Re: [PATCH v2] mm: make page_mapped_in_vma() hugetlb walk aware

[David Hildenbrand <david@redhat.com>]

On 24.02.25 22:14, Jane Chu wrote:
> When a process consumes a UE in a page, the memory failure handler
> attempts to collect information for a potential SIGBUS.
> If the page is an anonymous page, page_mapped_in_vma(page, vma) is
> invoked in order to
>    1. retrieve the vaddr from the process' address space,
>    2. verify that the vaddr is indeed mapped to the poisoned page,
> where 'page' is the precise small page with UE.
> 
> It's been observed that when injecting poison to a non-head subpage
> of an anonymous hugetlb page, no SIGBUS show up; while injecting to
> the head page produces a SIGBUS. The casue is that, though hugetlb_walk()
> returns a valid pmd entry (on x86), but check_pte() detects mismatch
> between the head page per the pmd and the input subpage. Thus the vaddr
> is considered not mapped to the subpage and the process is not collected
> for SIGBUS purpose.  This is the calling stack
>        collect_procs_anon
>          page_mapped_in_vma
>            page_vma_mapped_walk
>              hugetlb_walk
>                huge_pte_lock
>                  check_pte
> 

Why can't we require callers to never pass in subpages of hugetlb pages, 
and sanity check that this is the case?


-- 
Cheers,

David / dhildenb