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Tue, 06 Feb 2024 16:31:47 -0800 (PST) Message-ID: Date: Wed, 7 Feb 2024 10:31:42 +1000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/6] linux-user/aarch64: Extend PR_SET_TAGGED_ADDR_CTRL for FEAT_MTE3 Content-Language: en-US To: Peter Maydell Cc: qemu-devel@nongnu.org, qemu-arm@nongnu.org, gustavo.romero@linaro.org References: <20240206030527.169147-1-richard.henderson@linaro.org> <20240206030527.169147-2-richard.henderson@linaro.org> From: Richard Henderson In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2607:f8b0:4864:20::434; envelope-from=richard.henderson@linaro.org; helo=mail-pf1-x434.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 2/7/24 00:23, Peter Maydell wrote: > On Tue, 6 Feb 2024 at 03:06, Richard Henderson > wrote: >> >> When MTE3 is supported, the kernel maps >> PR_MTE_TCF_ASYNC | PR_MTE_TCF_SYNC >> to >> MTE_CTRL_TCF_ASYMM >> and from there to >> SCTLR_EL1.TCF0 = 3 > > This depends on the setting of > /sys/devices/system/cpu/cpu/mte_tcf_preferred : > I think you only get asymm here if the sysadmin has set > mte_tcf_preferred to 'asymm'; the default is 'async'. Hmm, I missed that somewhere in the rat's nest. I suspect this is over-engineered, such that no one will understand how to use it. > For QEMU's implementation, are there any particular > performance differences between sync, async and asymm ? I doubt it. Getting to the error path at all is the bulk of the work. I think "performance" in this case would be highly test-case-centric. Does the test "perform better" with async, which would allow the entire vector operation to finish in one go? I suspect that for debugging purposes, sync is always preferred. That might be the best setting for qemu. r~