When we tested pmdk unit test [1] vmmalloc_fork TEST3 on arm64 guest, there
will be a double page fault in __copy_from_user_inatomic of cow_user_page.
To reproduce the bug, the cmd is as follows after you deployed everything:
make -C src/test/vmmalloc_fork/ TEST_TIME=60m check
Below call trace is from arm64 do_page_fault for debugging purpose:
[ 110.016195] Call trace:
[ 110.016826] do_page_fault+0x5a4/0x690
[ 110.017812] do_mem_abort+0x50/0xb0
[ 110.018726] el1_da+0x20/0xc4
[ 110.019492] __arch_copy_from_user+0x180/0x280
[ 110.020646] do_wp_page+0xb0/0x860
[ 110.021517] __handle_mm_fault+0x994/0x1338
[ 110.022606] handle_mm_fault+0xe8/0x180
[ 110.023584] do_page_fault+0x240/0x690
[ 110.024535] do_mem_abort+0x50/0xb0
[ 110.025423] el0_da+0x20/0x24
The pte info before __copy_from_user_inatomic is (PTE_AF is cleared):
[9b007000] pgd=00023d4f8003, pud=00023da9b003,
pmd=00023d4b3003, pte=36298607bd3
As told by Catalin: "On arm64 without hardware Access Flag, copying from
user will fail because the pte is old and cannot be marked young. So we
always end up with zeroed page after fork() + CoW for pfn mappings. we
don't always have a hardware-managed access flag on arm64."
This patch fixes it by calling pte_mkyoung. Also, the parameter is
changed because vmf should be passed to cow_user_page()
Add a WARN_ON_ONCE when __copy_from_user_inatomic() returns error
in case there can be some obscure use-case (by Kirill).
[1] https://github.com/pmem/pmdk/tree/master/src/test/vmmalloc_fork
Signed-off-by: Jia He
Reported-by: Yibo Cai
Reviewed-by: Catalin Marinas
Acked-by: Kirill A. Shutemov
---
mm/memory.c | 104
1 file changed, 89 insertions(+), 15 deletions(-)
diff --git a/mm/memory.c b/mm/memory.c
index b1ca51a079f2..b6a5d6a08438 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -118,6 +118,18 @@ int randomize_va_space __read_mostly =
2;
#endif
+#ifndef arch_faults_on_old_pte
+static inline bool arch_faults_on_old_pte(void)
+{
+ /*
+* Those arches which don't have hw access flag feature need to
+* implement their own helper. By default, "true" means pagefault
+* will be hit on old pte.
+*/
+ return true;
+}
+#endif
+
static int __init disable_randmaps(char *s)
{
randomize_va_space = 0;
@@ -2145,32 +2157,82 @@ static inline int pte_unmap_same(struct mm_struct *mm,
pmd_t *pmd,
return same;
}
-static inline void cow_user_page(struct page *dst, struct page *src, unsigned
long va, struct vm_area_struct *vma)
+static inline bool cow_user_page(struct page *dst, struct page *src,
+struct vm_fault *vmf)
{
+ bool ret;
+ void *kaddr;
+ void __user *uaddr;
+ bool force_mkyoung;
+ struct vm_area_struct *vma = vmf->vma;
+ struct mm_struct *mm = vma->vm_mm;
+ unsigned long addr = vmf->address;
+
debug_dma_assert_idle(src);
+ if (likely(src)) {
+ copy_user_highpage(dst, src, addr, vma);
+ return true;
+ }
+
/*
* If the source page was a PFN mapping, we don't have
* a "struct page" for it. We do a best-effort copy by
* just copying from the original user address. If that
* fails, we just zero-fill it. Live with it.
*/
- if (unlikely(!src)) {
- void *kaddr = kmap_atomic(dst);
- void __user *uaddr = (void __user *)(va & PAGE_MASK);
+ kaddr = kmap_atomic(dst);
+ uaddr = (void __user *)(addr & PAGE_MASK);
+
+ /*
+* 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) {
+ pte_t entry;
+
+ vmf->pte = pte_offset_map_lock(mm, vmf->pmd, addr, >ptl);
+ if (!likely(pte_same(*vmf->pte, vmf->orig_pte))) {
+ /*
+* Other thread has already handled the fault
+* and we don't need to do anything. If it's
+* not the case, the fault will be triggered
+* again on the same address.
+*/
+ ret = false;
+ goto pte_unlock;
+ }
+ entry = pte_mkyoung(vmf->orig_pte);
+ if (ptep_set_access_flags(vma, addr, vmf->pte, entry, 0))
+ update_mmu_cache(vma, addr, vmf->pte);
+ }
+
+ /*
+* This really shouldn't fail, because the page is there
+* in the page tables. But it might just be unreadable,
+* in which case we just give up and fill the result with
+* zeroes.
+*/
+ if
