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

[Miaohe Lin <linmiaohe@huawei.com>]

On 2025/8/11 12:33, 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
>  

It might be better to add a comment on why below hwpoison_test_walk is needed.
It looks somewhat weird as hwpoison_test_walk simply return 0.

> +static int hwpoison_test_walk(unsigned long start, unsigned long end,
> +			     struct mm_walk *walk)
> +{
> +	return 0;
> +}
> +

Anyway, this patch looks good to me.
Acked-by: Miaohe Lin <linmiaohe@huawei.com>

Thanks.
.