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Mon, 17 Nov 2025 17:45:57 -0800 (PST) Message-ID: <0f6fe0c6-7c11-4f16-bed4-db4de675b002@gmail.com> Date: Tue, 18 Nov 2025 07:15:50 +0530 Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4] arm64: errata: Work around AmpereOne's erratum AC04_CPU_23 To: D Scott Phillips , Catalin Marinas , James Clark , James Morse , Joey Gouly , Kevin Brodsky , Marc Zyngier , Mark Brown , Mark Rutland , Oliver Upton , "Rob Herring (Arm)" , Shameer Kolothum , Shiqi Liu , Will Deacon , Yicong Yang , kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <20250513184514.2678288-1-scott@os.amperecomputing.com> <456bba04-07b7-4c27-96fc-9bf226b12fd9@gmail.com> <86bjl0o9yd.fsf@scott-ph-mail.amperecomputing.com> Content-Language: en-US From: Jaikiran Pai In-Reply-To: <86bjl0o9yd.fsf@scott-ph-mail.amperecomputing.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 17/11/25 10:47 pm, D Scott Phillips wrote: > Jaikiran Pai writes: > >> Hello Scott, >> >> On 14/05/25 12:15 am, D Scott Phillips wrote: >>> On AmpereOne AC04, updates to HCR_EL2 can rarely corrupt simultaneous >>> translations for data addresses initiated by load/store instructions. >>> Only instruction initiated translations are vulnerable, not translations >>> from prefetches for example. A DSB before the store to HCR_EL2 is >>> sufficient to prevent older instructions from hitting the window for >>> corruption, and an ISB after is sufficient to prevent younger >>> instructions from hitting the window for corruption. >> I see that this patch enables the workaround only for AmpereOne AC04 >> systems. Do you happen to know if the underlying issue for which this >> patch was introduced, impacts (or can impact) AmpereOne AC03 systems too: > Hi Jaikiran, this issue impacts ac04 only, it is not present on ac03. Thank you Scott for the quick confirmation. We have been investigating an issue on AC03 (running Oracle Linux as a VM) where some memory writes (stores) are lost especially when the OS appears to have accumulated high buf/cache usage (monitored through free -h). That investigation, backed by a trivial C reproducer, is still ongoing and we are trying to understand what could be causing it. The issue description here made us curious whether it's the same issue we are running into and since this patch wasn't applied on AC03, we decided to check once. While at it, if you have any inputs (tools/commands) that you typically use to narrow down such issues, I would be happy to experiment with if feasible. Right now we are focusing on the kernel itself and checking which specific kernel versions can reproduce it. We have been able to reproduce it consistently on 5.15.x and 5.16.x and we plan to try it with other kernel versions all the way upto 6.12. That should tell us if the issue we are encountering has already been addressed in any specific kernel version. Given that you noted this patch isn't relevant for AC03, I don't plan to further reply-all to this PATCH discussion, but if you would like me to keep you updated with this investigation (I would love to get some inputs and provide updates as we go along) then please let me know and I will communicate with you over your email (or any other relevant forum you suggest). Thank you again for the quick response. -Jaikiran