/*
* 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.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>
#if IS_ENABLED(CONFIG_HMM)
#include <linux/device.h>
#include <linux/migrate.h>
#include <linux/memremap.h>
#include <linux/completion.h>
#include <linux/mmu_notifier.h>
/*
* We need this because from rhel 8.0 to rhel 8.1 this struct definition was
* hidden in a C file. Now we need to expose it in this header file and thus
* to silence KABI check we need to gard it with GENKSYMS this is ok because
* HMM is never going to be a whitelist KABI as it would impede other back-
* port.
*/
#ifndef __GENKSYMS__
/*
* 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 mm_struct *mm;
struct kref kref;
spinlock_t ranges_lock;
struct list_head ranges;
struct list_head mirrors;
struct mmu_notifier mmu_notifier;
struct rw_semaphore mirrors_sem;
wait_queue_head_t wq;
struct rcu_head rcu;
long notifiers;
};
#endif
/*
* 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 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.
*
* 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
* @page_shift: device virtual address shift value (should be >= PAGE_SHIFT)
* @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
* Return: 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
* Return: 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)
* 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];
}
/*
* 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 information 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 information (see struct hmm_update)
* Return: -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);
/*
* 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,
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
/* Below are for HMM internal use only! Not to be used by device driver! */
static inline void hmm_mm_init(struct mm_struct *mm)
{
mm->hmm = NULL;
}
#else /* IS_ENABLED(CONFIG_HMM_MIRROR) */
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
* Return: 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 the device decides
* to migrate more than one page it must always priotirize the faulting
* address over the others.
*
* The struct page pointer is only given as a hint to allow quick
* lookup of internal device driver data. A concurrent migration
* might have already freed that page and the virtual address might
* no longer be backed 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 is a 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.
*/
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.
*/
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 */