/* SPDX-License-Identifier: GPL-2.0-or-later */ /* * Copyright 2013 Red Hat Inc. * * Authors: Jérôme Glisse */ /* * 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 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 #include #if IS_ENABLED(CONFIG_HMM) #include #include #include #include #include /* * 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 * @dead: is the mm dead ? */ struct hmm { struct mm_struct *mm; struct kref kref; struct mutex lock; struct list_head ranges; struct list_head mirrors; struct mmu_notifier mmu_notifier; struct rw_semaphore mirrors_sem; wait_queue_head_t wq; long notifiers; bool dead; }; /* * 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 provide a flags array, if driver valid bit for an entry is bit * 3 ie (entry & (1 << 3)) is true if entry is valid then 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 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 provide entry value for none entry, error entry and special entry, * driver can alias (ie use same value for error and special for instance). It * should not alias none and 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 * 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 vm_area_struct *vma; 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 page_shift; uint8_t pfn_shift; bool valid; }; /* * hmm_range_page_shift() - return the page shift for the range * @range: range being queried * Returns: page shift (page size = 1 << page shift) for the range */ static inline unsigned hmm_range_page_shift(const struct hmm_range *range) { return range->page_shift; } /* * hmm_range_page_size() - return the page size for the range * @range: range being queried * Returns: page size for the range in bytes */ static inline unsigned long hmm_range_page_size(const struct hmm_range *range) { return 1UL << hmm_range_page_shift(range); } /* * 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) * Returns: true if the range is valid, false otherwise. */ static inline bool hmm_range_wait_until_valid(struct hmm_range *range, unsigned long timeout) { /* Check if mm is dead ? */ if (range->hmm == NULL || range->hmm->dead || range->hmm->mm == NULL) { range->valid = false; return false; } if (range->valid) return true; wait_event_timeout(range->hmm->wq, range->valid || range->hmm->dead, msecs_to_jiffies(timeout)); /* Return current valid status just in case we get lucky */ return range->valid; } /* * hmm_range_valid() - test if a range is valid or not * @range: range * Returns: 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 * Returns: 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 * Returns: 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 * Returns: 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 * Returns: 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]; } /* * Old API: * hmm_pfn_to_page() * hmm_pfn_to_pfn() * hmm_pfn_from_page() * hmm_pfn_from_pfn() * * This are the OLD API please use new API, it is here to avoid cross-tree * merge painfullness ie we convert things to new API in stages. */ static inline struct page *hmm_pfn_to_page(const struct hmm_range *range, uint64_t pfn) { return hmm_device_entry_to_page(range, pfn); } static inline unsigned long hmm_pfn_to_pfn(const struct hmm_range *range, uint64_t pfn) { return hmm_device_entry_to_pfn(range, pfn); } static inline uint64_t hmm_pfn_from_page(const struct hmm_range *range, struct page *page) { return hmm_device_entry_from_page(range, page); } static inline uint64_t hmm_pfn_from_pfn(const struct hmm_range *range, unsigned long pfn) { return hmm_device_entry_from_pfn(range, pfn); } #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_event - type of update * @HMM_UPDATE_INVALIDATE: invalidate range (no indication as to why) */ enum hmm_update_event { HMM_UPDATE_INVALIDATE, }; /* * struct hmm_update - HMM update informations for callback * * @start: virtual start address of the range to update * @end: virtual end address of the range to update * @event: event triggering the update (what is happening) * @blockable: can the callback block/sleep ? */ struct hmm_update { unsigned long start; unsigned long end; enum hmm_update_event event; bool blockable; }; /* * 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 should make sure no references to the mirror occur * after the callback returns. */ void (*release)(struct hmm_mirror *mirror); /* sync_cpu_device_pagetables() - synchronize page tables * * @mirror: pointer to struct hmm_mirror * @update: update informations (see struct hmm_update) * Returns: -EAGAIN if update.blockable false and callback need 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 hmm_update *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); /* * hmm_mirror_mm_is_alive() - test if mm is still alive * @mirror: the HMM mm mirror for which we want to lock the mmap_sem * Returns: false if the mm is dead, true otherwise * * This is an optimization it will not accurately always return -EINVAL if the * mm is dead ie there can be false negative (process is being kill but HMM is * not yet inform of that). It is only intented to be use to optimize out case * where driver is about to do something time consuming and it would be better * to skip it if the mm is dead. */ static inline bool hmm_mirror_mm_is_alive(struct hmm_mirror *mirror) { struct mm_struct *mm; if (!mirror || !mirror->hmm) return false; mm = READ_ONCE(mirror->hmm->mm); if (mirror->hmm->dead || !mm) return false; return true; } /* * Please see Documentation/vm/hmm.rst for how to use the range API. */ int hmm_range_register(struct hmm_range *range, struct mm_struct *mm, unsigned long start, unsigned long end, unsigned page_shift); void hmm_range_unregister(struct hmm_range *range); long hmm_range_snapshot(struct hmm_range *range); long hmm_range_fault(struct hmm_range *range, bool block); long hmm_range_dma_map(struct hmm_range *range, struct device *device, dma_addr_t *daddrs, bool block); long hmm_range_dma_unmap(struct hmm_range *range, struct vm_area_struct *vma, 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 /* This is a temporary helper to avoid merge conflict between trees. */ static inline bool hmm_vma_range_done(struct hmm_range *range) { bool ret = hmm_range_valid(range); hmm_range_unregister(range); return ret; } /* This is a temporary helper to avoid merge conflict between trees. */ static inline int hmm_vma_fault(struct hmm_range *range, bool block) { long ret; /* * With the old API the driver must set each individual entries with * the requested flags (valid, write, ...). So here we set the mask to * keep intact the entries provided by the driver and zero out the * default_flags. */ range->default_flags = 0; range->pfn_flags_mask = -1UL; ret = hmm_range_register(range, range->vma->vm_mm, range->start, range->end, PAGE_SHIFT); if (ret) return (int)ret; if (!hmm_range_wait_until_valid(range, HMM_RANGE_DEFAULT_TIMEOUT)) { /* * The mmap_sem was taken by driver we release it here and * returns -EAGAIN which correspond to mmap_sem have been * drop in the old API. */ up_read(&range->vma->vm_mm->mmap_sem); return -EAGAIN; } ret = hmm_range_fault(range, block); if (ret <= 0) { if (ret == -EBUSY || !ret) { /* Same as above drop mmap_sem to match old API. */ up_read(&range->vma->vm_mm->mmap_sem); ret = -EBUSY; } else if (ret == -EAGAIN) ret = -EBUSY; hmm_range_unregister(range); return ret; } return 0; } /* 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_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) */ #if IS_ENABLED(CONFIG_DEVICE_PRIVATE) 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. */ vm_fault_t (*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 * @page_fault: callback when CPU fault on an unaddressable device page * * 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. * * The page_fault() callback must migrate page back, from device memory to * system memory, so that the CPU can access it. This might fail for various * reasons (device issues, device have been unplugged, ...). When such error * conditions happen, the page_fault() callback must return VM_FAULT_SIGBUS and * set the CPU page table entry to "poisoned". * * Note that because memory cgroup charges are transferred to the device memory, * this should never fail due to memory restrictions. However, allocation * of a regular system page might still fail because we are out of memory. If * that happens, the page_fault() callback must return VM_FAULT_OOM. * * The page_fault() callback can also try to migrate back multiple pages in one * chunk, as an optimization. It must, however, prioritize the faulting address * over all the others. */ typedef vm_fault_t (*dev_page_fault_t)(struct vm_area_struct *vma, unsigned long addr, const struct page *page, unsigned int flags, pmd_t *pmdp); 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; dev_page_fault_t page_fault; }; /* * 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. */ struct hmm_devmem *hmm_devmem_add(const struct hmm_devmem_ops *ops, struct device *device, unsigned long size); /* * 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) { page->hmm_data = 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(const struct page *page) { return page->hmm_data; } #endif /* CONFIG_DEVICE_PRIVATE */ #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 /* IS_ENABLED(CONFIG_HMM) */ #endif /* LINUX_HMM_H */