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References: <20191018101248.33727-1-steven.price@arm.com> <20191018101248.33727-14-steven.price@arm.com>
In-Reply-To: <20191018101248.33727-14-steven.price@arm.com>
From:   Zong Li <zongbox@gmail.com>
Date:   Thu, 24 Oct 2019 21:06:25 +0800
Message-ID: <CA+ZOyahE7Z8jw60iu__wE5eeBSvmE57eAY8XY4q3fDdJb6gDrQ@mail.gmail.com>
Subject: Re: [PATCH v12 13/22] mm: pagewalk: Add test_p?d callbacks
To:     Steven Price <steven.price@arm.com>
Cc:     linux-mm@kvack.org, Andy Lutomirski <luto@kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Arnd Bergmann <arnd@arndb.de>, Borislav Petkov <bp@alien8.de>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Ingo Molnar <mingo@redhat.com>,
        James Morse <james.morse@arm.com>,
        =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= <jglisse@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Will Deacon <will@kernel.org>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>,
        linux-arm-kernel@lists.infradead.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Mark Rutland <Mark.Rutland@arm.com>,
        "Liang, Kan" <kan.liang@linux.intel.com>,
        Andrew Morton <akpm@linux-foundation.org>
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Steven Price <steven.price@arm.com> =E6=96=BC 2019=E5=B9=B410=E6=9C=8819=E6=
=97=A5 =E9=80=B1=E5=85=AD =E4=B8=8B=E5=8D=884:12=E5=AF=AB=E9=81=93=EF=BC=9A
>
> It is useful to be able to skip parts of the page table tree even when
> walking without VMAs. Add test_p?d callbacks similar to test_walk but
> which are called just before a table at that level is walked. If the
> callback returns non-zero then the entire table is skipped.
>
> Signed-off-by: Steven Price <steven.price@arm.com>
> ---
>  include/linux/pagewalk.h | 11 +++++++++++
>  mm/pagewalk.c            | 24 ++++++++++++++++++++++++
>  2 files changed, 35 insertions(+)
>
> diff --git a/include/linux/pagewalk.h b/include/linux/pagewalk.h
> index 12004b097eae..df424197a25a 100644
> --- a/include/linux/pagewalk.h
> +++ b/include/linux/pagewalk.h
> @@ -24,6 +24,11 @@ struct mm_walk;
>   *                     "do page table walk over the current vma", return=
ing
>   *                     a negative value means "abort current page table =
walk
>   *                     right now" and returning 1 means "skip the curren=
t vma"
> + * @test_pmd:          similar to test_walk(), but called for every pmd.
> + * @test_pud:          similar to test_walk(), but called for every pud.
> + * @test_p4d:          similar to test_walk(), but called for every p4d.
> + *                     Returning 0 means walk this part of the page tabl=
es,
> + *                     returning 1 means to skip this range.
>   *
>   * p?d_entry callbacks are called even if those levels are folded on a
>   * particular architecture/configuration.
> @@ -46,6 +51,12 @@ struct mm_walk_ops {
>                              struct mm_walk *walk);
>         int (*test_walk)(unsigned long addr, unsigned long next,
>                         struct mm_walk *walk);
> +       int (*test_pmd)(unsigned long addr, unsigned long next,
> +                       pmd_t *pmd_start, struct mm_walk *walk);
> +       int (*test_pud)(unsigned long addr, unsigned long next,
> +                       pud_t *pud_start, struct mm_walk *walk);
> +       int (*test_p4d)(unsigned long addr, unsigned long next,
> +                       p4d_t *p4d_start, struct mm_walk *walk);
>  };
>
>  /**
> diff --git a/mm/pagewalk.c b/mm/pagewalk.c
> index 4139e9163aee..43acffefd43f 100644
> --- a/mm/pagewalk.c
> +++ b/mm/pagewalk.c
> @@ -34,6 +34,14 @@ static int walk_pmd_range(pud_t *pud, unsigned long ad=
dr, unsigned long end,
>         const struct mm_walk_ops *ops =3D walk->ops;
>         int err =3D 0;
>
> +       if (ops->test_pmd) {
> +               err =3D ops->test_pmd(addr, end, pmd_offset(pud, 0UL), wa=
lk);
> +               if (err < 0)
> +                       return err;
> +               if (err > 0)
> +                       return 0;
> +       }
> +
>         pmd =3D pmd_offset(pud, addr);
>         do {
>  again:
> @@ -85,6 +93,14 @@ static int walk_pud_range(p4d_t *p4d, unsigned long ad=
dr, unsigned long end,
>         const struct mm_walk_ops *ops =3D walk->ops;
>         int err =3D 0;
>
> +       if (ops->test_pud) {
> +               err =3D ops->test_pud(addr, end, pud_offset(p4d, 0UL), wa=
lk);
> +               if (err < 0)
> +                       return err;
> +               if (err > 0)
> +                       return 0;
> +       }
> +
>         pud =3D pud_offset(p4d, addr);
>         do {
>   again:
> @@ -128,6 +144,14 @@ static int walk_p4d_range(pgd_t *pgd, unsigned long =
addr, unsigned long end,
>         const struct mm_walk_ops *ops =3D walk->ops;
>         int err =3D 0;
>
> +       if (ops->test_p4d) {
> +               err =3D ops->test_p4d(addr, end, p4d_offset(pgd, 0UL), wa=
lk);
> +               if (err < 0)
> +                       return err;
> +               if (err > 0)
> +                       return 0;
> +       }
> +
>         p4d =3D p4d_offset(pgd, addr);
>         do {
>                 next =3D p4d_addr_end(addr, end);
> --
> 2.20.1
>

It's good to me.

Tested-by: Zong Li <zong.li@sifive.com>