linux-kernel - Re: [PATCH] mm: Update mask post pxd_clear

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Message-ID:
 <GV1PR08MB105214AFCE69B0333DF65D3BCFBD22@GV1PR08MB10521.eurprd08.prod.outlook.com>
Date: Fri, 14 Mar 2025 14:27:38 +0000
From: Yeo Reum Yun <YeoReum.Yun@....com>
To: Dev Jain <Dev.Jain@....com>, "jroedel@...e.de" <jroedel@...e.de>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
CC: Ryan Roberts <Ryan.Roberts@....com>, "david@...hat.com"
	<david@...hat.com>, "willy@...radead.org" <willy@...radead.org>, "hch@....de"
	<hch@....de>, "linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH] mm: Update mask post pxd_clear_bad()

Hi Dev,

> > Since pxd_clear_bad() is an operation changing the state of the page tables,
> > we should call arch_sync_kernel_mappings() post this.
> >
> > Fixes: e80d3909be42 ("mm: track page table modifications in __apply_to_page_range()")
> > Cc: <stable@...r.kernel.org>
> > Signed-off-by: Dev Jain <dev.jain@....com>
> > ---
> >   mm/memory.c | 4 ++++
> >   1 file changed, 4 insertions(+)
> >
> > diff --git a/mm/memory.c b/mm/memory.c
> > index 78c7ee62795e..9a4a8c710be0 100644
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -2987,6 +2987,7 @@ static int apply_to_pmd_range(struct mm_struct *mm, pud_t *pud,
> >                       if (!create)
> >                               continue;
> >                       pmd_clear_bad(pmd);
> > +                     *mask = PGTBL_PMD_MODIFIED;
>
> Oh well, I guess these should have been *mask |= PGTBL_PMD_MODIFIED.
>
>
> >               }
> >               err = apply_to_pte_range(mm, pmd, addr, next,
> >                                        fn, data, create, mask);
> > @@ -3023,6 +3024,7 @@ static int apply_to_pud_range(struct mm_struct *mm, p4d_t *p4d,
> >                       if (!create)
> >                               continue;
> >                       pud_clear_bad(pud);
> > +                     *mask = PGTBL_PUD_MODIFIED;
> >               }
> >               err = apply_to_pmd_range(mm, pud, addr, next,
> >                                        fn, data, create, mask);
> > @@ -3059,6 +3061,7 @@ static int apply_to_p4d_range(struct mm_struct *mm, pgd_t *pgd,
> >                       if (!create)
> >                               continue;
> >                       p4d_clear_bad(p4d);
> > +                     *mask = PGTBL_P4D_MODIFIED;
> >               }
> >               err = apply_to_pud_range(mm, p4d, addr, next,
> >                                        fn, data, create, mask);
> > @@ -3095,6 +3098,7 @@ static int __apply_to_page_range(struct mm_struct *mm, unsigned long addr,
> >                       if (!create)
> >                               continue;
> >                       pgd_clear_bad(pgd);
> +                     mask = PGTBL_PGD_MODIFIED;
> >               }
> >               err = apply_to_p4d_range(mm, pgd, addr, next,
> >                                        fn, data, create, &mask);

I don't think this wouldn't need.
the pXd_clear_bad() is only called at creation of each level of page table,
and when it clear, the following, apply_to_pXd_range() function would be set
the make properly via pXd_alloc() and apply_to_pte_range().

Thanks.