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/* SPDX-License-Identifier: GPL-2.0-or-later / / * Copyright 2013 Red Hat Inc. * * Authors: Jérôme Glisse <jglisse@redhat.com> / / * Heterogeneous Memory Management (HMM) * * See Documentation/vm/hmm.rst 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 a range of the CPU * page tables 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> #include <asm/pgtable.h> #ifdef CONFIG_HMM_MIRROR #include <linux/device.h> #include <linux/migrate.h> #include <linux/memremap.h> #include <linux/completion.h> #include <linux/mmu_notifier.h> / * struct hmm - HMM per mm struct * * @mm: mm struct this HMM struct is bound to * @lock: lock protecting ranges list * @ranges: list of range being snapshotted * @mirrors: list of mirrors for this mm * @mmu_notifier: mmu notifier to track updates to CPU page table * @mirrors_sem: read/write semaphore protecting the mirrors list * @wq: wait queue for user waiting on a range invalidation * @notifiers: count of active mmu notifiers / struct hmm { struct mmu_notifier mmu_notifier; spinlock_t ranges_lock; struct list_head ranges; struct list_head mirrors; struct rw_semaphore mirrors_sem; wait_queue_head_t wq; long notifiers; }; / * hmm_pfn_flag_e - HMM flag enums * * Flags: * HMM_PFN_VALID: pfn is valid. It has, at least, read permission. * HMM_PFN_WRITE: CPU page table has write permission set * HMM_PFN_DEVICE_PRIVATE: private device memory (ZONE_DEVICE) * * The driver provides a flags array for mapping page protections to device * PTE bits. If the driver valid bit for an entry is bit 3, * i.e., (entry & (1 << 3)), then the driver must provide * an array in hmm_range.flags with hmm_range.flags[HMM_PFN_VALID] == 1 << 3. * Same logic apply to all flags. This is the same idea as vm_page_prot in vma * except that this is per device driver rather than per architecture. / enum hmm_pfn_flag_e { HMM_PFN_VALID = 0, HMM_PFN_WRITE, HMM_PFN_DEVICE_PRIVATE, HMM_PFN_FLAG_MAX }; / * hmm_pfn_value_e - HMM pfn special value * * Flags: * HMM_PFN_ERROR: corresponding CPU page table entry points to poisoned memory * HMM_PFN_NONE: corresponding CPU page table entry is pte_none() * HMM_PFN_SPECIAL: corresponding CPU page table entry is special; i.e., the * result of vmf_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. * * Driver provides values for none entry, error entry, and special entry. * Driver can alias (i.e., use same value) error and special, but * it should not alias none with error or special. * * HMM pfn value returned by hmm_vma_get_pfns() or hmm_vma_fault() will be: * hmm_range.values[HMM_PFN_ERROR] if CPU page table entry is poisonous, * hmm_range.values[HMM_PFN_NONE] if there is no CPU page table entry, * hmm_range.values[HMM_PFN_SPECIAL] if CPU page table entry is a special one / enum hmm_pfn_value_e { HMM_PFN_ERROR, HMM_PFN_NONE, HMM_PFN_SPECIAL, HMM_PFN_VALUE_MAX }; / * struct hmm_range - track invalidation lock on virtual address range * * @hmm: the core HMM structure this range is active against * @vma: the vm area struct for the 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) * @flags: pfn flags to match device driver page table * @values: pfn value for some special case (none, special, error, ...) * @default_flags: default flags for the range (write, read, ... see hmm doc) * @pfn_flags_mask: allows to mask pfn flags so that only default_flags matter * @pfn_shifts: pfn shift value (should be <= PAGE_SHIFT) * @valid: pfns array did not change since it has been fill by an HMM function / struct hmm_range { struct hmm hmm; struct list_head list; unsigned long start; unsigned long end; uint64_t pfns; const uint64_t flags; const uint64_t values; uint64_t default_flags; uint64_t pfn_flags_mask; uint8_t pfn_shift; bool valid; }; / * hmm_range_wait_until_valid() - wait for range to be valid * @range: range affected by invalidation to wait on * @timeout: time out for wait in ms (ie abort wait after that period of time) * Return: true if the range is valid, false otherwise. / static inline bool hmm_range_wait_until_valid(struct hmm_range range, unsigned long timeout) { return wait_event_timeout(range->hmm->wq, range->valid, msecs_to_jiffies(timeout)) != 0; } /* * hmm_range_valid() - test if a range is valid or not * @range: range * Return: true if the range is valid, false otherwise. / static