From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marc Zyngier Subject: Re: [PATCH v3 3/5] KVM: arm/arm64: Support arch timers with a userspace gic Date: Thu, 6 Apr 2017 09:25:13 +0100 Message-ID: References: <20170405092815.22503-1-cdall@linaro.org> <20170405092815.22503-4-cdall@linaro.org> <358febe2-eb7b-93fa-fa95-ca618443f242@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org, Peter Maydell , Pekka Enberg , Christoffer Dall To: Alexander Graf , Christoffer Dall , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org Return-path: Received: from foss.arm.com ([217.140.101.70]:38884 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752692AbdDFIZU (ORCPT ); Thu, 6 Apr 2017 04:25:20 -0400 In-Reply-To: <358febe2-eb7b-93fa-fa95-ca618443f242@suse.de> Sender: kvm-owner@vger.kernel.org List-ID: On 06/04/17 09:16, Alexander Graf wrote: > > > On 05.04.17 11:28, Christoffer Dall wrote: >> From: Alexander Graf >> >> If you're running with a userspace gic or other interrupt constroller >> (that is no vgic in the kernel), then you have so far not been able to >> use the architected timers, because the output of the architected >> timers, which are driven inside the kernel, was a kernel-only construct >> between the arch timer code and the vgic. >> >> This patch implements the new KVM_CAP_ARM_USER_IRQ feature, where we use a >> side channel on the kvm_run structure, run->s.regs.device_irq_level, to >> always notify userspace of the timer output levels when using a userspace >> irqchip. >> >> This works by ensureing that before we enter the guest, if the timer >> output level has changed compared to what we last told userspace, we >> don't enter the guest, but instead return to userspace to notify it of >> the new level. If we are exiting, because of an MMIO for example, and >> the level changed at the same time, the value is also updated and >> userspace can sample the line as it needs. This is nicely achieved >> simply always updating the timer_irq_level field after the main run >> loop. >> >> Note that the kvm_timer_update_irq trace event is changed to show the >> host IRQ number for the timer instead of the guest IRQ number, because >> the kernel no longer know which IRQ userspace wires up the timer signal >> to. >> >> Also note that this patch implements all required functionality but does >> not yet advertise the capability. >> >> Signed-off-by: Alexander Graf >> Signed-off-by: Christoffer Dall >> --- >> arch/arm/kvm/arm.c | 18 +++---- >> include/kvm/arm_arch_timer.h | 2 + >> virt/kvm/arm/arch_timer.c | 122 +++++++++++++++++++++++++++++++++++-------- >> 3 files changed, 110 insertions(+), 32 deletions(-) >> >> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c >> index 7fa4898..efb16e5 100644 >> --- a/arch/arm/kvm/arm.c >> +++ b/arch/arm/kvm/arm.c >> @@ -515,13 +515,7 @@ static int kvm_vcpu_first_run_init(struct kvm_vcpu *vcpu) >> return ret; >> } >> >> - /* >> - * Enable the arch timers only if we have an in-kernel VGIC >> - * and it has been properly initialized, since we cannot handle >> - * interrupts from the virtual timer with a userspace gic. >> - */ >> - if (irqchip_in_kernel(kvm) && vgic_initialized(kvm)) >> - ret = kvm_timer_enable(vcpu); >> + ret = kvm_timer_enable(vcpu); >> >> return ret; >> } >> @@ -640,9 +634,12 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run) >> local_irq_disable(); >> >> /* >> - * Re-check atomic conditions >> + * If we have a singal pending, or need to notify a userspace >> + * irqchip about timer level changes, then we exit (and update >> + * the timer level state in kvm_timer_update_run below). >> */ >> - if (signal_pending(current)) { >> + if (signal_pending(current) || >> + kvm_timer_should_notify_user(vcpu)) { >> ret = -EINTR; >> run->exit_reason = KVM_EXIT_INTR; >> } >> @@ -714,6 +711,9 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run) >> ret = handle_exit(vcpu, run, ret); >> } >> >> + /* Tell userspace about in-kernel device output levels */ >> + kvm_timer_update_run(vcpu); >> + >> if (vcpu->sigset_active) >> sigprocmask(SIG_SETMASK, &sigsaved, NULL); >> return ret; >> diff --git a/include/kvm/arm_arch_timer.h b/include/kvm/arm_arch_timer.h >> index fe797d6..295584f 100644 >> --- a/include/kvm/arm_arch_timer.h >> +++ b/include/kvm/arm_arch_timer.h >> @@ -63,6 +63,8 @@ int kvm_timer_vcpu_reset(struct kvm_vcpu *vcpu, >> void kvm_timer_vcpu_init(struct kvm_vcpu *vcpu); >> void kvm_timer_flush_hwstate(struct kvm_vcpu *vcpu); >> void kvm_timer_sync_hwstate(struct kvm_vcpu *vcpu); >> +bool kvm_timer_should_notify_user(struct kvm_vcpu *vcpu); >> +void kvm_timer_update_run(struct kvm_vcpu *vcpu); >> void kvm_timer_vcpu_terminate(struct kvm_vcpu *vcpu); >> >> u64 kvm_arm_timer_get_reg(struct kvm_vcpu *, u64 regid); >> diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c >> index 363f0d2..5dc2167 100644 >> --- a/virt/kvm/arm/arch_timer.c >> +++ b/virt/kvm/arm/arch_timer.c >> @@ -184,6 +184,27 @@ bool kvm_timer_should_fire(struct arch_timer_context *timer_ctx) >> return cval <= now; >> } >> >> +/* >> + * Reflect the timer output level into the kvm_run structure >> + */ >> +void kvm_timer_update_run(struct kvm_vcpu *vcpu) >> +{ >> + struct arch_timer_context *vtimer = vcpu_vtimer(vcpu); >> + struct arch_timer_context *ptimer = vcpu_ptimer(vcpu); >> + struct kvm_sync_regs *regs = &vcpu->run->s.regs; >> + >> + if (likely(irqchip_in_kernel(vcpu->kvm))) >> + return; >> + >> + /* Populate the device bitmap with the timer states */ >> + regs->device_irq_level &= ~(KVM_ARM_DEV_EL1_VTIMER | >> + KVM_ARM_DEV_EL1_PTIMER); >> + if (vtimer->irq.level) >> + regs->device_irq_level |= KVM_ARM_DEV_EL1_VTIMER; >> + if (ptimer->irq.level) >> + regs->device_irq_level |= KVM_ARM_DEV_EL1_PTIMER; >> +} >> + >> static void kvm_timer_update_irq(struct kvm_vcpu *vcpu, bool new_level, >> struct arch_timer_context *timer_ctx) >> { >> @@ -194,9 +215,12 @@ static void kvm_timer_update_irq(struct kvm_vcpu *vcpu, bool new_level, >> trace_kvm_timer_update_irq(vcpu->vcpu_id, timer_ctx->irq.irq, >> timer_ctx->irq.level); >> >> - ret = kvm_vgic_inject_irq(vcpu->kvm, vcpu->vcpu_id, timer_ctx->irq.irq, >> - timer_ctx->irq.level); >> - WARN_ON(ret); >> + if (likely(irqchip_in_kernel(vcpu->kvm))) { >> + ret = kvm_vgic_inject_irq(vcpu->kvm, vcpu->vcpu_id, >> + timer_ctx->irq.irq, >> + timer_ctx->irq.level); >> + WARN_ON(ret); >> + } >> } >> >> /* >> @@ -215,7 +239,7 @@ static void kvm_timer_update_state(struct kvm_vcpu *vcpu) >> * because the guest would never see the interrupt. Instead wait >> * until we call this function from kvm_timer_flush_hwstate. >> */ >> - if (!timer->enabled) >> + if (unlikely(!timer->enabled)) >> return; >> >> if (kvm_timer_should_fire(vtimer) != vtimer->irq.level) >> @@ -282,28 +306,12 @@ void kvm_timer_unschedule(struct kvm_vcpu *vcpu) >> timer_disarm(timer); >> } >> >> -/** >> - * kvm_timer_flush_hwstate - prepare to move the virt timer to the cpu >> - * @vcpu: The vcpu pointer >> - * >> - * Check if the virtual timer has expired while we were running in the host, >> - * and inject an interrupt if that was the case. >> - */ >> -void kvm_timer_flush_hwstate(struct kvm_vcpu *vcpu) >> +static void kvm_timer_flush_hwstate_vgic(struct kvm_vcpu *vcpu) >> { >> - struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu; >> struct arch_timer_context *vtimer = vcpu_vtimer(vcpu); >> bool phys_active; >> int ret; >> >> - if (unlikely(!timer->enabled)) >> - return; >> - >> - kvm_timer_update_state(vcpu); >> - >> - /* Set the background timer for the physical timer emulation. */ >> - kvm_timer_emulate(vcpu, vcpu_ptimer(vcpu)); >> - >> /* >> * If we enter the guest with the virtual input level to the VGIC >> * asserted, then we have already told the VGIC what we need to, and >> @@ -355,11 +363,72 @@ void kvm_timer_flush_hwstate(struct kvm_vcpu *vcpu) >> vtimer->active_cleared_last = !phys_active; >> } >> >> +bool kvm_timer_should_notify_user(struct kvm_vcpu *vcpu) >> +{ >> + struct arch_timer_context *vtimer = vcpu_vtimer(vcpu); >> + struct arch_timer_context *ptimer = vcpu_ptimer(vcpu); >> + struct kvm_sync_regs *sregs = &vcpu->run->s.regs; >> + bool vlevel, plevel; >> + >> + if (likely(irqchip_in_kernel(vcpu->kvm))) >> + return false; >> + >> + vlevel = sregs->device_irq_level & KVM_ARM_DEV_EL1_VTIMER; >> + plevel = sregs->device_irq_level & KVM_ARM_DEV_EL1_PTIMER; >> + >> + return vtimer->irq.level != vlevel || >> + ptimer->irq.level != plevel; >> +} >> + >> +static void kvm_timer_flush_hwstate_user(struct kvm_vcpu *vcpu) >> +{ >> + struct arch_timer_context *vtimer = vcpu_vtimer(vcpu); >> + >> + /* >> + * To prevent continuously exiting from the guest, we mask the >> + * physical interrupt such that the guest can make forward progress. >> + * Once we detect the output level being deasserted, we unmask the >> + * interrupt again so that we exit from the guest when the timer >> + * fires. >> + */ >> + if (vtimer->irq.level) >> + disable_percpu_irq(host_vtimer_irq); >> + else >> + enable_percpu_irq(host_vtimer_irq, 0); >> +} >> + >> +/** >> + * kvm_timer_flush_hwstate - prepare timers before running the vcpu >> + * @vcpu: The vcpu pointer >> + * >> + * Check if the virtual timer has expired while we were running in the host, >> + * and inject an interrupt if that was the case, making sure the timer is >> + * masked or disabled on the host so that we keep executing. Also schedule a >> + * software timer for the physical timer if it is enabled. >> + */ >> +void kvm_timer_flush_hwstate(struct kvm_vcpu *vcpu) >> +{ >> + struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu; >> + >> + if (unlikely(!timer->enabled)) >> + return; >> + >> + kvm_timer_update_state(vcpu); >> + >> + /* Set the background timer for the physical timer emulation. */ >> + kvm_timer_emulate(vcpu, vcpu_ptimer(vcpu)); >> + >> + if (unlikely(!irqchip_in_kernel(vcpu->kvm))) >> + kvm_timer_flush_hwstate_user(vcpu); >> + else >> + kvm_timer_flush_hwstate_vgic(vcpu); >> +} >> + >> /** >> * kvm_timer_sync_hwstate - sync timer state from cpu >> * @vcpu: The vcpu pointer >> * >> - * Check if the virtual timer has expired while we were running in the guest, >> + * Check if any of the timers have expired while we were running in the guest, >> * and inject an interrupt if that was the case. >> */ >> void kvm_timer_sync_hwstate(struct kvm_vcpu *vcpu) >> @@ -559,6 +628,13 @@ int kvm_timer_enable(struct kvm_vcpu *vcpu) >> if (timer->enabled) >> return 0; >> >> + /* Without a VGIC we do not map virtual IRQs to physical IRQs */ >> + if (!irqchip_in_kernel(vcpu->kvm)) >> + goto no_vgic; >> + >> + if (!vgic_initialized(vcpu->kvm)) >> + return -ENODEV; >> + >> /* >> * Find the physical IRQ number corresponding to the host_vtimer_irq >> */ >> @@ -582,8 +658,8 @@ int kvm_timer_enable(struct kvm_vcpu *vcpu) >> if (ret) >> return ret; >> >> +no_vgic: >> timer->enabled = 1; > > What happens if > > 1) User space spawns a VM with user space irqchip > 2) Runs the VM > 3) Then adds a virtual gic device As soon as a