mm: make pte_unmap_same compatible with SPF
pte_unmap_same() is making the assumption that the page table are still
around because the mmap_sem is held.
This is no more the case when running a speculative page fault and
additional check must be made to ensure that the final page table are still
there.
This is now done by calling pte_spinlock() to check for the VMA's
consistency while locking for the page tables.
This is requiring passing a vm_fault structure to pte_unmap_same() which is
containing all the needed parameters.
As pte_spinlock() may fail in the case of a speculative page fault, if the
VMA has been touched in our back, pte_unmap_same() should now return 3
cases :
1. pte are the same (0)
2. pte are different (VM_FAULT_PTNOTSAME)
3. a VMA's changes has been detected (VM_FAULT_RETRY)
The case 2 is handled by the introduction of a new VM_FAULT flag named
VM_FAULT_PTNOTSAME which is then trapped in cow_user_page().
If VM_FAULT_RETRY is returned, it is passed up to the callers to retry the
page fault while holding the mmap_sem.
Change-Id: Iaccfa0d877334f4343f8b0ec3400af5070ff5864
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Patch-mainline: linux-mm @ Tue, 17 Apr 2018 16:33:12
[vinmenon@codeaurora.org: 4.9 porting changes]
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>
diff --git a/mm/memory.c b/mm/memory.c
index 8a56b3f..4fa2c30 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1984,21 +1984,30 @@
* parts, do_swap_page must check under lock before unmapping the pte and
* proceeding (but do_wp_page is only called after already making such a check;
* and do_anonymous_page can safely check later on).
+ *
+ * pte_unmap_same() returns:
+ * 0 if the PTE are the same
+ * VM_FAULT_PTNOTSAME if the PTE are different
+ * VM_FAULT_RETRY if the VMA has changed in our back during
+ * a speculative page fault handling.
*/
-static inline int pte_unmap_same(struct mm_struct *mm, pmd_t *pmd,
- pte_t *page_table, pte_t orig_pte)
+static inline int pte_unmap_same(struct mm_struct *mm, struct fault_env *fe,
+ pte_t orig_pte)
{
- int same = 1;
+ int ret = 0;
+
#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT)
if (sizeof(pte_t) > sizeof(unsigned long)) {
- spinlock_t *ptl = pte_lockptr(mm, pmd);
- spin_lock(ptl);
- same = pte_same(*page_table, orig_pte);
- spin_unlock(ptl);
+ if (pte_spinlock(mm, fe)) {
+ if (!pte_same(*fe->pte, orig_pte))
+ ret = VM_FAULT_PTNOTSAME;
+ spin_unlock(fe->ptl);
+ } else
+ ret = VM_FAULT_RETRY;
}
#endif
- pte_unmap(page_table);
- return same;
+ pte_unmap(fe->pte);
+ return ret;
}
static inline void cow_user_page(struct page *dst, struct page *src, unsigned long va, struct vm_area_struct *vma)
@@ -2548,9 +2557,17 @@
int exclusive = 0;
int ret = 0;
- if (!pte_unmap_same(vma->vm_mm, fe->pmd, fe->pte, orig_pte))
+ ret = pte_unmap_same(vma->vm_mm, fe, orig_pte);
+ if (ret) {
+ /*
+ * If pte != orig_pte, this means another thread did the
+ * swap operation in our back.
+ * So nothing else to do.
+ */
+ if (ret == VM_FAULT_PTNOTSAME)
+ ret = 0;
goto out;
-
+ }
entry = pte_to_swp_entry(orig_pte);
if (unlikely(non_swap_entry(entry))) {
if (is_migration_entry(entry)) {