On x86 memory accesses to pages without the ACCESSED flag set result in the
ACCESSED flag being set automatically. With the ARM architecture a page access
fault is raised instead (and it will continue to be raised until the ACCESSED
flag is set for the appropriate PTE/PMD).
For normal memory pages, handle_pte_fault will call pte_mkyoung (effectively
setting the ACCESSED flag). For transparent huge pages, pmd_mkyoung will only
be called for a write fault.
This patch ensures that faults on transparent hugepages which do not result
in a CoW update the access flags for the faulting pmd.
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Chris Metcalf <cmetcalf@xxxxxxxxxx>
Signed-off-by: Steve Capper <steve.capper@xxxxxxx>
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
---
v2: - Use pmd_trans_huge_lock to guard against splitting pmds
- Propogate dirty (write) flag to low-level pmd modifier
include/linux/huge_mm.h | 2 ++
mm/huge_memory.c | 8 ++++++++
mm/memory.c | 9 ++++++++-
3 files changed, 18 insertions(+), 1 deletions(-)
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 4c59b11..5eb9b06 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -8,6 +8,8 @@ extern int do_huge_pmd_anonymous_page(struct mm_struct *mm,
extern int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
pmd_t *dst_pmd, pmd_t *src_pmd, unsigned long addr,
struct vm_area_struct *vma);
+extern void huge_pmd_set_accessed(struct vm_area_struct *vma,
+ unsigned long address, pmd_t *pmd, int dirty);
extern int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
unsigned long address, pmd_t *pmd,
pmd_t orig_pmd);
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index d684934..1de3f9b 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -914,6 +914,14 @@ out_free_pages:
goto out;
}
+void huge_pmd_set_accessed(struct vm_area_struct *vma, unsigned long address,
+ pmd_t *pmd, int dirty)
+{
+ pmd_t entry = pmd_mkyoung(*pmd);
+ if (pmdp_set_access_flags(vma, address & HPAGE_PMD_MASK, pmd, entry, dirty))
+ update_mmu_cache(vma, address, pmd);
+}
+
int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
unsigned long address, pmd_t *pmd, pmd_t orig_pmd)
{
diff --git a/mm/memory.c b/mm/memory.c
index 5736170..f12f859 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3524,7 +3524,8 @@ retry:
barrier();
if (pmd_trans_huge(orig_pmd)) {
- if (flags & FAULT_FLAG_WRITE &&
+ int dirty = flags & FAULT_FLAG_WRITE;
+ if (dirty &&
!pmd_write(orig_pmd) &&
!pmd_trans_splitting(orig_pmd)) {
ret = do_huge_pmd_wp_page(mm, vma, address, pmd,
@@ -3537,7 +3538,13 @@ retry:
if (unlikely(ret & VM_FAULT_OOM))
goto retry;
return ret;
+ } else if (pmd_trans_huge_lock(pmd, vma) == 1) {
+ if (likely(pmd_same(*pmd, orig_pmd)))
+ huge_pmd_set_accessed(vma, address, pmd,
+ dirty);
+ spin_unlock(&mm->page_table_lock);
}
+
return 0;
}
}
--
1.7.4.1
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