mm/hmm: heterogeneous memory management (HMM for short)

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 <jglisse@redhat.com>
Signed-off-by: Evgeny Baskakov <ebaskakov@nvidia.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Mark Hairgrove <mhairgrove@nvidia.com>
Signed-off-by: Sherry Cheung <SCheung@nvidia.com>
Signed-off-by: Subhash Gutti <sgutti@nvidia.com>
Cc: Aneesh Kumar <aneesh.kumar@linux.vnet.ibm.com>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: David Nellans <dnellans@nvidia.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Bob Liu <liubo95@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

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 <jglisse@redhat.com>
+ */
+/*
+ * 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 <linux/kconfig.h>
+
+#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 */