linux-kernel - Re: [PATCH v3 1/4] mm/debug_vm_pgtable: remove pte entry from the page table

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Message-ID: <6e7a364-f252-9622-38c0-d0b7541f87a4@google.com>
Date:   Tue, 25 Jan 2022 22:26:59 -0800 (PST)
From:   David Rientjes <rientjes@...gle.com>
To:     Pasha Tatashin <pasha.tatashin@...een.com>
cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, 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,
        ziy@...dia.com, anshuman.khandual@....com
Subject: Re: [PATCH v3 1/4] mm/debug_vm_pgtable: remove pte entry from the
 page table

On Wed, 26 Jan 2022, 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")
> 
> Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
> Reviewed-by: Zi Yan <ziy@...dia.com>
> Tested-by: Zi Yan <ziy@...dia.com>

Acked-by: David Rientjes <rientjes@...gle.com>

I think we also likely want:

Cc: stable@...r.kernel.org # 5.9+