[HMM 10/16] mm/hmm/mirror: helper to snapshot CPU page table v2

Jérôme Glisse
2017-04-05T20:43:38Z

This does not use existing page table walker because we want to share
same code for our page fault handler.

Changes since v1:
- Use spinlock instead of rcu synchronized list traversal

Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
Signed-off-by: Evgeny Baskakov <ebaskakov@nvidia.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Mark Hairgrove <mhairgrove@nvidia.com>
Signed-off-by: Sherry Cheung <SCheung@nvidia.com>
Signed-off-by: Subhash Gutti <sgutti@nvidia.com>
---
include/linux/hmm.h | 55 +++++++++-
mm/hmm.c | 285 ++++++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 338 insertions(+), 2 deletions(-)

diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index 6668a1b..defa7cd 100644
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h
@@ -79,13 +79,26 @@ struct hmm;
*
* Flags:
* HMM_PFN_VALID: pfn is valid
+ * HMM_PFN_READ: CPU page table has read permission set
* HMM_PFN_WRITE: CPU page table has write permission set
+ * HMM_PFN_ERROR: corresponding CPU page table entry points to poisoned memory
+ * HMM_PFN_EMPTY: 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.
+ * HMM_PFN_DEVICE_UNADDRESSABLE: unaddressable device memory (ZONE_DEVICE)
*/
typedef unsigned long hmm_pfn_t;

#define HMM_PFN_VALID (1 << 0)
-#define HMM_PFN_WRITE (1 << 1)
-#define HMM_PFN_SHIFT 2
+#define HMM_PFN_READ (1 << 1)
+#define HMM_PFN_WRITE (1 << 2)
+#define HMM_PFN_ERROR (1 << 3)
+#define HMM_PFN_EMPTY (1 << 4)
+#define HMM_PFN_SPECIAL (1 << 5)
+#define HMM_PFN_DEVICE_UNADDRESSABLE (1 << 6)
+#define HMM_PFN_SHIFT 7

/*
* hmm_pfn_t_to_page() - return struct page pointed to by a valid hmm_pfn_t
@@ -241,6 +254,44 @@ struct hmm_mirror {

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
+ *
+ * @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 list_head list;
+ unsigned long start;
+ unsigned long end;
+ hmm_pfn_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 vm_area_struct *vma,
+ struct hmm_range *range,
+ unsigned long start,
+ unsigned long end,
+ hmm_pfn_t *pfns);
+bool hmm_vma_range_done(struct vm_area_struct *vma, struct hmm_range *range);
#endif /* IS_ENABLED(CONFIG_HMM_MIRROR) */

diff --git a/mm/hmm.c b/mm/hmm.c
index 7ed4b4c..4828b97 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -19,8 +19,12 @@
*/
#include <linux/mm.h>
#include <linux/hmm.h>
+#include <linux/rmap.h>
+#include <linux/swap.h>
#include <linux/slab.h>
#include <linux/sched.h>
+#include <linux/swapops.h>
+#include <linux/hugetlb.h>
#include <linux/mmu_notifier.h>

static const struct mmu_notifier_ops hmm_mmu_notifier_ops;
@@ -30,14 +34,18 @@ 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
+ * @lock: lock protecting ranges list
* @sequence: we track updates to the CPU page table with a sequence number
+ * @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
*/
struct hmm {
struct mm_struct *mm;
+ spinlock_t lock;
atomic_t sequence;
+ struct list_head ranges;
struct list_head mirrors;
struct mmu_notifier mmu_notifier;
struct rw_semaphore mirrors_sem;
@@ -71,6 +79,8 @@ static struct hmm *hmm_register(struct mm_struct *mm)
init_rwsem(&hmm->mirrors_sem);
atomic_set(&hmm->sequence, 0);
hmm->mmu_notifier.ops = NULL;
+ INIT_LIST_HEAD(&hmm->ranges);
+ spin_lock_init(&hmm->lock);
hmm->mm = mm;

/*
@@ -111,6 +121,22 @@ static void hmm_invalidate_range(struct hmm *hmm,
unsigned long end)
{
struct hmm_mirror *mirror;
+ struct hmm_range *range;
+
+ spin_lock(&hmm->lock);
+ list_for_each_entry(range, &hmm->ranges, list) {
+ unsigned long addr, idx, npages;
+
+ if (end < range->start || start >= range->end)
+ continue;
+
+ range->valid = false;
+ addr = max(start, range->start);
+ idx = (addr - range->start) >> PAGE_SHIFT;
+ npages = (min(range->end, end) - addr) >> PAGE_SHIFT;
+ memset(&range->pfns[idx], 0, sizeof(*range->pfns) * npages);
+ }
+ spin_unlock(&hmm->lock);

