/* 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 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 #include #include #include #include #include #include /* * 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 * * @notifier: a mmu_interval_notifier that includes the start/end * @notifier_seq: result of mmu_interval_read_begin() * @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 mmu_interval_notifier *notifier; unsigned long notifier_seq; 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; }; /* * 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]; } /* * 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) #ifdef CONFIG_HMM_MIRROR /* * Please see Documentation/vm/hmm.rst for how to use the range API. */ long hmm_range_fault(struct hmm_range *range, unsigned int flags); #else static inline long hmm_range_fault(struct hmm_range *range, unsigned int flags) { return -EOPNOTSUPP; } #endif /* * 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 /* LINUX_HMM_H */