linux-kernel - Re: [PATCH v2] mm: make page_mapped_in

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Message-ID: <3f3acf9f-f71d-77a3-ca61-5cc5c6c7f02b@huawei.com>
Date: Tue, 25 Feb 2025 14:49:56 +0800
From: Miaohe Lin <linmiaohe@...wei.com>
To: Jane Chu <jane.chu@...cle.com>
CC: <willy@...radead.org>, <peterx@...hat.com>, <akpm@...ux-foundation.org>,
	<kirill.shutemov@...ux.intel.com>, <hughd@...gle.com>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] mm: make page_mapped_in_vma() hugetlb walk aware

On 2025/2/25 5:14, 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
> 
> check_pte() header says that it
> "check if [pvmw->pfn, @pvmw->pfn + @pvmw->nr_pages) is mapped at the @pvmw->pte"
> but practically works only if pvmw->pfn is the head page pfn at pvmw->pte.
> Hindsight acknowledging that some pvmw->pte could point to a hugepage of
> some sort such that it makes sense to make check_pte() work for hugepage.

Thanks for your patch. This patch looks good to me.

> 
> Signed-off-by: Jane Chu <jane.chu@...cle.com>

Is a Fixes tag needed?

Thanks.
.