On 2022/7/14 8:20, Axel Rasmussen wrote:
> On Wed, Jul 13, 2022 at 4:36 PM Mike Kravetz <mike.kravetz@xxxxxxxxxx> wrote:
>>
>> On 07/13/22 15:46, Axel Rasmussen wrote:
>>> I think there is a small mistake in this patch.
>>>
>>> Consider the non-minor-fault case. We have this block:
>>>
>>> /* Add shared, newly allocated pages to the page cache. */
>>> if (vm_shared && !is_continue) {
>>> /* ... */
>>> }
>>>
>>> In here, we've added the newly allocated page to the page cache, and
>>> we've set this page_in_pagecache flag to true. But we *do not* setup
>>> rmap for this page in this block. I think in this case, the patch will
>>> cause us to do the wrong thing: we should hugepage_add_new_anon_rmap()
>>> further down, but with this patch we dup instead.
>>
>> I am not sure I follow. The patch from Miaohe Lin would not change any
>> behavior in the 'if (vm_shared && !is_continue)' case. In this case
>> both vm_shared and page_in_pagecache are true.
>>
>> IIUC, the patch would address the case where !vm_shared && is_continue.
>
> Ah, you're right, my interpretation of the various flags got mixed up
> somewhere along the way.
>
> page_in_pagecache is equivalent to vm_shared in this function,
> *except* when we have is_continue. Given that, I think this patch is
> correct in the vm_shared case (no behavior change). In case of
> !vm_shared && is_continue, I agree the patch is a correction to the
> previous behavior.
>
>>
>> On 07/12/22 21:05, Miaohe Lin wrote:
>>> In MCOPY_ATOMIC_CONTINUE case with a non-shared VMA, pages in the page
>>> cache are installed in the ptes. But hugepage_add_new_anon_rmap is called
>>> for them mistakenly because they're not vm_shared. This will corrupt the
>>> page->mapping used by page cache code.
>>>
>>> Fixes: f619147104c8 ("userfaultfd: add UFFDIO_CONTINUE ioctl")
>>> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
>>> ---
>>> mm/hugetlb.c | 2 +-
>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>>> index 8d379e03f672..b232e1508e49 100644
>>> --- a/mm/hugetlb.c
>>> +++ b/mm/hugetlb.c
>>> @@ -6038,7 +6038,7 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
>>> if (!huge_pte_none_mostly(huge_ptep_get(dst_pte)))
>>> goto out_release_unlock;
>>>
>>> - if (vm_shared) {
>>> + if (page_in_pagecache) {
>>> page_dup_file_rmap(page, true);
Many thanks for your comments.
As discussed in another thread, we might call page_dup_file_rmap for newly
allocated page (regardless of this patch). So should we come up a seperate
patch to call page_add_file_rmap here instead?
Thanks.
>>> } else {
>>> ClearHPageRestoreReserve(page);
>>
>> --
>> Mike Kravetz
> .
>
