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Mon, 08 Sep 2025 03:13:08 -0700 (PDT) X-Google-Smtp-Source: AGHT+IETPYIPWARpMny9jmQtqFuA7IPClj38ZHOG5z7M2vc4aWwgns8nIwsGlIiGgLvABmVep2ujJw== X-Received: by 2002:a05:6000:1acd:b0:3e5:50:e070 with SMTP id ffacd0b85a97d-3e64c789650mr4848477f8f.50.1757326387757; Mon, 08 Sep 2025 03:13:07 -0700 (PDT) From: Paolo Bonzini To: qemu-devel@nongnu.org Cc: Richard Henderson , =?UTF-8?q?Philippe=20Mathieu-Daud=C3=A9?= , Peter Xu , Igor Mammedov Subject: [PATCH 10/19] accel: use atomic accesses for exit_request Date: Mon, 8 Sep 2025 12:12:32 +0200 Message-ID: <20250908101241.2110068-11-pbonzini@redhat.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20250908101241.2110068-1-pbonzini@redhat.com> References: <20250908101241.2110068-1-pbonzini@redhat.com> 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=lists.gnu.org; Received-SPF: pass client-ip=170.10.129.124; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=-1, RCVD_IN_MSPIKE_WL=-0.01, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_PASS=-0.001, T_SPF_HELO_TEMPERROR=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+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1757326594972116600 CPU threads write exit_request as a "note to self" that they need to go out to a slow path. This write happens out of the BQL and can be a data race with another threads' cpu_exit(); use atomic accesses consistently. While at it, change the source argument from int ("1") to bool ("true"). Reviewed-by: Richard Henderson Reviewed-by: Philippe Mathieu-Daud=C3=A9 Reviewed-by: Peter Xu Reviewed-by: Igor Mammedov Signed-off-by: Paolo Bonzini --- include/hw/core/cpu.h | 9 +++++++++ accel/kvm/kvm-all.c | 2 +- accel/tcg/tcg-accel-ops-mttcg.c | 2 +- accel/tcg/tcg-accel-ops-rr.c | 4 ++-- hw/ppc/spapr_hcall.c | 6 +++--- target/i386/kvm/kvm.c | 6 +++--- target/i386/nvmm/nvmm-accel-ops.c | 2 +- target/i386/nvmm/nvmm-all.c | 2 +- target/i386/whpx/whpx-all.c | 6 +++--- 9 files changed, 24 insertions(+), 15 deletions(-) diff --git a/include/hw/core/cpu.h b/include/hw/core/cpu.h index 8b57bcd92c9..338757e5254 100644 --- a/include/hw/core/cpu.h +++ b/include/hw/core/cpu.h @@ -422,6 +422,15 @@ struct qemu_work_item; * valid under cpu_list_lock. * @created: Indicates whether the CPU thread has been successfully create= d. * @halt_cond: condition variable sleeping threads can wait on. + * @exit_request: Another thread requests the CPU to call qemu_wait_io_eve= nt(). + * Should be read only by CPU thread with load-acquire, to synchronize w= ith + * other threads' store-release operation. + * + * In some cases, accelerator-specific code will write exit_request from + * within the same thread, to "bump" the effect of qemu_cpu_kick() to + * the one provided by cpu_exit(), especially when processing interrupt + * flags. In this case, the write and read happen in the same thread + * and the write therefore can use qemu_atomic_set(). * @interrupt_request: Indicates a pending interrupt request. * Only used by system emulation. * @halted: Nonzero if the CPU is in suspended state. diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c index bd9e5e3886d..e4167d94b4f 100644 --- a/accel/kvm/kvm-all.c +++ b/accel/kvm/kvm-all.c @@ -3730,7 +3730,7 @@ int kvm_on_sigbus_vcpu(CPUState *cpu, int code, void = *addr) have_sigbus_pending =3D true; pending_sigbus_addr =3D addr; pending_sigbus_code =3D code; - qatomic_set(&cpu->exit_request, 1); + qatomic_set(&cpu->exit_request, true); return 0; #else return 1; diff --git a/accel/tcg/tcg-accel-ops-mttcg.c b/accel/tcg/tcg-accel-ops-mttc= g.c index 337b993d3da..b12b7a36b5d 100644 --- a/accel/tcg/tcg-accel-ops-mttcg.c +++ b/accel/tcg/tcg-accel-ops-mttcg.c @@ -85,7 +85,7 @@ static void *mttcg_cpu_thread_fn(void *arg) qemu_guest_random_seed_thread_part2(cpu->random_seed); =20 /* process any pending work */ - cpu->exit_request =3D 1; + qatomic_set(&cpu->exit_request, true); =20 do { if (cpu_can_run(cpu)) { diff --git a/accel/tcg/tcg-accel-ops-rr.c b/accel/tcg/tcg-accel-ops-rr.c index e8b0e370a8d..d13e0d8b44d 100644 --- a/accel/tcg/tcg-accel-ops-rr.c +++ b/accel/tcg/tcg-accel-ops-rr.c @@ -212,7 +212,7 @@ static void *rr_cpu_thread_fn(void *arg) cpu =3D first_cpu; =20 /* process any pending work */ - cpu->exit_request =3D 1; + qatomic_set(&cpu->exit_request, true); =20 while (1) { /* Only used for icount_enabled() */ @@ -293,7 +293,7 @@ static void *rr_cpu_thread_fn(void *arg) /* Does not need a memory barrier because a spurious wakeup is oka= y. */ qatomic_set(&rr_current_cpu, NULL); =20 - if (cpu && cpu->exit_request) { + if (cpu && qatomic_read(&cpu->exit_request)) { qatomic_set_mb(&cpu->exit_request, 0); } =20 diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c index 1e936f35e44..51875e32a09 100644 --- a/hw/ppc/spapr_hcall.c +++ b/hw/ppc/spapr_hcall.c @@ -509,7 +509,7 @@ static target_ulong h_cede(PowerPCCPU *cpu, SpaprMachin= eState *spapr, if (!cpu_has_work(cs)) { cs->halted =3D 1; cs->exception_index =3D EXCP_HLT; - cs->exit_request =3D 1; + qatomic_set(&cs->exit_request, true); ppc_maybe_interrupt(env); } =20 @@ -531,7 +531,7 @@ static target_ulong h_confer_self(PowerPCCPU *cpu) } cs->halted =3D 1; cs->exception_index =3D EXCP_HALTED; - cs->exit_request =3D 1; + qatomic_set(&cs->exit_request, true); ppc_maybe_interrupt(&cpu->env); =20 return H_SUCCESS; @@ -624,7 +624,7 @@ static target_ulong h_confer(PowerPCCPU *cpu, SpaprMach= ineState *spapr, } =20 cs->exception_index =3D EXCP_YIELD; - cs->exit_request =3D 1; + qatomic_set(&cs->exit_request, true); cpu_loop_exit(cs); =20 return H_SUCCESS; diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c index 8420c4090ef..34e74f24470 100644 --- a/target/i386/kvm/kvm.c +++ b/target/i386/kvm/kvm.c @@ -5486,10 +5486,10 @@ void kvm_arch_pre_run(CPUState *cpu, struct kvm_run= *run) if (cpu_test_interrupt(cpu, CPU_INTERRUPT_INIT | CPU_INTERRUPT_TPR)) { if (cpu_test_interrupt(cpu, CPU_INTERRUPT_INIT) && !(env->hflags & HF_SMM_MASK)) { - qatomic_set(&cpu->exit_request, 1); + qatomic_set(&cpu->exit_request, true); } if (cpu_test_interrupt(cpu, CPU_INTERRUPT_TPR)) { - qatomic_set(&cpu->exit_request, 1); + qatomic_set(&cpu->exit_request, true); } } =20 @@ -5604,7 +5604,7 @@ int kvm_arch_process_async_events(CPUState *cs) if (env->exception_nr =3D=3D EXCP08_DBLE) { /* this means triple fault */ qemu_system_reset_request(SHUTDOWN_CAUSE_GUEST_RESET); - cs->exit_request =3D 1; + qatomic_set(&cs->exit_request, true); return 0; } kvm_queue_exception(env, EXCP12_MCHK, 0, 0); diff --git a/target/i386/nvmm/nvmm-accel-ops.c b/target/i386/nvmm/nvmm-acce= l-ops.c index 3799260bbde..86869f133e9 100644 --- a/target/i386/nvmm/nvmm-accel-ops.c +++ b/target/i386/nvmm/nvmm-accel-ops.c @@ -77,7 +77,7 @@ static void nvmm_start_vcpu_thread(CPUState *cpu) */ static void nvmm_kick_vcpu_thread(CPUState *cpu) { - cpu->exit_request =3D 1; + qatomic_set(&cpu->exit_request, true); cpus_kick_thread(cpu); } =20 diff --git a/target/i386/nvmm/nvmm-all.c b/target/i386/nvmm/nvmm-all.c index 10bd51d9b59..7e36c42fbb4 100644 --- a/target/i386/nvmm/nvmm-all.c +++ b/target/i386/nvmm/nvmm-all.c @@ -414,7 +414,7 @@ nvmm_vcpu_pre_run(CPUState *cpu) * or commit pending TPR access. */ if (cpu_test_interrupt(cpu, CPU_INTERRUPT_INIT | CPU_INTERRUPT_TPR)) { - cpu->exit_request =3D 1; + qatomic_set(&cpu->exit_request, true); } =20 if (!has_event && cpu_test_interrupt(cpu, CPU_INTERRUPT_NMI)) { diff --git a/target/i386/whpx/whpx-all.c b/target/i386/whpx/whpx-all.c index 2106c29c3a0..00fb7e23100 100644 --- a/target/i386/whpx/whpx-all.c +++ b/target/i386/whpx/whpx-all.c @@ -1489,10 +1489,10 @@ static void whpx_vcpu_pre_run(CPUState *cpu) if (cpu_test_interrupt(cpu, CPU_INTERRUPT_INIT | CPU_INTERRUPT_TPR)) { if (cpu_test_interrupt(cpu, CPU_INTERRUPT_INIT) && !(env->hflags & HF_SMM_MASK)) { - cpu->exit_request =3D 1; + qatomic_set(&cpu->exit_request, true); } if (cpu_test_interrupt(cpu, CPU_INTERRUPT_TPR)) { - cpu->exit_request =3D 1; + qatomic_set(&cpu->exit_request, true); } } =20 @@ -1539,7 +1539,7 @@ static void whpx_vcpu_pre_run(CPUState *cpu) if (tpr !=3D vcpu->tpr) { vcpu->tpr =3D tpr; reg_values[reg_count].Reg64 =3D tpr; - cpu->exit_request =3D 1; + qatomic_set(&cpu->exit_request, true); reg_names[reg_count] =3D WHvX64RegisterCr8; reg_count +=3D 1; } --=20 2.51.0