down_read(&hmm->mirrors_sem);
list_for_each_entry(mirror, &hmm->mirrors, list)
@@ -208,4 +234,263 @@ void hmm_mirror_unregister(struct hmm_mirror *mirror)
up_write(&hmm->mirrors_sem);
}
EXPORT_SYMBOL(hmm_mirror_unregister);
+
+static void hmm_pfns_special(hmm_pfn_t *pfns,
+ unsigned long addr,
+ unsigned long end)
+{
+ for (; addr < end; addr += PAGE_SIZE, pfns++)
+ *pfns = HMM_PFN_SPECIAL;
+}
+
+static int hmm_vma_walk_hole(unsigned long addr,
+ unsigned long end,
+ struct mm_walk *walk)
+{
+ struct hmm_range *range = walk->private;
+ hmm_pfn_t *pfns = range->pfns;
+ unsigned long i;
+
+ i = (addr - range->start) >> PAGE_SHIFT;
+ for (; addr < end; addr += PAGE_SIZE, i++)
+ pfns[i] = HMM_PFN_EMPTY;
+
+ return 0;
+}
+
+static int hmm_vma_walk_clear(unsigned long addr,
+ unsigned long end,
+ struct mm_walk *walk)
+{
+ struct hmm_range *range = walk->private;
+ hmm_pfn_t *pfns = range->pfns;
+ unsigned long i;
+
+ i = (addr - range->start) >> PAGE_SHIFT;
+ for (; addr < end; addr += PAGE_SIZE, i++)
+ pfns[i] = 0;
+
+ return 0;
+}
+
+static int hmm_vma_walk_pmd(pmd_t *pmdp,
+ unsigned long start,
+ unsigned long end,
+ struct mm_walk *walk)
+{
+ struct hmm_range *range = walk->private;
+ struct vm_area_struct *vma = walk->vma;
+ hmm_pfn_t *pfns = range->pfns;
+ unsigned long addr = start, i;
+ hmm_pfn_t flag;
+ pte_t *ptep;
+
+ i = (addr - range->start) >> PAGE_SHIFT;
+ flag = vma->vm_flags & VM_READ ? HMM_PFN_READ : 0;
+
+ if (pmd_none(*pmdp) || pmd_trans_unstable(pmdp)) {
+ pmd_t pmd;
+
+ pmd = pmd_read_atomic(pmdp);
+ barrier();
+ if (pmd_none(pmd))
+ return hmm_vma_walk_hole(start, end, walk);
+
+ if (pmd_bad(pmd) || pmd_protnone(pmd))
+ return hmm_vma_walk_clear(start, end, walk);
+
+ if (pmd_trans_huge(pmd) || pmd_devmap(pmd)) {
+ unsigned long pfn = pmd_pfn(pmd) + pte_index(addr);
+
+ flag |= pmd_write(pmd) ? HMM_PFN_WRITE : 0;
+ for (; addr < end; addr += PAGE_SIZE, i++, pfn++)
+ pfns[i] = hmm_pfn_t_from_pfn(pfn) | flag;
+ return 0;
+ } else {
+ /*
+ * Something unusual is going on. Better to have the
+ * driver assume there is nothing for this range and
+ * let the fault code path sort out proper pages for the
+ * range.
+ */
+ return hmm_vma_walk_clear(start, end, walk);
+ }
+ }
+
+ ptep = pte_offset_map(pmdp, addr);
+ for (; addr < end; addr += PAGE_SIZE, ptep++, i++) {
+ pte_t pte = *ptep;
+
+ pfns[i] = 0;
+
+ if (pte_none(pte)) {
+ pfns[i] = HMM_PFN_EMPTY;
+ continue;
+ }
+
+ if (!pte_present(pte)) {
+ swp_entry_t entry;
+
+ if (!non_swap_entry(entry))
+ continue;
+ entry = pte_to_swp_entry(pte);
+
+ /*
+ * This is a special swap entry, ignore migration, use
+ * device and report anything else as error.
+ */
+ if (is_device_entry(entry)) {
+ pfns[i] = hmm_pfn_t_from_pfn(swp_offset(entry));
+ if (is_write_device_entry(entry))
+ pfns[i] |= HMM_PFN_WRITE;
+ pfns[i] |= HMM_PFN_DEVICE_UNADDRESSABLE;
+ pfns[i] |= flag;
+ } else if (!is_migration_entry(entry)) {
+ pfns[i] = HMM_PFN_ERROR;
+ }
+ continue;
+ }
+
+ pfns[i] = hmm_pfn_t_from_pfn(pte_pfn(pte)) | flag;
+ pfns[i] |= pte_write(pte) ? HMM_PFN_WRITE : 0;
+ }
+ pte_unmap(ptep - 1);
+
+ return 0;
+}
+
+/*
+ * hmm_vma_get_pfns() - snapshot CPU page table for a range of virtual addresses
+ * @vma: virtual memory area containing the virtual address range
+ * @range: used to track snapshot validity
+ * @start: range virtual start address (inclusive)
+ * @end: range virtual end address (exclusive)
+ * @entries: array of hmm_pfn_t: provided by the caller, filled in by function
+ * Returns: -EINVAL if invalid argument, -ENOMEM out of memory, 0 success
+ *
+ * This snapshots the CPU page table for a range of virtual addresses. Snapshot
+ * validity is tracked by range struct. See hmm_vma_range_done() for further
+ * information.
+ *
