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

[Jiaqi Yan]

On Mon, Sep 29, 2025 at 6:57 AM Zhuo, Qiuxu <qiuxu.zhuo@xxxxxxxxx> wrote:
>
> Hi Miaohe,
>
> > From: Miaohe Lin <linmiaohe@xxxxxxxxxx>
> > [...]
> > >>   First Machine Check occurs // [1]
> > >>     memory_failure()         // [2]
> > >>       try_to_split_thp_page()
> > >>         split_huge_page()
> > >>           split_huge_page_to_list_to_order()
> > >>             __folio_split()  // [3]
> > >>               remap_page()
> > >>                 remove_migration_ptes()
> > >>                   remove_migration_pte()
> > >>                     try_to_map_unused_to_zeropage()
> > >
> > > Just an observation: Unfortunately THP only has PageHasHWPoisoned and
> > > don't know the exact HWPoisoned page. Otherwise, we may still use
> > > zeropage for these not HWPoisoned.
> >
> > IIUC, the raw error page will have HWPoisoned flag set while the THP has
> > PageHasHWPoisoned set. So I think we could use zeropage for healthy sub-
> > pages.

Oh, sorry, somehow I forgot this so I thought there is no better place
to do the HWPoison check than in __folio_split. Yeah, since we know
the exact raw error page, checking in try_to_map_unused_to_zeropage
like David suggested is much better!

>
> Good point.
>
> David's suggested diff in another e-mail checked the raw error page instead of
> entire folio. And I tested that diff and it worked well.
>
> -Qiuxu