vcpu has run once, it is not possible to instantiate a vgic (see virt/kvm/arm/vgic/vgic-init.c:kvm_vgic_create around line 101). Thanks, M. -- Jazz is not dead. It just smells funny... From mboxrd@z Thu Jan 1 00:00:00 1970 From: marc.zyngier@arm.com (Marc Zyngier) Date: Thu, 6 Apr 2017 09:25:13 +0100 Subject: [PATCH v3 3/5] KVM: arm/arm64: Support arch timers with a userspace gic In-Reply-To: <358febe2-eb7b-93fa-fa95-ca618443f242@suse.de> References: <20170405092815.22503-1-cdall@linaro.org> <20170405092815.22503-4-cdall@linaro.org> <358febe2-eb7b-93fa-fa95-ca618443f242@suse.de> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 06/04/17 09:16, Alexander Graf wrote: > > > On 05.04.17 11:28, Christoffer Dall wrote: >> From: Alexander Graf >> >> If you're running with a userspace gic or other interrupt constroller >> (that is no vgic in the kernel), then you have so far not been able to >> use the architected timers, because the output of the architected >> timers, which are driven inside the kernel, was a kernel-only construct >> between the arch timer code and the vgic. >> >> This patch implements the new KVM_CAP_ARM_USER_IRQ feature, where we use a >> side channel on the kvm_run structure, run->s.regs.device_irq_level, to >> always notify userspace of the timer output levels when using a userspace >> irqchip. >> >> This works by ensureing that before we enter the guest, if the timer >> output level has changed compared to what we last told userspace, we >> don't enter the guest, but instead return to userspace to notify it of >> the new level. If we are exiting, because of an MMIO for example, and >> the level changed at the same time, the value is also updated and >> userspace can sample the line as it needs. This is nicely achieved >> simply always updating the timer_irq_level field after the main run >> loop. >> >> Note that the kvm_timer_update_irq trace event is changed to show the >> host IRQ number for the timer instead of the guest IRQ number, because >> the kernel no longer know which IRQ userspace wires up the timer signal >> to. >> >> Also note that this patch implements all required functionality but does >> not yet advertise the capability. >> >> Signed-off-by: Alexander Graf >> Signed-off-by: Christoffer Dall >> --- >> arch/arm/kvm/arm.c | 18 +++---- >> include/kvm/arm_arch_timer.h | 2 + >> virt/kvm/arm/arch_timer.c | 122 +++++++++++++++++++++++++++++++++++-------- >> 3 files changed, 110 insertions(+), 32 deletions(-) >> >> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c >> index 7fa4898..efb16e5 100644 >> --- a/arch/arm/kvm/arm.c >> +++ b/arch/arm/kvm/arm.c >> @@ -515,13 +515,7 @@ static int kvm_vcpu_first_run_init(struct kvm_vcpu *vcpu) >> return ret; >> } >> >> - /* >> - * Enable the arch timers only if we have an in-kernel VGIC >> - * and it has been properly initialized, since we cannot handle >> - * interrupts from the virtual timer with a userspace gic. >> - */ >> - if (irqchip_in_kernel(kvm) && vgic_initialized(kvm)) >> - ret = kvm_timer_enable(vcpu); >> + ret = kvm_timer_enable(vcpu); >> >> return ret; >> } >> @@ -640,9 +634,12 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run) >> local_irq_disable(); >> >> /* >> - * Re-check atomic conditions >> + * If we have a singal pending, or need to notify a userspace >> + * irqchip about timer level changes, then we exit (and update >> + * the timer level state in kvm_timer_update_run below). >> */ >> - if (signal_pending(current)) { >> + if (signal_pending(current) || >> + kvm_timer_should_notify_user(vcpu)) { >> ret = -EINTR; >> run->exit_reason = KVM_EXIT_INTR; >> } >> @@ -714,6 +711,9 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run) >> ret = handle_exit(vcpu, run, ret); >> } >> >> + /* Tell userspace about in-kernel device output levels */ >> + kvm_timer_update_run(vcpu); >> + >> if (vcpu->sigset_active) >> sigprocmask(SIG_SETMASK, &sigsaved, NULL); >> return ret; >> diff --git a/include/kvm/arm_arch_timer.h b/include/kvm/arm_arch_timer.h >> index fe797d6..295584f 100644 >> --- a/include/kvm/arm_arch_timer.h >> +++ b/include/kvm/arm_arch_timer.h >> @@ -63,6 +63,8 @@ int kvm_timer_vcpu_reset(struct kvm_vcpu *vcpu, >> void kvm_timer_vcpu_init(struct kvm_vcpu *vcpu); >> void kvm_timer_flush_hwstate(struct kvm_vcpu *vcpu); >> void kvm_timer_sync_hwstate(struct kvm_vcpu *vcpu); >> +bool kvm_timer_should_notify_user(struct kvm_vcpu *vcpu); >> +void kvm_timer_update_run(struct kvm_vcpu *vcpu); >> void kvm_timer_vcpu_terminate(struct kvm_vcpu *vcpu); >> >> u64 kvm_arm_timer_get_reg(struct kvm_vcpu *, u64 regid); >> diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c >> index 363f0d2..5dc2167 100644 >> --- a/virt/kvm/arm/arch_timer.c >> +++ b/virt/kvm/arm/arch_timer.c >> @@ -184,6 +184,27 @@ bool kvm_timer_should_fire(struct arch_timer_context *timer_ctx) >> return cval <= now; >> } >> >> +/* >> + * Reflect the timer output level into the kvm_run structure >> + */ >> +void kvm_timer_update_run(struct kvm_vcpu *vcpu) >> +{ >> + struct arch_timer_context *vtimer = vcpu_vtimer(vcpu); >> + struct arch_timer_context *ptimer = vcpu_ptimer(vcpu); >> + struct kvm_sync_regs *regs = &vcpu->run->s.regs; >> + >> + if (likely(irqchip_in_kernel(vcpu->kvm))) >> + return; >> + >> + /* Populate the device bitmap with the timer states */ >> + regs->device_irq_level &= ~(KVM_ARM_DEV_EL1_VTIMER | >> + KVM_ARM_DEV_EL1_PTIMER); >> + if (vtimer->irq.level) >> + regs->device_irq_level |= KVM_ARM_DEV_EL1_VTIMER; >> + if (ptimer->irq.level) >> + regs->device_irq_level |= KVM_ARM_DEV_EL1_PTIMER; >> +} >> + >> static void kvm_timer_update_irq(struct kvm_vcpu *vcpu, bool new_level, >> struct arch_timer_context *timer_ctx) >> { >> @@ -194,9 +215,12 @@ static void kvm_timer_update_irq(struct kvm_vcpu *vcpu, bool new_level, >> trace_kvm_timer_update_irq(vcpu->vcpu_id, timer_ctx->irq.irq, >> timer_ctx->irq.level); >> >> - ret = kvm_vgic_inject_irq(vcpu->kvm, vcpu->vcpu_id, timer_ctx->irq.irq, >> - timer_ctx->irq.level); >> - WARN_ON(ret); >> + if (likely(irqchip_in_kernel(vcpu->kvm))) { >> + ret = kvm_vgic_inject_irq(vcpu->kvm, vcpu->vcpu_id, >> + timer_ctx->irq.irq, >> + timer_ctx->irq.level); >> + WARN_ON(ret); >> + } >> } >> >> /* >> @@ -215,7 +239,7 @@ static void kvm_timer_update_state(struct kvm_vcpu *vcpu) >> * because the guest would never see the interrupt. Instead wait >> * until we call this function from kvm_timer_flush_hwstate. >> */ >> - if (!timer->enabled) >> + if (unlikely(!timer->enabled)) >> return; >> >> if (kvm_timer_should_fire(vtimer) != vtimer->irq.level) >> @@ -282,28 +306,12 @@ void kvm_timer_unschedule(struct kvm_vcpu *vcpu) >> timer_disarm(timer); >> } >> >> -/** >> - * kvm_timer_flush_hwstate - prepare to move the virt timer to the cpu >> - * @vcpu: The vcpu pointer >> - * >> - * Check if the virtual timer has expired while we were running in the host, >> - * and inject an interrupt if that was the case. >> - */ >> -void kvm_timer_flush_hwstate(struct kvm_vcpu *vcpu) >> +static void kvm_timer_flush_hwstate_vgic(struct kvm_vcpu *vcpu) >> { >> - struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu; >> struct arch_timer_context *vtimer = vcpu_vtimer(vcpu); >> bool phys_active; >> int ret; >> >> - if (unlikely(!timer->enabled)) >> - return; >> - >> - kvm_timer_update_state(vcpu); >> - >> - /* Set the background timer