is no longer use
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* @fault: call when there is a page fault to unaddressable memory
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*
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* Both callback happens from page_free() and page_fault() callback of struct
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* dev_pagemap respectively. See include/linux/memremap.h for more details on
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* those.
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*
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* The hmm_devmem_ops callback are just here to provide a coherent and
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* uniq API to device driver and device driver should not register their
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* own page_free() or page_fault() but rely on the hmm_devmem_ops call-
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* back.
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*/
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struct hmm_devmem_ops {
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/*
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* free() - free a device page
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* @devmem: device memory structure (see struct hmm_devmem)
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* @page: pointer to struct page being freed
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*
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* Call back occurs whenever a device page refcount reach 1 which
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* means that no one is holding any reference on the page anymore
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* (ZONE_DEVICE page have an elevated refcount of 1 as default so
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* that they are not release to the general page allocator).
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*
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* Note that callback has exclusive ownership of the page (as no
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* one is holding any reference).
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*/
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void (*free)(struct hmm_devmem *devmem, struct page *page);
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/*
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* fault() - CPU page fault or get user page (GUP)
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* @devmem: device memory structure (see struct hmm_devmem)
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* @vma: virtual memory area containing the virtual address
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* @addr: virtual address that faulted or for which there is a GUP
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* @page: pointer to struct page backing virtual address (unreliable)
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* @flags: FAULT_FLAG_* (see include/linux/mm.h)
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* @pmdp: page middle directory
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* Returns: VM_FAULT_MINOR/MAJOR on success or one of VM_FAULT_ERROR
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* on error
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*
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* The callback occurs whenever there is a CPU page fault or GUP on a
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* virtual address. This means that the device driver must migrate the
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* page back to regular memory (CPU accessible).
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*
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* The device driver is free to migrate more than one page from the
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* fault() callback as an optimization. However if device decide to
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* migrate more than one page it must always priotirize the faulting
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* address over the others.
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*
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* The struct page pointer is only given as an hint to allow quick
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* lookup of internal device driver data. A concurrent migration
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* might have already free that page and the virtual address might
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* not longer be back by it. So it should not be modified by the
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* callback.
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*
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* Note that mmap semaphore is held in read mode at least when this
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* callback occurs, hence the vma is valid upon callback entry.
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*/
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int (*fault)(struct hmm_devmem *devmem,
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struct vm_area_struct *vma,
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unsigned long addr,
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const struct page *page,
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unsigned int flags,
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pmd_t *pmdp);
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};
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/*
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* struct hmm_devmem - track device memory
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*
|
||
* @completion: completion object for device memory
|
||
* @pfn_first: first pfn for this resource (set by hmm_devmem_add())
|
||
* @pfn_last: last pfn for this resource (set by hmm_devmem_add())
|
||
* @resource: IO resource reserved for this chunk of memory
|
||
* @pagemap: device page map for that chunk
|
||
* @device: device to bind resource to
|
||
* @ops: memory operations callback
|
||
* @ref: per CPU refcount
|
||
*
|
||
* This an helper structure for device drivers that do not wish to implement
|
||
* the gory details related to hotplugging new memoy and allocating struct
|
||
* pages.
|
||
*
|
||
* Device drivers can directly use ZONE_DEVICE memory on their own if they
|
||
* wish to do so.
|
||
*/
|
||
struct hmm_devmem {
|
||
struct completion completion;
|
||
unsigned long pfn_first;
|
||
unsigned long pfn_last;
|
||
struct resource *resource;
|
||
struct device *device;
|
||
struct dev_pagemap pagemap;
|
||
const struct hmm_devmem_ops *ops;
|
||
struct percpu_ref ref;
|
||
};
|
||
|
||
/*
|
||
* To add (hotplug) device memory, HMM assumes that there is no real resource
|
||
* that reserves a range in the physical address space (this is intended to be
|
||
* use by unaddressable device memory). It will reserve a physical range big
|
||
* enough and allocate struct page for it.
|
||
*
|
||
* The device driver can wrap the hmm_devmem struct inside a private device
|
||
* driver struct. The device driver must call hmm_devmem_remove() before the
|
||
* device goes away and before freeing the hmm_devmem struct memory.
|
||
*/
|
||
struct hmm_devmem *hmm_devmem_add(const struct hmm_devmem_ops *ops,
|
||
struct device *device,
|
||
unsigned long size);
|
||
struct hmm_devmem *hmm_devmem_add_resource(const struct hmm_devmem_ops *ops,
|
||
struct device *device,
|
||
struct resource *res);
|
||
void hmm_devmem_remove(struct hmm_devmem *devmem);
|
||
|
||
/*
|
||
* hmm_devmem_page_set_drvdata - set per-page driver data field
|
||
*
|
||
* @page: pointer to struct page
|
||
* @data: driver data value to set
|
||
*
|
||
* Because page can not be on lru we have an unsigned long that driver can use
|
||
* to store a per page field. This just a simple helper to do that.
|
||
*/
|
||
static inline void hmm_devmem_page_set_drvdata(struct page *page,
|
||
unsigned long data)
|
||
{
|
||
page->hmm_data = data;
|
||
}
|
||
|
||
/*
|
||
* hmm_devmem_page_get_drvdata - get per page driver data field
|
||
*
|
||
* @page: pointer to struct page
|
||
* Return: driver data value
|
||
*/
|
||
static inline unsigned long hmm_devmem_page_get_drvdata(const struct page *page)
|
||
{
|
||
return page->hmm_data;
|
||
}
|
||
|
||
|
||
/*
|
||
* struct hmm_device - fake device to hang device memory onto
|
||
*
|
||
* @device: device struct
|
||
* @minor: device minor number
|
||
*/
|
||
struct hmm_device {
|
||
struct device device;
|
||
unsigned int minor;
|
||
};
|
||
|
||
/*
|
||
* A device driver that wants to handle multiple devices memory through a
|
||
* single fake device can use hmm_device to do so. This is purely a helper and
|
||
* it is not strictly needed, in order to make use of any HMM functionality.
|
||
*/
|
||
struct hmm_device *hmm_device_new(void *drvdata);
|
||
void hmm_device_put(struct hmm_device *hmm_device);
|
||
#endif /* CONFIG_DEVICE_PRIVATE || CONFIG_DEVICE_PUBLIC */
|
||
#else /* IS_ENABLED(CONFIG_HMM) */
|
||
static inline void hmm_mm_destroy(struct mm_struct *mm) {}
|
||
static inline void hmm_mm_init(struct mm_struct *mm) {}
|
||
#endif /* IS_ENABLED(CONFIG_HMM) */
|
||
|
||
#endif /* LINUX_HMM_H */
|