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Date: Thu, 9 Apr 2026 07:29:30 +0530
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Subject: Re: [PATCH] perf/events: Replace READ_ONCE() with standard pgtable
 accessors
To: David Laight <david.laight.linux@gmail.com>
Cc: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
 David Hildenbrand <david@redhat.com>, David Hildenbrand <david@kernel.org>,
 Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>,
 Arnaldo Carvalho de Melo <acme@kernel.org>,
 Namhyung Kim <namhyung@kernel.org>, linux-perf-users@vger.kernel.org,
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References: <20260227062744.2215491-1-anshuman.khandual@arm.com>
 <1267a6c0-f8e7-4708-96da-4d131b5c6069@arm.com>
 <20260408134923.3a44a703@pumpkin>
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From: Anshuman Khandual <anshuman.khandual@arm.com>
In-Reply-To: <20260408134923.3a44a703@pumpkin>
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On 08/04/26 6:19 PM, David Laight wrote:
> On Tue, 7 Apr 2026 08:58:46 +0530
> Anshuman Khandual <anshuman.khandual@arm.com> wrote:
> 
>> On 27/02/26 11:57 AM, Anshuman Khandual wrote:
>>> Replace raw READ_ONCE() dereferences of pgtable entries with corresponding
>>> standard page table accessors pxdp_get() in perf_get_pgtable_size(). These
>>> accessors default to READ_ONCE() on platforms that don't override them. So
>>> there is no functional change on such platforms.
>>>
>>> However arm64 platform is being extended to support 128 bit page tables via
>>> a new architecture feature i.e FEAT_D128 in which case READ_ONCE() will not
>>> provide required single copy atomic access for 128 bit page table entries.
>>> Although pxdp_get() accessors can later be overridden on arm64 platform to
>>> extend required single copy atomicity support on 128 bit entries.
>>
> 
> Did you consider enhancing READ_ONCE() to support 128bit accesses on arm64?

Yes although it does not really meet all requirements for 128 bit page table access.