for the physical timer emulation. */ >> - kvm_timer_emulate(vcpu, vcpu_ptimer(vcpu)); >> - >> /* >> * If we enter the guest with the virtual input level to the VGIC >> * asserted, then we have already told the VGIC what we need to, and >> @@ -355,11 +363,72 @@ void kvm_timer_flush_hwstate(struct kvm_vcpu *vcpu) >> vtimer->active_cleared_last = !phys_active; >> } >> >> +bool kvm_timer_should_notify_user(struct kvm_vcpu *vcpu) >> +{ >> + struct arch_timer_context *vtimer = vcpu_vtimer(vcpu); >> + struct arch_timer_context *ptimer = vcpu_ptimer(vcpu); >> + struct kvm_sync_regs *sregs = &vcpu->run->s.regs; >> + bool vlevel, plevel; >> + >> + if (likely(irqchip_in_kernel(vcpu->kvm))) >> + return false; >> + >> + vlevel = sregs->device_irq_level & KVM_ARM_DEV_EL1_VTIMER; >> + plevel = sregs->device_irq_level & KVM_ARM_DEV_EL1_PTIMER; >> + >> + return vtimer->irq.level != vlevel || >> + ptimer->irq.level != plevel; >> +} >> + >> +static void kvm_timer_flush_hwstate_user(struct kvm_vcpu *vcpu) >> +{ >> + struct arch_timer_context *vtimer = vcpu_vtimer(vcpu); >> + >> + /* >> + * To prevent continuously exiting from the guest, we mask the >> + * physical interrupt such that the guest can make forward progress. >> + * Once we detect the output level being deasserted, we unmask the >> + * interrupt again so that we exit from the guest when the timer >> + * fires. >> + */ >> + if (vtimer->irq.level) >> + disable_percpu_irq(host_vtimer_irq); >> + else >> + enable_percpu_irq(host_vtimer_irq, 0); >> +} >> + >> +/** >> + * kvm_timer_flush_hwstate - prepare timers before running the vcpu >> + * @vcpu: The vcpu pointer >> + * >> + * Check if the virtual timer has expired while we were running in the host, >> + * and inject an interrupt if that was the case, making sure the timer is >> + * masked or disabled on the host so that we keep executing. Also schedule a >> + * software timer for the physical timer if it is enabled. >> + */ >> +void kvm_timer_flush_hwstate(struct kvm_vcpu *vcpu) >> +{ >> + struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu; >> + >> + if (unlikely(!timer->enabled)) >> + return; >> + >> + kvm_timer_update_state(vcpu); >> + >> + /* Set the background timer for the physical timer emulation. */ >> + kvm_timer_emulate(vcpu, vcpu_ptimer(vcpu)); >> + >> + if (unlikely(!irqchip_in_kernel(vcpu->kvm))) >> + kvm_timer_flush_hwstate_user(vcpu); >> + else >> + kvm_timer_flush_hwstate_vgic(vcpu); >> +} >> + >> /** >> * kvm_timer_sync_hwstate - sync timer state from cpu >> * @vcpu: The vcpu pointer >> * >> - * Check if the virtual timer has expired while we were running in the guest, >> + * Check if any of the timers have expired while we were running in the guest, >> * and inject an interrupt if that was the case. >> */ >> void kvm_timer_sync_hwstate(struct kvm_vcpu *vcpu) >> @@ -559,6 +628,13 @@ int kvm_timer_enable(struct kvm_vcpu *vcpu) >> if (timer->enabled) >> return 0; >> >> + /* Without a VGIC we do not map virtual IRQs to physical IRQs */ >> + if (!irqchip_in_kernel(vcpu->kvm)) >> + goto no_vgic; >> + >> + if (!vgic_initialized(vcpu->kvm)) >> + return -ENODEV; >> + >> /* >> * Find the physical IRQ number corresponding to the host_vtimer_irq >> */ >> @@ -582,8 +658,8 @@ int kvm_timer_enable(struct kvm_vcpu *vcpu) >> if (ret) >> return ret; >> >> +no_vgic: >> timer->enabled = 1; > > What happens if > > 1) User space spawns a VM with user space irqchip > 2) Runs the VM > 3) Then adds a virtual gic device As soon as a vcpu has run once, it is not possible to instantiate a vgic (see virt/kvm/arm/vgic/vgic-init.c:kvm_vgic_create around line 101). Thanks, M. -- Jazz is not dead. It just smells funny...