/* * 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) #include #include #include #include struct hmm; /* * 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_ERROR: corresponding CPU page table entry points to poisoned memory * 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_PRIVATE: unaddressable device memory (ZONE_DEVICE) */ #define HMM_PFN_VALID (1 << 0) #define HMM_PFN_WRITE (1 << 1) #define HMM_PFN_ERROR (1 << 2) #define HMM_PFN_SPECIAL (1 << 3) #define HMM_PFN_DEVICE_PRIVATE (1 << 4) #define HMM_PFN_SHIFT 5 /* * hmm_pfn_to_page() - return struct page pointed to by a valid HMM pfn * @pfn: HMM pfn value to get corresponding struct page from * Returns: struct page pointer if pfn is a valid HMM pfn, NULL otherwise * * If the HMM pfn is valid (ie valid flag set) then return the struct page * matching the pfn value stored in the HMM pfn. Otherwise return NULL. */ static inline struct page *hmm_pfn_to_page(uint64_t pfn) { if (!(pfn & HMM_PFN_VALID)) return NULL; return pfn_to_page(pfn >> HMM_PFN_SHIFT); } /* * hmm_pfn_to_pfn() - return pfn value store in a HMM pfn * @pfn: HMM pfn value to extract pfn from * Returns: pfn value if HMM pfn is valid, -1UL otherwise */ static inline unsigned long hmm_pfn_to_pfn(uint64_t pfn) { if (!(pfn & HMM_PFN_VALID)) return -1UL; return (pfn >> HMM_PFN_SHIFT); } /* * hmm_pfn_from_page() - create a valid HMM pfn value from struct page * @page: struct page pointer for which to create the HMM pfn * Returns: valid HMM pfn for the page */ static inline uint64_t hmm_pfn_from_page(struct page *page) { return (page_to_pfn(page) << HMM_PFN_SHIFT) | HMM_PFN_VALID; } /* * hmm_pfn_from_pfn() - create a valid HMM pfn value from pfn * @pfn: pfn value for which to create the HMM pfn * Returns: valid HMM pfn for the pfn */ static inline uint64_t hmm_pfn_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 { /* 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_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 * * @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) * @valid: pfns array did not change since it has been fill by an HMM function */ struct hmm_range { struct vm_area_struct *vma; struct list_head list; unsigned long start; unsigned long end; uint64_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 hmm_range *range); bool hmm_vma_range_done(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 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 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 hmm_range *range, 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(const struct page *page) { const unsigned long *drvdata = (const 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 */ /* 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) */ 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 */