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153 lines
5.6 KiB
C
153 lines
5.6 KiB
C
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/*
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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.txt 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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/*
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* hmm_pfn_t - HMM uses its own pfn type to keep several flags per page
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*
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* Flags:
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* HMM_PFN_VALID: pfn is valid
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* HMM_PFN_WRITE: CPU page table has write permission set
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*/
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typedef unsigned long hmm_pfn_t;
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#define HMM_PFN_VALID (1 << 0)
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#define HMM_PFN_WRITE (1 << 1)
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#define HMM_PFN_SHIFT 2
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/*
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* hmm_pfn_t_to_page() - return struct page pointed to by a valid hmm_pfn_t
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* @pfn: hmm_pfn_t to convert to struct page
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* Returns: struct page pointer if pfn is a valid hmm_pfn_t, NULL otherwise
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*
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* If the hmm_pfn_t is valid (ie valid flag set) then return the struct page
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* matching the pfn value stored in the hmm_pfn_t. Otherwise return NULL.
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*/
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static inline struct page *hmm_pfn_t_to_page(hmm_pfn_t pfn)
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{
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if (!(pfn & HMM_PFN_VALID))
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return NULL;
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return pfn_to_page(pfn >> HMM_PFN_SHIFT);
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}
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/*
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* hmm_pfn_t_to_pfn() - return pfn value store in a hmm_pfn_t
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* @pfn: hmm_pfn_t to extract pfn from
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* Returns: pfn value if hmm_pfn_t is valid, -1UL otherwise
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*/
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static inline unsigned long hmm_pfn_t_to_pfn(hmm_pfn_t pfn)
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{
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if (!(pfn & HMM_PFN_VALID))
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return -1UL;
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return (pfn >> HMM_PFN_SHIFT);
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}
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/*
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* hmm_pfn_t_from_page() - create a valid hmm_pfn_t value from struct page
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* @page: struct page pointer for which to create the hmm_pfn_t
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* Returns: valid hmm_pfn_t for the page
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*/
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static inline hmm_pfn_t hmm_pfn_t_from_page(struct page *page)
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{
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return (page_to_pfn(page) << HMM_PFN_SHIFT) | HMM_PFN_VALID;
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}
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/*
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* hmm_pfn_t_from_pfn() - create a valid hmm_pfn_t value from pfn
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* @pfn: pfn value for which to create the hmm_pfn_t
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* Returns: valid hmm_pfn_t for the pfn
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*/
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static inline hmm_pfn_t hmm_pfn_t_from_pfn(unsigned long pfn)
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{
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return (pfn << HMM_PFN_SHIFT) | HMM_PFN_VALID;
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}
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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) */
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/* Below are for HMM internal use only! Not to be used by device driver! */
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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) */
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#endif /* LINUX_HMM_H */
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