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Mon, 12 Oct 2026 06:48:48 -0700 (PDT) From: =?UTF-8?q?Alex=20Benn=C3=A9e?= To: qemu-devel@nongnu.org Cc: =?UTF-8?q?Alex=20Benn=C3=A9e?= , Paolo Bonzini , Richard Henderson , =?UTF-8?q?Philippe=20Mathieu-Daud=C3=A9?= , Peter Maydell , qemu-arm@nongnu.org (open list:ARM TCG CPUs) Subject: [RFC PATCH] target/arm: hold bql when SEV sets the event_register Date: Mon, 12 Oct 2026 14:48:40 +0100 Message-ID: <20261012134840.1051969-1-alex.bennee@linaro.org> X-Mailer: git-send-email 2.47.3 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists1p.gnu.org; Received-SPF: pass client-ip=2a00:1450:4864:20::334; envelope-from=alex.bennee@linaro.org; helo=mail-wm1-x334.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+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @linaro.org) X-ZM-MESSAGEID: 1791812976688158500 There is a race in qemu_process_cpu_events and sleeping on halt_cond where we can miss the setting of the event_register which would cause arm_cpu_has_work to report we shouldn't sleep. As by definition the bql has to be held when we go to sleep against halt_cond guard the kicking of the cpus by the SEV helper with the BQL to ensure things are properly serialised. The other places that set event_register are fine as they are either in the same vCPU context or are already serialised by the BQL. Also use qemu_cond_wait_bql like the other halt_cond users. Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/4660 Signed-off-by: Alex Benn=C3=A9e Reviewed-by: Paolo Bonzini --- system/cpus.c | 2 +- target/arm/tcg/op_helper.c | 3 +++ 2 files changed, 4 insertions(+), 1 deletion(-) diff --git a/system/cpus.c b/system/cpus.c index e11a5aab6a6..985732217fb 100644 --- a/system/cpus.c +++ b/system/cpus.c @@ -412,7 +412,7 @@ void qemu_process_cpu_events(CPUState *cpu) slept =3D true; qemu_plugin_vcpu_idle_cb(cpu); } - qemu_cond_wait(cpu->halt_cond, &bql); + qemu_cond_wait_bql(cpu->halt_cond); } if (slept) { qemu_plugin_vcpu_resume_cb(cpu); diff --git a/target/arm/tcg/op_helper.c b/target/arm/tcg/op_helper.c index af56eff9f18..7c1fdab79d7 100644 --- a/target/arm/tcg/op_helper.c +++ b/target/arm/tcg/op_helper.c @@ -471,6 +471,9 @@ void HELPER(wfit)(CPUARMState *env, uint32_t rd) void HELPER(sev)(CPUARMState *env) { CPUState *cs =3D env_cpu(env); + + BQL_LOCK_GUARD(); + CPU_FOREACH(cs) { ARMCPU *target_cpu =3D ARM_CPU(cs); target_cpu->env.event_register =3D true; --=20 2.47.3