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([2804:7f0:b401:e1f2:3e7c:3fff:fe7a:e83b]) by smtp.gmail.com with ESMTPSA id y17-20020a170903011100b001d71cbf200esm5972636plc.260.2024.01.22.13.12.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 22 Jan 2024 13:12:41 -0800 (PST) From: Gustavo Romero To: qemu-trivial@nongnu.org, peter.maydell@linaro.org Cc: qemu-devel@nongnu.org, philmd@linaro.org, alex.bennee@linaro.org, richard.henderson@linaro.org, gustavo.romero@linaro.org Subject: [PATCH v2] docs/system/arm/virt.rst: Add note on CPU features off by default Date: Mon, 22 Jan 2024 21:12:15 +0000 Message-Id: <20240122211215.95073-1-gustavo.romero@linaro.org> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 Received-SPF: pass client-ip=2607:f8b0:4864:20::536; envelope-from=gustavo.romero@linaro.org; helo=mail-pg1-x536.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 Add a note on CPU features that are off by default in `virt` machines. Some CPU features will remain off even if a CPU-capable CPU (e.g., `-cpu max`) is selected because they require support in both the CPU itself and in the wider system. Therefore, the user, besides selecting a CPU that supports such features, must also turn on the feature using a machine option. Signed-off-by: Gustavo Romero --- docs/system/arm/virt.rst | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/docs/system/arm/virt.rst b/docs/system/arm/virt.rst index c245c52b7a..1888e31956 100644 --- a/docs/system/arm/virt.rst +++ b/docs/system/arm/virt.rst @@ -69,6 +69,19 @@ Supported guest CPU types: Note that the default is ``cortex-a15``, so for an AArch64 guest you must specify a CPU type. +Also, please note that passing ``max`` CPU (i.e. ``-cpu max``) won't +enable all the CPU features for a given ``virt`` machine. Where a CPU +architectural feature requires support in both the CPU itself and in the +wider system (e.g. the MTE feature), it may not be enabled by default, +but instead requires a machine option to enable it. + +For example, MTE support must be enabled with ``-machine virt,mte=on``, +as well as by selecting an MTE-capable CPU (e.g., ``max``) with the +``-cpu`` option. + +See the machine-specific options below or check them for a given machine +passing ``help``, like: ``-machine virt-9.0,help``. + Graphics output is available, but unlike the x86 PC machine types there is no default display device enabled: you should select one from the Display devices section of "-device help". The recommended option