linux-kernel - Re: [PATCH 1/3] mm/debug_vm_pgtable: remove pte entry from the page table

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Date:   Thu, 20 Jan 2022 10:19:50 -0500
From:   Zi Yan <ziy@...dia.com>
To:     Pasha Tatashin <pasha.tatashin@...een.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, rientjes@...gle.com, pjt@...gle.com,
        weixugc@...gle.com, gthelen@...gle.com, mingo@...hat.com,
        will@...nel.org, rppt@...nel.org, dave.hansen@...ux.intel.com,
        hpa@...or.com, aneesh.kumar@...ux.ibm.com, jirislaby@...nel.org,
        songmuchun@...edance.com, qydwhotmail@...il.com, hughd@...gle.com,
        anshuman.khandual@....com
Subject: Re: [PATCH 1/3] mm/debug_vm_pgtable: remove pte entry from the page table

On 19 Jan 2022, at 23:25, Pasha Tatashin wrote:

> The pte entry that is used in pte_advanced_tests() is never removed from
> the page table at the end of the test.
>
> The issue is detected by page_table_check, to repro compile kernel with
> the following configs:
>
> CONFIG_DEBUG_VM_PGTABLE=y
> CONFIG_PAGE_TABLE_CHECK=y
> CONFIG_PAGE_TABLE_CHECK_ENFORCED=y
>
> During the boot the following BUG is printed:
>
> [    7.483050][    T1] debug_vm_pgtable: [debug_vm_pgtable         ]:
> Validating architecture page tabs
> [    7.490930][    T1] ------------[ cut here ]------------
> [    7.494926][    T1] kernel BUG at mm/page_table_check.c:194!
> [    7.499172][    T1] invalid opcode: 0000 [#1] PREEMPT SMP KASAN
> [    7.503610][    T1] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.16.0+
> [    7.508600][    T1] Hardware name: QEMU Standard PC (i440FX + PIIX,
> ...
>
> The entry should be properly removed from the page table before the page
> is released to the free list.
>
> Fixes: a5c3b9ffb0f4 ("mm/debug_vm_pgtable: add tests validating advanced arch page table helpers")
>
> Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
> ---
>  mm/debug_vm_pgtable.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
> index a7ac97c76762..f7c5970f1719 100644
> --- a/mm/debug_vm_pgtable.c
> +++ b/mm/debug_vm_pgtable.c
> @@ -171,6 +171,7 @@ static void __init pte_advanced_tests(struct pgtable_debug_args *args)
>  	ptep_test_and_clear_young(args->vma, args->vaddr, args->ptep);
>  	pte = ptep_get(args->ptep);
>  	WARN_ON(pte_young(pte));
> +	ptep_get_and_clear_full(args->mm, args->vaddr, args->ptep, 1);
>  }
>
>  static void __init pte_savedwrite_tests(struct pgtable_debug_args *args)
> -- 
> 2.34.1.703.g22d0c6ccf7-goog

LGTM. Thanks.

Reviewed-by: Zi Yan <ziy@...dia.com> and Tested-by: Zi Yan <ziy@...dia.com>

--
Best Regards,
Yan, Zi

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