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mm: fix double page fault on arm64 if PTE_AF is cleared

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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):
[ffff9b007000] pgd=000000023d4f8003, pud=000000023da9b003,
               pmd=000000023d4b3003, pte=360000298607bd3

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 <justin.he@arm.com>
Reported-by: Yibo Cai <Yibo.Cai@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Jia He 2019-10-11 22:09:39 +08:00 committed by Catalin Marinas
parent f2c4e5970c
commit 83d116c530
1 changed files with 89 additions and 15 deletions
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104
mm/memory.c
View File

@ -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, &vmf->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 (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE)) {
/*
* 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.
* Give a warn in case there can be some obscure
* use-case
*/
if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE))
clear_page(kaddr);
kunmap_atomic(kaddr);
flush_dcache_page(dst);
} else
copy_user_highpage(dst, src, va, vma);
WARN_ON_ONCE(1);
clear_page(kaddr);
}
ret = true;
pte_unlock:
if (force_mkyoung)
pte_unmap_unlock(vmf->pte, vmf->ptl);
kunmap_atomic(kaddr);
flush_dcache_page(dst);
return ret;
}
static gfp_t __get_fault_gfp_mask(struct vm_area_struct *vma)
@ -2327,7 +2389,19 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)
vmf->address);
if (!new_page)
goto oom;
cow_user_page(new_page, old_page, vmf->address, vma);
if (!cow_user_page(new_page, old_page, vmf)) {
/*
* COW failed, if the fault was solved by other,
* it's fine. If not, userspace would re-fault on
* the same address and we will handle the fault
* from the second attempt.
*/
put_page(new_page);
if (old_page)
put_page(old_page);
return 0;
}
}
if (mem_cgroup_try_charge_delay(new_page, mm, GFP_KERNEL, &memcg, false))