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Subject: Re: [PATCH v5 1/4] mm/debug_vm_pgtable: remove pte entry from the
 page table
To:     Pasha Tatashin <pasha.tatashin@soleen.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        akpm@linux-foundation.org, rientjes@google.com, pjt@google.com,
        weixugc@google.com, gthelen@google.com, mingo@redhat.com,
        will@kernel.org, rppt@kernel.org, dave.hansen@linux.intel.com,
        hpa@zytor.com, aneesh.kumar@linux.ibm.com, jirislaby@kernel.org,
        songmuchun@bytedance.com, qydwhotmail@gmail.com, hughd@google.com,
        ziy@nvidia.com
References: <20220131203249.2832273-1-pasha.tatashin@soleen.com>
 <20220131203249.2832273-2-pasha.tatashin@soleen.com>
From:   Anshuman Khandual <anshuman.khandual@arm.com>
Message-ID: <2b3bddd8-e869-a717-b849-d03f30e583c5@arm.com>
Date:   Wed, 2 Feb 2022 11:55:30 +0530
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On 2/1/22 2:02 AM, 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:
> 
> [    2.262821] debug_vm_pgtable: [debug_vm_pgtable         ]: Validating
>                architecture page table helpers
> [    2.276826] ------------[ cut here ]------------
> [    2.280426] kernel BUG at mm/page_table_check.c:162!
> [    2.284118] invalid opcode: 0000 [#1] PREEMPT SMP PTI
> [    2.287787] CPU: 0 PID: 1 Comm: swapper/0 Not tainted
>                5.16.0-11413-g2c271fe77d52 #3
> [    2.293226] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
>                BIOS rel-1.15.0-0-g2dd4b9b3f840-prebuilt.qemu.org
>                04/01/2014
> ...
> 
> 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")
> Cc: stable@vger.kernel.org # 5.9+

Not sure marking stable is necessary here.

> 
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> Reviewed-by: Zi Yan <ziy@nvidia.com>
> Tested-by: Zi Yan <ziy@nvidia.com>
> Acked-by: David Rientjes <rientjes@google.com>

Dont see any problems on arm64. Although it would be great to run this
on all enabled platforms.

Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>

> ---
>  mm/debug_vm_pgtable.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
> index a7ac97c76762..db2abd9e415b 100644
> --- a/mm/debug_vm_pgtable.c
> +++ b/mm/debug_vm_pgtable.c
> @@ -171,6 +171,8 @@ 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)
>