@@ -2257,7 +2257,7 @@ static inline bool cow_user_page(struct
bool ret;
void *kaddr;
void __user *uaddr;
- bool force_mkyoung;
+ bool locked = false;
struct vm_area_struct *vma = vmf->vma;
struct mm_struct *mm = vma->vm_mm;
unsigned long addr = vmf->address;
@@ -2282,11 +2282,11 @@ static inline bool cow_user_page(struct
* On architectures with software "accessed" bits, we would
* take a double page fault, so mark it accessed here.
*/
- force_mkyoung = arch_faults_on_old_pte() && !pte_young(vmf->orig_pte);
- if (force_mkyoung) {
+ if (arch_faults_on_old_pte() && !pte_young(vmf->orig_pte)) {
pte_t entry;
vmf->pte = pte_offset_map_lock(mm, vmf->pmd, addr, &vmf->ptl);
+ locked = true;
if (!likely(pte_same(*vmf->pte, vmf->orig_pte))) {
/*
* Other thread has already handled the fault
@@ -2310,18 +2310,37 @@ static inline bool cow_user_page(struct
* zeroes.
*/
if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE)) {
+ if (locked)
+ goto warn;
+
+ /* Re-validate under PTL if the page is still mapped */
+ vmf->pte = pte_offset_map_lock(mm, vmf->pmd, addr, &vmf->ptl);
+ locked = true;
+ if (!likely(pte_same(*vmf->pte, vmf->orig_pte))) {
+ /* The PTE changed under us. Retry page fault. */
+ ret = false;
+ goto pte_unlock;
+ }
+
/*
- * Give a warn in case there can be some obscure
- * use-case
+ * The same page can be mapped back since last copy attampt.
+ * Try to copy again under PTL.
*/
- WARN_ON_ONCE(1);
- clear_page(kaddr);
+ if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE)) {
+ /*
+ * Give a warn in case there can be some obscure
+ * use-case
+ */
+warn:
+ WARN_ON_ONCE(1);
+ clear_page(kaddr);
+ }
}
ret = true;
pte_unlock:
- if (force_mkyoung)
+ if (locked)
pte_unmap_unlock(vmf->pte, vmf->ptl);
kunmap_atomic(kaddr);
flush_dcache_page(dst);
The patch titled Subject: mm: avoid data corruption on CoW fault into PFN-mapped VMA has been removed from the -mm tree. Its filename was mm-avoid-data-corruption-on-cow-fault-into-pfn-mapped-vma.patch This patch was dropped because it was merged into mainline or a subsystem tree ------------------------------------------------------ From: "Kirill A. Shutemov" <kirill@shutemov.name> Subject: mm: avoid data corruption on CoW fault into PFN-mapped VMA Jeff Moyer has reported that one of xfstests triggers a warning when run on DAX-enabled filesystem: WARNING: CPU: 76 PID: 51024 at mm/memory.c:2317 wp_page_copy+0xc40/0xd50 ... wp_page_copy+0x98c/0xd50 (unreliable) do_wp_page+0xd8/0xad0 __handle_mm_fault+0x748/0x1b90 handle_mm_fault+0x120/0x1f0 __do_page_fault+0x240/0xd70 do_page_fault+0x38/0xd0 handle_page_fault+0x10/0x30 The warning happens on failed __copy_from_user_inatomic() which tries to copy data into a CoW page. This happens because of race between MADV_DONTNEED and CoW page fault: CPU0 CPU1 handle_mm_fault() do_wp_page() wp_page_copy() do_wp_page() madvise(MADV_DONTNEED) zap_page_range() zap_pte_range() ptep_get_and_clear_full() <TLB flush> __copy_from_user_inatomic() sees empty PTE and fails WARN_ON_ONCE(1) clear_page() The solution is to re-try __copy_from_user_inatomic() under PTL after checking that PTE is matches the orig_pte. The second copy attempt can still fail, like due to non-readable PTE, but there's nothing reasonable we can do about, except clearing the CoW page. Link: http://lkml.kernel.org/r/20200218154151.13349-1-kirill.shutemov@linux.intel.com Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Reported-by: Jeff Moyer <jmoyer@redhat.com> Tested-by: Jeff Moyer <jmoyer@redhat.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Justin He <Justin.He@arm.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> --- mm/memory.c | 35 +++++++++++++++++++++++++++-------- 1 file changed, 27 insertions(+), 8 deletions(-)