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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=RVC+g/MypPGtgpKFXu94wOCcPJ3eIBmkEiXHw/lax/gsDseqBbNEtZmJDeS33+zkh wC+Cd92i4lyXqS6rZg9iJMBRJLOEAm+f1YWFMUscBpFSIFDG1QDDxq+6Eoq/SApNkh 1NngORXJi74geLZMY+dO5MZP+ze4M+ooDU/mmax0= Message-ID: <0a466a66-e9a3-4789-a144-8e938df30010@arm.com> Date: Thu, 9 Apr 2026 07:29:30 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] perf/events: Replace READ_ONCE() with standard pgtable accessors To: David Laight Cc: linux-mm@kvack.org, Andrew Morton , David Hildenbrand , David Hildenbrand , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260227062744.2215491-1-anshuman.khandual@arm.com> <1267a6c0-f8e7-4708-96da-4d131b5c6069@arm.com> <20260408134923.3a44a703@pumpkin> Content-Language: en-US From: Anshuman Khandual In-Reply-To: <20260408134923.3a44a703@pumpkin> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 0C47F12000B X-Stat-Signature: wf4yph9zisqc5fkgfskziukz6a87y497 X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1775699977-378598 X-HE-Meta: U2FsdGVkX1/c4GBeLVvIAnbVDUnDTpQNFaeLUYzeu/5Rzq7ZMX1e+N9cC/E7hjJ9NPoiWl1JPy2+AgeA1nxOHRiAcafSZfg0LzfhQi7+HyM/S6WTIVEDmBL0fajp1rCDC2N+2UMtEa2GY0tPaipwY418cw5y5B97XdmeXL3zOTzjVctaidjTCfqeuC+g4X8laedhHmevSwyGsuei3n/Tr601jMv288Oc7Szwr+OYNBZv1k68vh1uQDFzTZ3XnylUVxhipCOSNjsjFSZfezhhRis/VXFIwId4pU7ynbMPAzT6k/idvx2ZnuwKMpE4fbJHoqdfc3Ln/3cxxtdqEXVGQ5DcEqt2byEVHoay61B6bugqZEkGVUKriCYecGYzKoZMN1PGxhHChStCzNCDA41Jhy/zpkpHKIXPSYwCL+r6/eWbPjHlg634ynADkc6iPTzaNbvrd3gUIaaBAfbxwvVflq4R2W6ccfhvvraHYuXO41XYJ2ES3jBOYgfZYzMmtSljrkYUENQvDZi+kHNK1sCw02hxPnrDx2KUovIPPBAFiqa/gkTuAjeSJyl+IXLZsDXaHVG3AiRBBstAnjoCxedRzYBwpFiLsgNLQw6etsQ2OyvouPqMPyTMT1MSy+9k9Gii4VJwNhcX4tZR7L3Hy6E79rqcwiaS5Bqb0kXFyL8AtwiZ1c9r8GqJPwUSZTMwc9vcA9Uh2XMmeC4y0+L4yyMzs/xq3Oyshzc4FuN2dbgX6naNjHmTKYBJ5qkxV1MRvArOXNc8Pl4OFscBFBDe3nxNgyJDYg0ZRHsDta8ojGk85wGIFOpBpEdM7ccTZL9mqmCuiSaI548fl8P3YYAgFS3lA4WaeNPT3r/oT4u6UzvRUp/FcWUgxlBQ1eCbu+Esda0a8X3eBft1noWYdCJj25UxNyuMbkb1vc9KwwUR/JMW1ANq1LWs6As6pKn2XD04qj/PafpLDaYImwU3vbd2Cxl 5s1KiDjx VD06dTtW3VBRGckFy1DG/dZpYBCi8VEiCH7H5DkwLrS9cwWrO0mPy4K3KWw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 08/04/26 6:19 PM, David Laight wrote: > On Tue, 7 Apr 2026 08:58:46 +0530 > Anshuman Khandual 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.