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b=AK/o8eNsta406tALZ4n9LY9LZcOKGvZzHbQFlv4LP5s4xN7btezfxtDaU9z81nya+ l6U8c5hPVqwXmGK/Kl0DYNG4ENW9dbQNIkJwlLwoiRsvbF2S7+CCFUKopJXF78x2wp qtg8qNMIMIr8JhD+3m3EU4wdBXE1Vdh8nuk5QpIwFq+AJ/w0/372Fan5CtjG06xRDO cZFRNtt/b06Dt6qADOU/M9gHizfEDHokFdaBR03wKLBw/+ZcKTW/5ZG0aWDVpccajh NHNe4gIQm7cJHXhzEGDMJjNRiYJyXS/umqRLIBpjKwnB2O4sntJSe1exsXm+zqiRTL T9FweJd2d5C/w== Message-ID: <0deef591-d82a-4034-9514-abde0e73e5e5@kernel.org> Date: Wed, 16 Sep 2026 15:34:24 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 02/17] arm64/mm: Convert READ_ONCE() as pmdp_get() while accessing PMD From: "David Hildenbrand (Arm)" To: Anshuman Khandual , linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org Cc: Catalin Marinas , Will Deacon , Ryan Roberts , Mark Rutland , Lorenzo Stoakes , Andrew Morton , Mike Rapoport , Linu Cherian , linux-kernel@vger.kernel.org, Mark Rtland , linx-arm-kernel@lists.infradead.org, linx-kernel@vger.kernel.org, kasan-dev@googlegrops.com References: <20260729122452.3797443-1-anshuman.khandual@arm.com> <20260729122452.3797443-3-anshuman.khandual@arm.com> Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: F19F5140012 X-Stat-Signature: hzpi5khzaj3gkwus75qecfc6z4q3fq5r X-Rspamd-Server: rspam01 X-HE-Tag: 1789565669-782254 X-HE-Meta: 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 f0gQ6J6o MjdKQtA1vhHWxKy6qDMmW3EVaJmfKbgt8ZNfX/5k2XNoYvL3P1RYy/1D/q7PFRh2cfwYukf0ZGswTTkZJFM6GpXVOCiMG0LZe3f3lDkELPyAqOfoXxxaDEDeIX4/yOjWRoEluRQfpPD2a3AXptELQ0qsVGj/vTL5Nhq4GQD1KIgcRXlGXwnPs/rmUlMGCANXES4OtLwsAZ5pqnwrPPd3Hv89WZ1URNwzI+TBQjTA79yBQ3Mvcd8I99YzFZ4dAgUslVJswcpHiMihiViUP1UVYC5E4tKgO6o3VNm8dpNVuBSy1RmURYNSeJKeBiLjOlxGphLVqVigrPMriQ0g= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/16/26 15:32, David Hildenbrand (Arm) wrote: > On 7/29/26 14:24, Anshuman Khandual wrote: >> Convert all READ_ONCE() based PMD accesses as pmdp_get() instead which will >> support both D64 and D128 translation regime going forward. That is because >> READ_ONCE() would need 128 bit single copy atomic guarantees, while reading >> 128 bit page table entries which is currently not supported on arm64. Build >> fails for READ_ONCE() while accessing beyond 64 bits. >> >> Load Pair/Store Pair (ldp/stp) are only single copy atomic if FEAT_LSE128 >> is supported (which is required when FEAT_D128 is supported). Currently 128 >> bit pgtables is a compile time decision - so we could have chosen to extend >> READ_ONCE()/WRITE_ONCE() to allow 128 bit for this configuration. But then >> it's a general purpose API and we were concerned that other users might >> eventually creep in that expect 128 and then fail to compile in the other >> configs. >> >> But worse, we are considering eventually making D128 a boot time option, at >> which point we'd have to make READ_ONCE() always allow 128 bit at compile >> time but then it might silently tear at runtime. >> >> So our preference is to standardize on these existing helpers, which we can >> override in arm64 to give the 128 bit single copy guarantee when required. >> > > Best to mention here that no functional change is expect because the common-cde > pmdp_get() etc helpers do exactly that. > > Reviewed-by: David Hildenbrand (Arm) > Whops, accidentally stumbled into v1 in my inbox after starting to look at v2 :D -- Cheers, David