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Diffstat (limited to 'include/linux/hmm.h')
| -rw-r--r-- | include/linux/hmm.h | 520 |
1 files changed, 520 insertions, 0 deletions
diff --git a/include/linux/hmm.h b/include/linux/hmm.h new file mode 100644 index 000000000000..96e69979f84d --- /dev/null +++ b/include/linux/hmm.h @@ -0,0 +1,520 @@ +/* + * 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) + +#include <linux/device.h> +#include <linux/migrate.h> +#include <linux/memremap.h> +#include <linux/completion.h> + +struct 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_READ: CPU page table has read permission set + * HMM_PFN_WRITE: CPU page table has write permission set + * HMM_PFN_ERROR: corresponding CPU page table entry points to poisoned memory + * HMM_PFN_EMPTY: corresponding CPU page table entry is pte_none() + * HMM_PFN_SPECIAL: corresponding CPU page table entry is special; i.e., the + * result of vm_insert_pfn() or vm_insert_page(). Therefore, it should not + * be mirrored by a device, because the entry will never have HMM_PFN_VALID + * set and the pfn value is undefined. + * HMM_PFN_DEVICE_UNADDRESSABLE: unaddressable device memory (ZONE_DEVICE) + */ +typedef unsigned long hmm_pfn_t; + +#define HMM_PFN_VALID (1 << 0) +#define HMM_PFN_READ (1 << 1) +#define HMM_PFN_WRITE (1 << 2) +#define HMM_PFN_ERROR (1 << 3) +#define HMM_PFN_EMPTY (1 << 4) +#define HMM_PFN_SPECIAL (1 << 5) +#define HMM_PFN_DEVICE_UNADDRESSABLE (1 << 6) +#define HMM_PFN_SHIFT 7 + +/* + * 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; +} + + +#if IS_ENABLED(CONFIG_HMM_MIRROR) +/* + * Mirroring: how to synchronize device page table with CPU page table. + * + * A device driver that is participating in HMM mirroring must always + * synchronize with CPU page table updates. For this, device drivers can either + * directly use mmu_notifier APIs or they can use the hmm_mirror API. Device + * drivers can decide to register one mirror per device per process, or just + * one mirror per process for a group of devices. The pattern is: + * + * int device_bind_address_space(..., struct mm_struct *mm, ...) + * { + * struct device_address_space *das; + * + * // Device driver specific initialization, and allocation of das + * // which contains an hmm_mirror struct as one of its fields. + * ... + * + * ret = hmm_mirror_register(&das->mirror, mm, &device_mirror_ops); + * if (ret) { + * // Cleanup on error + * return ret; + * } + * + * // Other device driver specific initialization + * ... + * } + * + * Once an hmm_mirror is registered for an address space, the device driver + * will get callbacks through sync_cpu_device_pagetables() operation (see + * hmm_mirror_ops struct). + * + * Device driver must not free the struct containing the hmm_mirror struct + * before calling hmm_mirror_unregister(). The expected usage is to do that when + * the device driver is unbinding from an address space. + * + * + * void device_unbind_address_space(struct device_address_space *das) + * { + * // Device driver specific cleanup + * ... + * + * hmm_mirror_unregister(&das->mirror); + * + * // Other device driver specific cleanup, and now das can be freed + * ... + * } + */ + +struct hmm_mirror; + +/* + * enum hmm_update_type - type of update + * @HMM_UPDATE_INVALIDATE: invalidate range (no indication as to why) + */ +enum hmm_update_type { + HMM_UPDATE_INVALIDATE, +}; + +/* + * struct hmm_mirror_ops - HMM mirror device operations callback + * + * @update: callback to update range on a device + */ +struct hmm_mirror_ops { + /* sync_cpu_device_pagetables() - synchronize page tables + * + * @mirror: pointer to struct hmm_mirror + * @update_type: type of update that occurred to the CPU page table + * @start: virtual start address of the range to update + * @end: virtual end address of the range to update + * + * This callback ultimately originates from mmu_notifiers when the CPU + * page table is updated. The device driver must update its page table + * in response to this callback. The update argument tells what action + * to perform. + * + * The device driver must not return from this callback until the device + * page tables are completely updated (TLBs flushed, etc); this is a + * synchronous call. + */ + void (*sync_cpu_device_pagetables)(struct hmm_mirror *mirror, + enum hmm_update_type update_type, + unsigned long start, + unsigned long end); +}; + +/* + * struct hmm_mirror - mirror struct for a device driver + * + * @hmm: pointer to struct hmm (which is unique per mm_struct) + * @ops: device driver callback for HMM mirror operations + * @list: for list of mirrors of a given mm + * + * Each address space (mm_struct) being mirrored by a device must register one + * instance of an hmm_mirror struct with HMM. HMM will track the list of all + * mirrors for each mm_struct. + */ +struct hmm_mirror { + struct hmm *hmm; + const struct hmm_mirror_ops *ops; + struct list_head list; +}; + +int hmm_mirror_register(struct hmm_mirror *mirror, struct mm_struct *mm); +void hmm_mirror_unregister(struct hmm_mirror *mirror); + + +/* + * struct hmm_range - track invalidation lock on virtual address range + * + * @list: all range lock are on a list + * @start: range virtual start address (inclusive) + * @end: range virtual end address (exclusive) + * @pfns: array of pfns (big enough for the range) + * @valid: pfns array did not change since it has been fill by an HMM function + */ +struct hmm_range { + struct list_head list; + unsigned long start; + unsigned long end; + hmm_pfn_t *pfns; + bool valid; +}; + +/* + * To snapshot