From 133ff0eac95b7dc6edf89dc51bd139a0630bbae7 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?J=C3=A9r=C3=B4me=20Glisse?= Date: Fri, 8 Sep 2017 16:11:23 -0700 Subject: mm/hmm: heterogeneous memory management (HMM for short) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit HMM provides 3 separate types of functionality: - Mirroring: synchronize CPU page table and device page table - Device memory: allocating struct page for device memory - Migration: migrating regular memory to device memory This patch introduces some common helpers and definitions to all of those 3 functionality. Link: http://lkml.kernel.org/r/20170817000548.32038-3-jglisse@redhat.com Signed-off-by: Jérôme Glisse Signed-off-by: Evgeny Baskakov Signed-off-by: John Hubbard Signed-off-by: Mark Hairgrove Signed-off-by: Sherry Cheung Signed-off-by: Subhash Gutti Cc: Aneesh Kumar Cc: Balbir Singh Cc: Benjamin Herrenschmidt Cc: Dan Williams Cc: David Nellans Cc: Johannes Weiner Cc: Kirill A. Shutemov Cc: Michal Hocko Cc: Paul E. McKenney Cc: Ross Zwisler Cc: Vladimir Davydov Cc: Bob Liu Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/hmm.h | 152 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 152 insertions(+) create mode 100644 include/linux/hmm.h (limited to 'include/linux/hmm.h') diff --git a/include/linux/hmm.h b/include/linux/hmm.h new file mode 100644 index 000000000000..5d83fec6dfdd --- /dev/null +++ b/include/linux/hmm.h @@ -0,0 +1,152 @@ +/* + * Copyright 2013 Red Hat Inc. + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * Authors: Jérôme Glisse + */ +/* + * Heterogeneous Memory Management (HMM) + * + * See Documentation/vm/hmm.txt 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 range of the CPU page + * table 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. + */ +#ifndef LINUX_HMM_H +#define LINUX_HMM_H + +#include + +#if IS_ENABLED(CONFIG_HMM) + + +/* + * hmm_pfn_t - HMM uses its own pfn type to keep several flags per page + * + * Flags: + * HMM_PFN_VALID: pfn is valid + * HMM_PFN_WRITE: CPU page table has write permission set + */ +typedef unsigned long hmm_pfn_t; + +#define HMM_PFN_VALID (1 << 0) +#define HMM_PFN_WRITE (1 << 1) +#define HMM_PFN_SHIFT 2 + +/* + * hmm_pfn_t_to_page() - return struct page pointed to by a valid hmm_pfn_t + * @pfn: hmm_pfn_t to convert to struct page + * Returns: struct page pointer if pfn is a valid hmm_pfn_t, NULL otherwise + * + * If the hmm_pfn_t is valid (ie valid flag set) then return the struct page + * matching the pfn value stored in the hmm_pfn_t. Otherwise return NULL. + */ +static inline struct page *hmm_pfn_t_to_page(hmm_pfn_t pfn) +{ + if (!(pfn & HMM_PFN_VALID)) + return NULL; + return pfn_to_page(pfn >> HMM_PFN_SHIFT); +} + +/* + * hmm_pfn_t_to_pfn() - return pfn value store in a hmm_pfn_t + * @pfn: hmm_pfn_t to extract pfn from + * Returns: pfn value if hmm_pfn_t is valid, -1UL otherwise + */ +static inline unsigned long hmm_pfn_t_to_pfn(hmm_pfn_t pfn) +{ + if (!(pfn & HMM_PFN_VALID)) + return -1UL; + return (pfn >> HMM_PFN_SHIFT); +} + +/* + * hmm_pfn_t_from_page() - create a valid hmm_pfn_t value from struct page + * @page: struct page pointer for which to create the hmm_pfn_t + * Returns: valid hmm_pfn_t for the page + */ +static inline hmm_pfn_t hmm_pfn_t_from_page(struct page *page) +{ + return (page_to_pfn(page) << HMM_PFN_SHIFT) | HMM_PFN_VALID; +} + +/* + * hmm_pfn_t_from_pfn() - create a valid hmm_pfn_t value from pfn + * @pfn: pfn value for which to create the hmm_pfn_t + * Returns: valid hmm_pfn_t for the pfn + */ +static inline hmm_pfn_t hmm_pfn_t_from_pfn(unsigned long pfn) +{ + return (pfn << HMM_PFN_SHIFT) | HMM_PFN_VALID; +} + + +/* Below are for HMM internal use only! Not to be used by device driver! */ +void hmm_mm_destroy(struct mm_struct *mm); + +static inline void hmm_mm_init(struct mm_struct *mm) +{ + mm->hmm = NULL; +} + +#else /* IS_ENABLED(CONFIG_HMM) */ + +/* Below are for HMM internal use only! Not to be used by device driver! */ +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 */ -- cgit v1.2.1