linux-kernel - Re: [PATCH 2/2] arm64/mm: fix incorrect file_map

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Message-ID: <CA+CK2bAHD2oj1SbdrLTQnEs5E7Cp=D=7c0AVG6bU3Nr+_NK15w@mail.gmail.com>
Date:   Wed, 16 Nov 2022 10:18:51 -0500
From:   Pasha Tatashin <pasha.tatashin@...een.com>
To:     Liu Shixin <liushixin2@...wei.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        David Hildenbrand <dhildenb@...hat.com>,
        Rafael Aquini <raquini@...hat.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] arm64/mm: fix incorrect file_map_count for invalid pmd/pud

On Wed, Nov 16, 2022 at 2:51 AM Liu Shixin <liushixin2@...wei.com> wrote:
>
> The page table check trigger BUG_ON() unexpectedly when split hugepage:
>
>  ------------[ cut here ]------------
>  kernel BUG at mm/page_table_check.c:119!
>  Internal error: Oops - BUG: 00000000f2000800 [#1] SMP
>  Dumping ftrace buffer:
>     (ftrace buffer empty)
>  Modules linked in:
>  CPU: 7 PID: 210 Comm: transhuge-stres Not tainted 6.1.0-rc3+ #748
>  Hardware name: linux,dummy-virt (DT)
>  pstate: 20000005 (nzCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
>  pc : page_table_check_set.isra.0+0x398/0x468
>  lr : page_table_check_set.isra.0+0x1c0/0x468
> [...]
>  Call trace:
>   page_table_check_set.isra.0+0x398/0x468
>   __page_table_check_pte_set+0x160/0x1c0
>   __split_huge_pmd_locked+0x900/0x1648
>   __split_huge_pmd+0x28c/0x3b8
>   unmap_page_range+0x428/0x858
>   unmap_single_vma+0xf4/0x1c8
>   zap_page_range+0x2b0/0x410
>   madvise_vma_behavior+0xc44/0xe78
>   do_madvise+0x280/0x698
>   __arm64_sys_madvise+0x90/0xe8
>   invoke_syscall.constprop.0+0xdc/0x1d8
>   do_el0_svc+0xf4/0x3f8
>   el0_svc+0x58/0x120
>   el0t_64_sync_handler+0xb8/0xc0
>   el0t_64_sync+0x19c/0x1a0
> [...]
>
> On arm64, pmd_present() will return true even if the pmd is invalid.
> in pmdp_invalidate() the file_map_count will not only decrease once but
> also increase once. Then in set_pte_at(), the file_map_count increase
> again, and so trigger BUG_ON() unexpectedly.

>  static inline bool pmd_user_accessible_page(pmd_t pmd)
>  {
> -       return pmd_leaf(pmd) && (pmd_user(pmd) || pmd_user_exec(pmd));
> +       return pmd_leaf(pmd) && (pmd_user(pmd) || pmd_user_exec(pmd)) && pmd_valid(pmd);
>  }
>
>  static inline bool pud_user_accessible_page(pud_t pud)
>  {
> -       return pud_leaf(pud) && pud_user(pud);
> +       return pud_leaf(pud) && pud_user(pud) && pud_valid(pud);

This looks closer to x86 where the check is directly: pmd_val(pmd) &
_PAGE_PRESENT, without PTE_PROT_NONE that is part of pmd_present()

Acked-by: Pasha Tatashin <pasha.tatashin@...een.com>

Thanks,
Pasha