linux-kernel - Re: [PATCH] mm: introduce arch_has_hw_pmd

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Date:   Mon, 21 Nov 2022 02:51:59 -0700
From:   Yu Zhao <yuzhao@...gle.com>
To:     Juergen Gross <jgross@...e.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org, linux-mm@...ck.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Sander Eikelenboom <linux@...elenboom.it>
Subject: Re: [PATCH] mm: introduce arch_has_hw_pmd_young()

On Mon, Nov 21, 2022 at 2:50 AM Juergen Gross <jgross@...e.com> wrote:
>
> On 21.11.22 10:32, Juergen Gross wrote:
> > When running as a Xen PV guests commit eed9a328aa1a ("mm: x86: add
> > CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG") can cause a protection violation
> > in pmdp_test_and_clear_young():
> >
> >   BUG: unable to handle page fault for address: ffff8880083374d0
> >   #PF: supervisor write access in kernel mode
> >   #PF: error_code(0x0003) - permissions violation
> >   PGD 3026067 P4D 3026067 PUD 3027067 PMD 7fee5067 PTE 8010000008337065
> >   Oops: 0003 [#1] PREEMPT SMP NOPTI
> >   CPU: 7 PID: 158 Comm: kswapd0 Not tainted 6.1.0-rc5-20221118-doflr+ #1
> >   RIP: e030:pmdp_test_and_clear_young+0x25/0x40
> >
> > This happens because the Xen hypervisor can't emulate direct writes to
> > page table entries other than PTEs.
> >
> > This can easily be fixed by introducing arch_has_hw_pmd_young()
> > similar to arch_has_hw_pte_young() and test that instead of
> > CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG.
>
> I just spotted that I missed to update my commit message to match the
> patch:
>
> s/arch_has_hw_pmd_young/arch_has_hw_nonleaf_pmd_young/
>
> I'll wait with a resend in order to get some feedback first.

Thanks. For the next spin:

Acked-by: Yu Zhao <yuzhao@...gle.com>