linux-kernel - Re: [PATCH] arm64/ptdump: Ensure memory hotplug is prevented during ptdump_check

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Message-ID: <b437b07b-bc62-421b-9a5f-5fa414fc8b5f@arm.com>
Date: Mon, 9 Jun 2025 10:39:54 +0530
From: Dev Jain <dev.jain@....com>
To: Anshuman Khandual <anshuman.khandual@....com>,
 linux-arm-kernel@...ts.infradead.org
Cc: stable@...r.kernel.org, Catalin Marinas <catalin.marinas@....com>,
 Will Deacon <will@...nel.org>, Ryan Roberts <ryan.roberts@....com>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64/ptdump: Ensure memory hotplug is prevented during
 ptdump_check_wx()


On 09/06/25 9:42 am, Anshuman Khandual wrote:
> The arm64 page table dump code can race with concurrent modification of the
> kernel page tables. When a leaf entries are modified concurrently, the dump
> code may log stale or inconsistent information for a VA range, but this is
> otherwise not harmful.
>
> When intermediate levels of table are freed, the dump code will continue to
> use memory which has been freed and potentially reallocated for another
> purpose. In such cases, the dump code may dereference bogus addresses,
> leading to a number of potential problems.
>
> This problem was fixed for ptdump_show() earlier via commit 'bf2b59f60ee1
> ("arm64/mm: Hold memory hotplug lock while walking for kernel page table
> dump")' but a same was missed for ptdump_check_wx() which faced the race
> condition as well. Let's just take the memory hotplug lock while executing
> ptdump_check_wx().
>
> Cc: stable@...r.kernel.org
> Fixes: bbd6ec605c0f ("arm64/mm: Enable memory hot remove")
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Ryan Roberts <ryan.roberts@....com>
> Cc: linux-arm-kernel@...ts.infradead.org
> Cc: linux-kernel@...r.kernel.org
> Reported-by: Dev Jain <dev.jain@....com>
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> ---

LGTM

Reviewed-by: Dev Jain <dev.jain@....com>