Re: [PATCH v2] mm/memory-failure: fix infinite UCE for VM_PFNMAP'ed page

[jane.chu@oracle.com]

On 8/10/2025 9:33 PM, Jinjiang Tu wrote:
> When memory_failure() is called for a already hwpoisoned pfn backed with
> struct page, kill_accessing_process() will conditionally send a SIGBUS to
> the current (triggering) process if it maps the page.
> 
> However, in case the page is not ordinarily mapped, but was mapped through
> remap_pfn_range(), kill_accessing_process() wouldn't identify it as mapped
> even though hwpoison_pte_range() would be prepared to handle it, because
> walk_page_range() will skip VM_PFNMAP as default in walk_page_test(). As
> a result, walk_page_range() will return 0, assuming "not mapped" and SIGBUS
> will be skipped. The user task will trigger UCE infinitely because it will
> not receive a SIGBUS on access and simply retry.
> 
> Before commit aaf99ac2ceb7 ("mm/hwpoison: do not send SIGBUS to processes
> with recovered clean pages"), kill_accessing_process() will return EFAULT.
> For x86, the current task will be killed in kill_me_maybe().
> 
> To fix it, add .test_walk callback for hwpoison_walk_ops to process
> VM_PFNMAP VMAs too.
> 
> Fixes: aaf99ac2ceb7 ("mm/hwpoison: do not send SIGBUS to processes with recovered clean pages")
> Signed-off-by: Jinjiang Tu <tujinjiang@huawei.com>
> ---
> Changelog since v1:
>   * update patch description, suggested by David Hildenbrand
> 
>   mm/memory-failure.c | 7 +++++++
>   1 file changed, 7 insertions(+)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index e2e685b971bb..fa6a8f2cdebc 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -853,9 +853,16 @@ static int hwpoison_hugetlb_range(pte_t *ptep, unsigned long hmask,
>   #define hwpoison_hugetlb_range	NULL
>   #endif
>   
> +static int hwpoison_test_walk(unsigned long start, unsigned long end,
> +			     struct mm_walk *walk)
> +{
> +	return 0;
> +}
> +
>   static const struct mm_walk_ops hwpoison_walk_ops = {
>   	.pmd_entry = hwpoison_pte_range,
>   	.hugetlb_entry = hwpoison_hugetlb_range,
> +	.test_walk = hwpoison_test_walk,
>   	.walk_lock = PGWALK_RDLOCK,
>   };
>   

Looks good.  Could you add this to stable ?

Reviewed-by: Jane Chu <jane.chu@oracle.com>

thanks,
-jane