the CPU page table, call hmm_vma_get_pfns(), then take a device + * driver lock that serializes device page table updates, then call + * hmm_vma_range_done(), to check if the snapshot is still valid. The same + * device driver page table update lock must also be used in the + * hmm_mirror_ops.sync_cpu_device_pagetables() callback, so that CPU page + * table invalidation serializes on it. + * + * YOU MUST CALL hmm_vma_range_done() ONCE AND ONLY ONCE EACH TIME YOU CALL + * hmm_vma_get_pfns() WITHOUT ERROR ! + * + * IF YOU DO NOT FOLLOW THE ABOVE RULE THE SNAPSHOT CONTENT MIGHT BE INVALID ! + */ +int hmm_vma_get_pfns(struct vm_area_struct *vma, + struct hmm_range *range, + unsigned long start, + unsigned long end, + hmm_pfn_t *pfns); +bool hmm_vma_range_done(struct vm_area_struct *vma, struct hmm_range *range); + + +/* + * Fault memory on behalf of device driver. Unlike handle_mm_fault(), this will + * not migrate any device memory back to system memory. The hmm_pfn_t array will + * be updated with the fault result and current snapshot of the CPU page table + * for the range. + * + * The mmap_sem must be taken in read mode before entering and it might be + * dropped by the function if the block argument is false. In that case, the + * function returns -EAGAIN. + * + * Return value does not reflect if the fault was successful for every single + * address or not. Therefore, the caller must to inspect the hmm_pfn_t array to + * determine fault status for each address. + * + * Trying to fault inside an invalid vma will result in -EINVAL. + * + * See the function description in mm/hmm.c for further documentation. + */ +int hmm_vma_fault(struct vm_area_struct *vma, + struct hmm_range *range, + unsigned long start, + unsigned long end, + hmm_pfn_t *pfns, + bool write, + bool block); +#endif /* IS_ENABLED(CONFIG_HMM_MIRROR) */ + + +#if IS_ENABLED(CONFIG_DEVICE_PRIVATE) || IS_ENABLED(CONFIG_DEVICE_PUBLIC) +struct hmm_devmem; + +struct page *hmm_vma_alloc_locked_page(struct vm_area_struct *vma, + unsigned long addr); + +/* + * struct hmm_devmem_ops - callback for ZONE_DEVICE memory events + * + * @free: call when refcount on page reach 1 and thus is no longer use + * @fault: call when there is a page fault to unaddressable memory + * + * Both callback happens from page_free() and page_fault() callback of struct + * dev_pagemap respectively. See include/linux/memremap.h for more details on + * those. + * + * The hmm_devmem_ops callback are just here to provide a coherent and + * uniq API to device driver and device driver should not register their + * own page_free() or page_fault() but rely on the hmm_devmem_ops call- + * back. + */ +struct hmm_devmem_ops { + /* + * free() - free a device page + * @devmem: device memory structure (see struct hmm_devmem) + * @page: pointer to struct page being freed + * + * Call back occurs whenever a device page refcount reach 1 which + * means that no one is holding any reference on the page anymore + * (ZONE_DEVICE page have an elevated refcount of 1 as default so + * that they are not release to the general page allocator). + * + * Note that callback has exclusive ownership of the page (as no + * one is holding any reference). + */ + void (*free)(struct hmm_devmem *devmem, struct page *page); + /* + * fault() - CPU page fault or get user page (GUP) + * @devmem: device memory structure (see struct hmm_devmem) + * @vma: virtual memory area containing the virtual address + * @addr: virtual address that faulted or for which there is a GUP + * @page: pointer to struct page backing virtual address (unreliable) + * @flags: FAULT_FLAG_* (see include/linux/mm.h) + * @pmdp: page middle directory + * Returns: VM_FAULT_MINOR/MAJOR on success or one of VM_FAULT_ERROR + * on error + * + * The callback occurs whenever there is a CPU page fault or GUP on a + * virtual address. This means that the device driver must migrate the + * page back to regular memory (CPU accessible). + * + * The device driver is free to migrate more than one page from the + * fault() callback as an optimization. However if device decide to + * migrate more than one page it must always priotirize the faulting + * address over the others. + * + * The struct page pointer is only given as an hint to allow quick + * lookup of internal device driver data. A concurrent migration + * might have already free that page and the virtual address might + * not longer be back by it. So it should not be modified by the + * callback. + * + * Note that mmap semaphore is held in read mode at least when this + * callback occurs, hence the vma is valid upon callback entry. + */ + int (*fault)(struct hmm_devmem *devmem, + struct vm_area_struct *vma, + unsigned long addr, + const struct page *page, + unsigned int flags, + pmd_t *pmdp); +}; + +/* + * struct hmm_devmem - track device memory + * + * @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) +{ + unsigned long *drvdata = (unsigned long *)&page->pgmap; + + drvdata[1] = 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(struct page *page) +{ + unsigned long *drvdata = (unsigned long *)&page->pgmap; + + return drvdata[1]; +} + + +/* + * 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 */ +#endif /* IS_ENABLED(CONFIG_HMM) */ + +/* Below are for HMM internal use only! Not to be used by device driver! */ +#if IS_ENABLED(CONFIG_HMM_MIRROR) +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_MIRROR) */ +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_MIRROR) */ + + +#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 /* LINUX_HMM_H */ |