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

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Message-ID: <20250612145808.GA12912@willie-the-truck>
Date: Thu, 12 Jun 2025 15:58:08 +0100
From: Will Deacon <will@...nel.org>
To: Anshuman Khandual <anshuman.khandual@....com>
Cc: linux-arm-kernel@...ts.infradead.org, stable@...r.kernel.org,
	Catalin Marinas <catalin.marinas@....com>,
	Ryan Roberts <ryan.roberts@....com>, linux-kernel@...r.kernel.org,
	Dev Jain <dev.jain@....com>
Subject: Re: [PATCH] arm64/ptdump: Ensure memory hotplug is prevented during
 ptdump_check_wx()

On Mon, Jun 09, 2025 at 05:12:14AM +0100, 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().

How do other architectures (e.g. x86) handle this? I don't see any usage
of {get,put}_online_mems() over there. Should this be moved into the core
code?

Will