linux-kernel - Re: [PATCH v12 12/22] mm: pagewalk: Allow walking without vma

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Message-ID: <CA+ZOyaiE2w686TmWWPT6tzu1MR3Fkm805k2hY1_VMfAnAwQPuQ@mail.gmail.com>
Date:   Thu, 24 Oct 2019 21:05:41 +0800
From:   Zong Li <zongbox@...il.com>
To:     Steven Price <steven.price@....com>
Cc:     linux-mm@...ck.org, Andy Lutomirski <luto@...nel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        James Morse <james.morse@....com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        linux-arm-kernel@...ts.infradead.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Mark Rutland <Mark.Rutland@....com>,
        "Liang, Kan" <kan.liang@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v12 12/22] mm: pagewalk: Allow walking without vma

Steven Price <steven.price@....com> 於 2019年10月19日 週六 下午4:12寫道：

>
> Since 48684a65b4e3: "mm: pagewalk: fix misbehavior of walk_page_range
> for vma(VM_PFNMAP)", page_table_walk() will report any kernel area as
> a hole, because it lacks a vma.
>
> This means each arch has re-implemented page table walking when needed,
> for example in the per-arch ptdump walker.
>
> Remove the requirement to have a vma except when trying to split huge
> pages.
>
> Signed-off-by: Steven Price <steven.price@....com>
> ---
>  mm/pagewalk.c | 25 +++++++++++++++++--------
>  1 file changed, 17 insertions(+), 8 deletions(-)
>
> diff --git a/mm/pagewalk.c b/mm/pagewalk.c
> index fc4d98a3a5a0..4139e9163aee 100644
> --- a/mm/pagewalk.c
> +++ b/mm/pagewalk.c
> @@ -38,7 +38,7 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,
>         do {
>  again:
>                 next = pmd_addr_end(addr, end);
> -               if (pmd_none(*pmd) || !walk->vma) {
> +               if (pmd_none(*pmd)) {
>                         if (ops->pte_hole)
>                                 err = ops->pte_hole(addr, next, walk);
>                         if (err)
> @@ -61,9 +61,14 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,
>                 if (!ops->pte_entry)
>                         continue;
>
> -               split_huge_pmd(walk->vma, pmd, addr);
> -               if (pmd_trans_unstable(pmd))
> -                       goto again;
> +               if (walk->vma) {
> +                       split_huge_pmd(walk->vma, pmd, addr);
> +                       if (pmd_trans_unstable(pmd))
> +                               goto again;
> +               } else if (pmd_leaf(*pmd)) {
> +                       continue;
> +               }
> +
>                 err = walk_pte_range(pmd, addr, next, walk);
>                 if (err)
>                         break;
> @@ -84,7 +89,7 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,
>         do {
>   again:
>                 next = pud_addr_end(addr, end);
> -               if (pud_none(*pud) || !walk->vma) {
> +               if (pud_none(*pud)) {
>                         if (ops->pte_hole)
>                                 err = ops->pte_hole(addr, next, walk);
>                         if (err)
> @@ -98,9 +103,13 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,
>                                 break;
>                 }
>
> -               split_huge_pud(walk->vma, pud, addr);
> -               if (pud_none(*pud))
> -                       goto again;
> +               if (walk->vma) {
> +                       split_huge_pud(walk->vma, pud, addr);
> +                       if (pud_none(*pud))
> +                               goto again;
> +               } else if (pud_leaf(*pud)) {
> +                       continue;
> +               }
>
>                 if (ops->pmd_entry || ops->pte_entry)
>                         err = walk_pmd_range(pud, addr, next, walk);
> --
> 2.20.1
>

It's good to me.

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