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-rw-r--r--include/linux/hmm.h110
-rw-r--r--mm/Kconfig12
-rw-r--r--mm/hmm.c153
3 files changed, 260 insertions, 15 deletions
diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index 5d83fec6dfdd..76310726ee9c 100644
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h
@@ -72,6 +72,7 @@
#if IS_ENABLED(CONFIG_HMM)
+struct hmm;
/*
* hmm_pfn_t - HMM uses its own pfn type to keep several flags per page
@@ -134,6 +135,115 @@ static inline hmm_pfn_t hmm_pfn_t_from_pfn(unsigned long 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_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 {
+ /* 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);
+#endif /* IS_ENABLED(CONFIG_HMM_MIRROR) */
+
+
/* Below are for HMM internal use only! Not to be used by device driver! */
void hmm_mm_destroy(struct mm_struct *mm);
diff --git a/mm/Kconfig b/mm/Kconfig
index 037fa26d16a2..254db99f263d 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -705,6 +705,18 @@ config ARCH_HAS_HMM
config HMM
bool
+config HMM_MIRROR
+ bool "HMM mirror CPU page table into a device page table"
+ depends on ARCH_HAS_HMM
+ select MMU_NOTIFIER
+ select HMM
+ help
+ Select HMM_MIRROR 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.
+
config FRAME_VECTOR
bool
diff --git a/mm/hmm.c b/mm/hmm.c
index de032ff9e576..d37daf9edcd3 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -21,16 +21,27 @@
#include <linux/hmm.h>
#include <linux/slab.h>
#include <linux/sched.h>
+#include <linux/mmu_notifier.h>
#ifdef CONFIG_HMM
+static const struct mmu_notifier_ops hmm_mmu_notifier_ops;
+
/*
* struct hmm - HMM per mm struct
*
* @mm: mm struct this HMM struct is bound to
+ * @sequence: we track updates to the CPU page table with a sequence number
+ * @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
*/
struct hmm {
struct mm_struct *mm;
+ atomic_t sequence;
+ struct list_head mirrors;
+ struct mmu_notifier mmu_notifier;
+ struct rw_semaphore mirrors_sem;
};
/*
@@ -43,27 +54,48 @@ struct hmm {
*/
static struct hmm *hmm_register(struct mm_struct *mm)
{
- if (!mm->hmm) {
- struct hmm *hmm = NULL;
-
- hmm = kmalloc(sizeof(*hmm), GFP_KERNEL);
- if (!hmm)
- return NULL;
- hmm->mm = mm;
-
- spin_lock(&mm->page_table_lock);
- if (!mm->hmm)
- mm->hmm = hmm;
- else
- kfree(hmm);
- spin_unlock(&mm->page_table_lock);
- }
+ struct hmm *hmm = READ_ONCE(mm->hmm);
+ bool cleanup = false;
/*
* The hmm struct can only be freed once the mm_struct goes away,
* hence we should always have pre-allocated an new hmm struct
* above.
*/
+ if (hmm)
+ return hmm;
+
+ hmm = kmalloc(sizeof(*hmm), GFP_KERNEL);
+ if (!hmm)
+ return NULL;
+ INIT_LIST_HEAD(&hmm->mirrors);
+ init_rwsem(&hmm->mirrors_sem);
+ atomic_set(&hmm->sequence, 0);
+ hmm->mmu_notifier.ops = NULL;
+ hmm->mm = mm;
+
+ /*
+ * We should only get here if hold the mmap_sem in write mode ie on
+ * registration of first mirror through hmm_mirror_register()
+ */
+ hmm->mmu_notifier.ops = &hmm_mmu_notifier_ops;
+ if (__mmu_notifier_register(&hmm->mmu_notifier, mm)) {
+ kfree(hmm);
+ return NULL;
+ }
+
+ spin_lock(&mm->page_table_lock);
+ if (!mm->hmm)
+ mm->hmm = hmm;
+ else
+ cleanup = true;
+ spin_unlock(&mm->page_table_lock);
+
+ if (cleanup) {
+ mmu_notifier_unregister(&hmm->mmu_notifier, mm);
+ kfree(hmm);
+ }
+
return mm->hmm;
}
@@ -72,3 +104,94 @@ void hmm_mm_destroy(struct mm_struct *mm)
kfree(mm->hmm);
}
#endif /* CONFIG_HMM */
+
+#if IS_ENABLED(CONFIG_HMM_MIRROR)
+static void hmm_invalidate_range(struct hmm *hmm,
+ enum hmm_update_type action,
+ unsigned long start,
+ unsigned long end)
+{
+ struct hmm_mirror *mirror;
+
+ down_read(&hmm->mirrors_sem);
+ list_for_each_entry(mirror, &hmm->mirrors, list)
+ mirror->ops->sync_cpu_device_pagetables(mirror, action,
+ start, end);
+ up_read(&hmm->mirrors_sem);
+}
+
+static void hmm_invalidate_range_start(struct mmu_notifier *mn,
+ struct mm_struct *mm,
+ unsigned long start,
+ unsigned long end)
+{
+ struct hmm *hmm = mm->hmm;
+
+ VM_BUG_ON(!hmm);
+
+ atomic_inc(&hmm->sequence);
+}
+
+static void hmm_invalidate_range_end(struct mmu_notifier *mn,
+ struct mm_struct *mm,
+ unsigned long start,
+ unsigned long end)
+{
+ struct hmm *hmm = mm->hmm;
+
+ VM_BUG_ON(!hmm);
+
+ hmm_invalidate_range(mm->hmm, HMM_UPDATE_INVALIDATE, start, end);
+}
+
+static const struct mmu_notifier_ops hmm_mmu_notifier_ops = {
+ .invalidate_range_start = hmm_invalidate_range_start,
+ .invalidate_range_end = hmm_invalidate_range_end,
+};
+
+/*
+ * hmm_mirror_register() - register a mirror against an mm
+ *
+ * @mirror: new mirror struct to register
+ * @mm: mm to register against
+ *
+ * To start mirroring a process address space, the device driver must register
+ * an HMM mirror struct.
+ *
+ * THE mm->mmap_sem MUST BE HELD IN WRITE MODE !
+ */
+int hmm_mirror_register(struct hmm_mirror *mirror, struct mm_struct *mm)
+{
+ /* Sanity check */
+ if (!mm || !mirror || !mirror->ops)
+ return -EINVAL;
+
+ mirror->hmm = hmm_register(mm);
+ if (!mirror->hmm)
+ return -ENOMEM;
+
+ down_write(&mirror->hmm->mirrors_sem);
+ list_add(&mirror->list, &mirror->hmm->mirrors);
+ up_write(&mirror->hmm->mirrors_sem);
+
+ return 0;
+}
+EXPORT_SYMBOL(hmm_mirror_register);
+
+/*
+ * hmm_mirror_unregister() - unregister a mirror
+ *
+ * @mirror: new mirror struct to register
+ *
+ * Stop mirroring a process address space, and cleanup.
+ */
+void hmm_mirror_unregister(struct hmm_mirror *mirror)
+{
+ struct hmm *hmm = mirror->hmm;
+
+ down_write(&hmm->mirrors_sem);
+ list_del(&mirror->list);
+ up_write(&hmm->mirrors_sem);
+}
+EXPORT_SYMBOL(hmm_mirror_unregister);
+#endif /* IS_ENABLED(CONFIG_HMM_MIRROR) */