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Fri, 03 Jul 2026 00:42:23 -0700 (PDT) Received: from draig.lan ([185.124.0.114]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-493c63bf7efsm112394725e9.14.2026.07.03.00.42.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 03 Jul 2026 00:42:22 -0700 (PDT) Received: from draig (localhost [IPv6:::1]) by draig.lan (Postfix) with ESMTP id 5A8225F7F7; Fri, 03 Jul 2026 08:42:20 +0100 (BST) From: =?utf-8?Q?Alex_Benn=C3=A9e?= To: Richard Henderson Cc: qemu-devel@nongnu.org, philmd@oss.qualcomm.com, qemu-stable@nongnu.org Subject: Re: [PATCH] accel/tcg: Use TLB_FORCE_SLOW not TLB_MMIO for user-only plugins In-Reply-To: <20260702171057.47998-1-richard.henderson@linaro.org> (Richard Henderson's message of "Thu, 2 Jul 2026 10:10:56 -0700") References: <20260702171057.47998-1-richard.henderson@linaro.org> User-Agent: mu4e 1.14.2; emacs 30.1 Date: Fri, 03 Jul 2026 08:42:20 +0100 Message-ID: <87echksen7.fsf@draig.linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=2a00:1450:4864:20::32d; envelope-from=alex.bennee@linaro.org; helo=mail-wm1-x32d.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 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: qemu development 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 Richard Henderson writes: > In 6d03226b422 we set TLB_MMIO to a non-zero value for user-only > so that we could return a non-zero value from probe_* functions > so that we could force callers like Arm SVE vector moves to use > the slow path rather than direct access. All for the sake of > exposing these accesses to plugins. > > Back then, TLB_FORCE_SLOW did not exist, so TLB_MMIO seemed like > a reasonable solution. However, user-only doesn't really have > MMIO and this has knock-on effects, like forcing Arm SVE first-fault > vector loads to stop. Better to use TLB_FORCE_SLOW as a more exact > exact trigger for plugins. > > Cc: qemu-stable@nongnu.org > Fixes: 6d03226b422 ("plugins: force slow path when plugins instrument mem= ory ops") > Signed-off-by: Richard Henderson Acked-by: Alex Benn=C3=A9e --=20 Alex Benn=C3=A9e Virtualisation Tech Lead @ Linaro