On 2023/7/15 11:50, Matthew Wilcox wrote:
> On Sat, Jul 15, 2023 at 11:17:26AM +0800, Miaohe Lin wrote:
>> Hwpoisoned dirty swap cache page is kept in the swap cache and there's
>> simple interception code in do_swap_page() to catch it. But when trying
>> to swapoff, unuse_pte() will wrongly install a general sense of "future
>> accesses are invalid" swap entry for hwpoisoned swap cache page due to
>> unaware of such type of page. The user will receive SIGBUS signal without
>> expected BUS_MCEERR_AR payload.
>
> Have you observed this, or do you just think it's true?
>
>> +++ b/mm/swapfile.c
>> @@ -1767,7 +1767,8 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
>> swp_entry_t swp_entry;
>>
>> dec_mm_counter(vma->vm_mm, MM_SWAPENTS);
>> - if (hwposioned) {
>> + /* Hwpoisoned swapcache page is also !PageUptodate. */
>> + if (hwposioned || PageHWPoison(page)) {
>
> This line makes no sense to me. How do we get here with PageHWPoison()
> being true and hwposioned being false?
hwposioned will be true iff ksm_might_need_to_copy returns -EHWPOISON.
And there's PageUptodate check in ksm_might_need_to_copy before we can return -EHWPOISON:
ksm_might_need_to_copy
if (!PageUptodate(page))
return page; /* let do_swap_page report the error */
^^^
Will return here because hwpoisoned swapcache page is !PageUptodate(cleared via me_swapcache_dirty()).
Or am I miss something?
Thanks.
