linux-kernel - Re: [PATCH 1/1] mm: prevent poison consumption when splitting THP

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Message-ID: <CACw3F53kD_Toxwvb-WXsfhxLYwKovGoPKVV5z-_r6S77a=hH-A@mail.gmail.com>
Date: Sat, 11 Oct 2025 21:23:49 -0700
From: Jiaqi Yan <jiaqiyan@...gle.com>
To: Wei Yang <richard.weiyang@...il.com>
Cc: David Hildenbrand <david@...hat.com>, Qiuxu Zhuo <qiuxu.zhuo@...el.com>, akpm@...ux-foundation.org, 
	lorenzo.stoakes@...cle.com, linmiaohe@...wei.com, tony.luck@...el.com, 
	ziy@...dia.com, baolin.wang@...ux.alibaba.com, Liam.Howlett@...cle.com, 
	npache@...hat.com, ryan.roberts@....com, dev.jain@....com, baohua@...nel.org, 
	nao.horiguchi@...il.com, farrah.chen@...el.com, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, Andrew Zaborowski <andrew.zaborowski@...el.com>
Subject: Re: [PATCH 1/1] mm: prevent poison consumption when splitting THP

On Sat, Oct 11, 2025 at 6:37 PM Wei Yang <richard.weiyang@...il.com> wrote:
>
> On Mon, Sep 29, 2025 at 09:34:12AM +0200, David Hildenbrand wrote:
> >On 28.09.25 05:28, Qiuxu Zhuo wrote:
> [...]
> >
> >Hm, I wonder if we should actually check in try_to_map_unused_to_zeropage()
> >whether the page has the hwpoison flag set. Nothing wrong with scanning
> >non-affected pages.
> >
> >In thp_underused() we should just skip the folio entirely I guess, so keep
> >it simple.
> >
> >So what about something like this:
> >
> >diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> >index 9c38a95e9f091..d4109fd7fa1f2 100644
> >--- a/mm/huge_memory.c
> >+++ b/mm/huge_memory.c
> >@@ -4121,6 +4121,9 @@ static bool thp_underused(struct folio *folio)
> >        if (khugepaged_max_ptes_none == HPAGE_PMD_NR - 1)
> >                return false;
> >+       folio_contain_hwpoisoned_page(folio)
> >+               return false;
> >+
>
> One question.
>
> When hardware detect error, it would immediately trigger memory_failure()? Or
> it will wait until the memory is accessed?

Hardware detecting a memory error usually results in a poison
generation event. Kernel expects to receive such poison generation
event from modern platforms, then kicks off memory_failure without any
poison context, e.g. the current process cannot be assumed to be the
"culprit".

>
> >        for (i = 0; i < folio_nr_pages(folio); i++) {
> >                kaddr = kmap_local_folio(folio, i * PAGE_SIZE);
> >                if (!memchr_inv(kaddr, 0, PAGE_SIZE)) {
> >diff --git a/mm/migrate.c b/mm/migrate.c
> >index 9e5ef39ce73af..393fc2ffc96e5 100644
> >--- a/mm/migrate.c
> >+++ b/mm/migrate.c
> >@@ -305,8 +305,9 @@ static bool try_to_map_unused_to_zeropage(struct page_vma_mapped_walk *pvmw,
> >        pte_t newpte;
> >        void *addr;
> >-       if (PageCompound(page))
> >+       if (PageCompound(page) || PageHWPoison(page))
> >                return false;
> >+
> >        VM_BUG_ON_PAGE(!PageAnon(page), page);
> >        VM_BUG_ON_PAGE(!PageLocked(page), page);
> >        VM_BUG_ON_PAGE(pte_present(ptep_get(pvmw->pte)), page);
> >
> >
> >--
> >Cheers
> >
> >David / dhildenb
> >
>
> --
> Wei Yang
> Help you, Help me
>