Re: [v3 PATCH 2/5] mm: filemap: check if THP has hwpoisoned subpage for PMD page fault

[Naoya Horiguchi]

On Thu, Sep 30, 2021 at 02:53:08PM -0700, Yang Shi wrote:
> When handling shmem page fault the THP with corrupted subpage could be PMD
> mapped if certain conditions are satisfied.  But kernel is supposed to
> send SIGBUS when trying to map hwpoisoned page.
> 
> There are two paths which may do PMD map: fault around and regular fault.
> 
> Before commit f9ce0be71d1f ("mm: Cleanup faultaround and finish_fault() codepaths")
> the thing was even worse in fault around path.  The THP could be PMD mapped as
> long as the VMA fits regardless what subpage is accessed and corrupted.  After
> this commit as long as head page is not corrupted the THP could be PMD mapped.
> 
> In the regular fault path the THP could be PMD mapped as long as the corrupted
> page is not accessed and the VMA fits.
> 
> This loophole could be fixed by iterating every subpage to check if any
> of them is hwpoisoned or not, but it is somewhat costly in page fault path.
> 
> So introduce a new page flag called HasHWPoisoned on the first tail page.  It
> indicates the THP has hwpoisoned subpage(s).  It is set if any subpage of THP
> is found hwpoisoned by memory failure and cleared when the THP is freed or
> split.
> 
> Fixes: 800d8c63b2e9 ("shmem: add huge pages support")
> Cc: <stable@xxxxxxxxxxxxxxx>
> Suggested-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Signed-off-by: Yang Shi <shy828301@xxxxxxxxx>
...
> @@ -668,6 +673,20 @@ PAGEFLAG_FALSE(DoubleMap)
>  	TESTSCFLAG_FALSE(DoubleMap)
>  #endif
>  
> +#if defined(CONFIG_MEMORY_FAILURE) && defined(CONFIG_TRANSPARENT_HUGEPAGE)
> +/*
> + * PageHasPoisoned indicates that at least on subpage is hwpoisoned in the

Maybe you meant as follow?

+ * PageHasHWPoisoned indicates that at least one subpage is hwpoisoned in the

Thanks,
Naoya Horiguchi