+ * The range struct is initialized here. It tracks the CPU page table, but only
+ * if the function returns success (0), in which case the caller must then call
+ * hmm_vma_range_done() to stop CPU page table update tracking on this range.
+ *
+ * NOT CALLING hmm_vma_range_done() IF FUNCTION RETURNS 0 WILL LEAD TO SERIOUS
+ * MEMORY CORRUPTION ! YOU HAVE BEEN WARNED !
+ */
+int hmm_vma_get_pfns(struct vm_area_struct *vma,
+ struct hmm_range *range,
+ unsigned long start,
+ unsigned long end,
+ hmm_pfn_t *pfns)
+{
+ struct mm_walk mm_walk;
+ struct hmm *hmm;
+
+ /* FIXME support hugetlb fs */
+ if (is_vm_hugetlb_page(vma) || (vma->vm_flags & VM_SPECIAL)) {
+ hmm_pfns_special(pfns, start, end);
+ return -EINVAL;
+ }
+
+ /* Sanity check, this really should not happen ! */
+ if (start < vma->vm_start || start >= vma->vm_end)
+ return -EINVAL;
+ if (end < vma->vm_start || end > vma->vm_end)
+ return -EINVAL;
+
+ hmm = hmm_register(vma->vm_mm);
+ if (!hmm)
+ return -ENOMEM;
+ /* Caller must have registered a mirror, via hmm_mirror_register() ! */
+ if (!hmm->mmu_notifier.ops)
+ return -EINVAL;
+
+ /* Initialize range to track CPU page table update */
+ range->start = start;
+ range->pfns = pfns;
+ range->end = end;
+ spin_lock(&hmm->lock);
+ range->valid = true;
+ list_add_rcu(&range->list, &hmm->ranges);
+ spin_unlock(&hmm->lock);
+
+ mm_walk.vma = vma;
+ mm_walk.mm = vma->vm_mm;
+ mm_walk.private = range;
+ mm_walk.pte_entry = NULL;
+ mm_walk.test_walk = NULL;
+ mm_walk.hugetlb_entry = NULL;
+ mm_walk.pmd_entry = hmm_vma_walk_pmd;
+ mm_walk.pte_hole = hmm_vma_walk_hole;
+
+ walk_page_range(start, end, &mm_walk);
+
+ return 0;
+}
+EXPORT_SYMBOL(hmm_vma_get_pfns);
+
+/*
+ * hmm_vma_range_done() - stop tracking change to CPU page table over a range
+ * @vma: virtual memory area containing the virtual address range
+ * @range: range being tracked
+ * Returns: false if range data has been invalidated, true otherwise
+ *
+ * Range struct is used to track updates to the CPU page table after a call to
+ * either hmm_vma_get_pfns() or hmm_vma_fault(). Once the device driver is done
+ * using the data, or wants to lock updates to the data it got from those
+ * functions, it must call the hmm_vma_range_done() function, which will then
+ * stop tracking CPU page table updates.
+ *
+ * Note that device driver must still implement general CPU page table update
+ * tracking either by using hmm_mirror (see hmm_mirror_register()) or by using
+ * the mmu_notifier API directly.
+ *
+ * CPU page table update tracking done through hmm_range is only temporary and
+ * to be used while trying to duplicate CPU page table contents for a range of
+ * virtual addresses.
+ *
+ * There are two ways to use this :
+ * again:
+ * hmm_vma_get_pfns(vma, range, start, end, pfns);
+ * trans = device_build_page_table_update_transaction(pfns);
+ * device_page_table_lock();
+ * if (!hmm_vma_range_done(vma, range)) {
+ * device_page_table_unlock();
+ * goto again;
+ * }
+ * device_commit_transaction(trans);
+ * device_page_table_unlock();
+ *
+ * Or:
+ * hmm_vma_get_pfns(vma, range, start, end, pfns);
+ * device_page_table_lock();
+ * hmm_vma_range_done(vma, range);
+ * device_update_page_table(pfns);
+ * device_page_table_unlock();
+ */
+bool hmm_vma_range_done(struct vm_area_struct *vma, struct hmm_range *range)
+{
+ unsigned long npages = (range->end - range->start) >> PAGE_SHIFT;
+ struct hmm *hmm;
+
+ if (range->end <= range->start) {
+ BUG();
+ return false;
+ }
+
+ hmm = hmm_register(vma->vm_mm);
+ if (!hmm) {
+ memset(range->pfns, 0, sizeof(*range->pfns) * npages);
+ return false;
+ }
+
+ spin_lock(&hmm->lock);
+ list_del_rcu(&range->list);
+ spin_unlock(&hmm->lock);
+
+ return range->valid;
+}
+EXPORT_SYMBOL(hmm_vma_range_done);
#endif /* IS_ENABLED(CONFIG_HMM_MIRROR) */
--
2.9.3