inline bool hmm_range_valid(struct hmm_range range) { return range->valid; } /* * hmm_device_entry_to_page() - return struct page pointed to by a device entry * @range: range use to decode device entry value * @entry: device entry value to get corresponding struct page from * Return: struct page pointer if entry is a valid, NULL otherwise * * If the device entry is valid (ie valid flag set) then return the struct page * matching the entry value. Otherwise return NULL. / static inline struct page hmm_device_entry_to_page(const struct hmm_range range, uint64_t entry) { if (entry == range->values[HMM_PFN_NONE]) return NULL; if (entry == range->values[HMM_PFN_ERROR]) return NULL; if (entry == range->values[HMM_PFN_SPECIAL]) return NULL; if (!(entry & range->flags[HMM_PFN_VALID])) return NULL; return pfn_to_page(entry >> range->pfn_shift); } / * hmm_device_entry_to_pfn() - return pfn value store in a device entry * @range: range use to decode device entry value * @entry: device entry to extract pfn from * Return: pfn value if device entry is valid, -1UL otherwise / static inline unsigned long hmm_device_entry_to_pfn(const struct hmm_range range, uint64_t pfn) { if (pfn == range->values[HMM_PFN_NONE]) return -1UL; if (pfn == range->values[HMM_PFN_ERROR]) return -1UL; if (pfn == range->values[HMM_PFN_SPECIAL]) return -1UL; if (!(pfn & range->flags[HMM_PFN_VALID])) return -1UL; return (pfn >> range->pfn_shift); } /* * hmm_device_entry_from_page() - create a valid device entry for a page * @range: range use to encode HMM pfn value * @page: page for which to create the device entry * Return: valid device entry for the page / static inline uint64_t hmm_device_entry_from_page(const struct hmm_range range, struct page page) { return (page_to_pfn(page) << range->pfn_shift) \| range->flags[HMM_PFN_VALID]; } / * hmm_device_entry_from_pfn() - create a valid device entry value from pfn * @range: range use to encode HMM pfn value * @pfn: pfn value for which to create the device entry * Return: valid device entry for the pfn / static inline uint64_t hmm_device_entry_from_pfn(const struct hmm_range range, unsigned long pfn) { return (pfn << range->pfn_shift) \| range->flags[HMM_PFN_VALID]; } /* * 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; / * struct hmm_mirror_ops - HMM mirror device operations callback * * @update: callback to update range on a device / struct hmm_mirror_ops { / release() - release hmm_mirror * * @mirror: pointer to struct hmm_mirror * * This is called when the mm_struct is being released. The callback * must ensure that all access to any pages obtained from this mirror * is halted before the callback returns. All future access should * fault. / void (release)(struct hmm_mirror mirror); / sync_cpu_device_pagetables() - synchronize page tables * * @mirror: pointer to struct hmm_mirror * @update: update information (see struct mmu_notifier_range) * Return: -EAGAIN if mmu_notifier_range_blockable(update) is false * and callback needs to block, 0 otherwise. * * 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. / int (sync_cpu_device_pagetables)( struct hmm_mirror mirror, const struct mmu_notifier_range update); }; /* * 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); /* * Please see Documentation/vm/hmm.rst for how to use the range API. / int hmm_range_register(struct hmm_range range, struct hmm_mirror mirror); void hmm_range_unregister(struct hmm_range range); /* * Retry fault if non-blocking, drop mmap_sem and return -EAGAIN in that case. / #define HMM_FAULT_ALLOW_RETRY (1 << 0) / Don't fault in missing PTEs, just snapshot the current state. / #define HMM_FAULT_SNAPSHOT (1 << 1) long hmm_range_fault(struct hmm_range range, unsigned int flags); long hmm_range_dma_map(struct hmm_range range, struct device device, dma_addr_t daddrs, unsigned int flags); long hmm_range_dma_unmap(struct hmm_range range, struct device device, dma_addr_t daddrs, bool dirty); /* * HMM_RANGE_DEFAULT_TIMEOUT - default timeout (ms) when waiting for a range * * When waiting for mmu notifiers we need some kind of time out otherwise we * could potentialy wait for ever, 1000ms ie 1s sounds like a long time to * wait already. / #define HMM_RANGE_DEFAULT_TIMEOUT 1000 #endif / IS_ENABLED(CONFIG_HMM_MIRROR) / #endif / LINUX_HMM_H */

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