From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoffer Dall Subject: Re: [PATCH v9 7/9] KVM: arm/arm64: Provide a get_input_level for the arch timer Date: Mon, 22 Jan 2018 18:58:26 +0100 Message-ID: <20180122175826.GJ21802@cbox> References: <20171220113606.7030-1-christoffer.dall@linaro.org> <20171220113606.7030-8-christoffer.dall@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Marc Zyngier , Andre Przywara , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org To: Tomasz Nowicki Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu List-Id: kvm.vger.kernel.org Hi Tomasz, On Mon, Jan 22, 2018 at 01:32:57PM +0100, Tomasz Nowicki wrote: > Please see my observations/comments below. > > On 20.12.2017 12:36, Christoffer Dall wrote: > >The VGIC can now support the life-cycle of mapped level-triggered > >interrupts, and we no longer have to read back the timer state on every > >exit from the VM if we had an asserted timer interrupt signal, because > >the VGIC already knows if we hit the unlikely case where the guest > >disables the timer without ACKing the virtual timer interrupt. > > > >This means we rework a bit of the code to factor out the functionality > >to snapshot the timer state from vtimer_save_state(), and we can reuse > >this functionality in the sync path when we have an irqchip in > >userspace, and also to support our implementation of the > >get_input_level() function for the timer. > > > >This change also means that we can no longer rely on the timer's view of > >the interrupt line to set the active state, because we no longer > >maintain this state for mapped interrupts when exiting from the guest. > >Instead, we only set the active state if the virtual interrupt is > >active, and otherwise we simply let the timer fire again and raise the > >virtual interrupt from the ISR. > > > >Reviewed-by: Eric Auger > >Reviewed-by: Marc Zyngier > >Signed-off-by: Christoffer Dall > >--- > > include/kvm/arm_arch_timer.h | 2 ++ > > virt/kvm/arm/arch_timer.c | 84 ++++++++++++++++++++------------------------ > > 2 files changed, 40 insertions(+), 46 deletions(-) > > > >diff --git a/include/kvm/arm_arch_timer.h b/include/kvm/arm_arch_timer.h > >index 6e45608b2399..b1dcfde0a3ef 100644 > >--- a/include/kvm/arm_arch_timer.h > >+++ b/include/kvm/arm_arch_timer.h > >@@ -90,6 +90,8 @@ void kvm_timer_vcpu_put(struct kvm_vcpu *vcpu); > > void kvm_timer_init_vhe(void); > >+bool kvm_arch_timer_get_input_level(int vintid); > >+ > > #define vcpu_vtimer(v) (&(v)->arch.timer_cpu.vtimer) > > #define vcpu_ptimer(v) (&(v)->arch.timer_cpu.ptimer) > >diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c > >index fb0533ed903d..d845d67b7062 100644 > >--- a/virt/kvm/arm/arch_timer.c > >+++ b/virt/kvm/arm/arch_timer.c > >@@ -343,6 +343,12 @@ static void kvm_timer_update_state(struct kvm_vcpu *vcpu) > > phys_timer_emulate(vcpu); > > } > >+static void __timer_snapshot_state(struct arch_timer_context *timer) > >+{ > >+ timer->cnt_ctl = read_sysreg_el0(cntv_ctl); > >+ timer->cnt_cval = read_sysreg_el0(cntv_cval); > >+} > >+ > > static void vtimer_save_state(struct kvm_vcpu *vcpu) > > { > > struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu; > >@@ -354,10 +360,8 @@ static void vtimer_save_state(struct kvm_vcpu *vcpu) > > if (!vtimer->loaded) > > goto out; > >- if (timer->enabled) { > >- vtimer->cnt_ctl = read_sysreg_el0(cntv_ctl); > >- vtimer->cnt_cval = read_sysreg_el0(cntv_cval); > >- } > >+ if (timer->enabled) > >+ __timer_snapshot_state(vtimer); > > /* Disable the virtual timer */ > > write_sysreg_el0(0, cntv_ctl); > >@@ -454,8 +458,7 @@ static void kvm_timer_vcpu_load_vgic(struct kvm_vcpu *vcpu) > > bool phys_active; > > int ret; > >- phys_active = vtimer->irq.level || > >- kvm_vgic_map_is_active(vcpu, vtimer->irq.irq); > >+ phys_active = kvm_vgic_map_is_active(vcpu, vtimer->irq.irq); > > ret = irq_set_irqchip_state(host_vtimer_irq, > > IRQCHIP_STATE_ACTIVE, > >@@ -535,54 +538,27 @@ void kvm_timer_vcpu_put(struct kvm_vcpu *vcpu) > > set_cntvoff(0); > > } > >-static void unmask_vtimer_irq(struct kvm_vcpu *vcpu) > >+/* > >+ * With a userspace irqchip we have to check if the guest de-asserted the > >+ * timer and if so, unmask the timer irq signal on the host interrupt > >+ * controller to ensure that we see future timer signals. > >+ */ > >+static void unmask_vtimer_irq_user(struct kvm_vcpu *vcpu) > > { > > struct arch_timer_context *vtimer = vcpu_vtimer(vcpu); > > if (unlikely(!irqchip_in_kernel(vcpu->kvm))) { > >- kvm_vtimer_update_mask_user(vcpu); > >- return; > >- } > >- > >- /* > >- * If the guest disabled the timer without acking the interrupt, then > >- * we must make sure the physical and virtual active states are in > >- * sync by deactivating the physical interrupt, because otherwise we > >- * wouldn't see the next timer interrupt in the host. > >- */ > >- if (!kvm_vgic_map_is_active(vcpu, vtimer->irq.irq)) { > >- int ret; > >- ret = irq_set_irqchip_state(host_vtimer_irq, > >- IRQCHIP_STATE_ACTIVE, > >- false); > >- WARN_ON(ret); > >+ __timer_snapshot_state(vtimer); > >+ if (!kvm_timer_should_fire(vtimer)) { > >+ kvm_timer_update_irq(vcpu, false, vtimer); > >+ kvm_vtimer_update_mask_user(vcpu); > >+ } > > } > > } > >-/** > >- * kvm_timer_sync_hwstate - sync timer state from cpu > >- * @vcpu: The vcpu pointer > >- * > >- * 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) > > { > >- struct arch_timer_context *vtimer = vcpu_vtimer(vcpu); > >- > >- /* > >- * If we entered the guest with the vtimer output asserted we have to > >- * check if the guest has modified the timer so that we should lower > >- * the line at this point. > >- */ > >- if (vtimer->irq.level) { > >- vtimer->cnt_ctl = read_sysreg_el0(cntv_ctl); > >- vtimer->cnt_cval = read_sysreg_el0(cntv_cval); > >- if (!kvm_timer_should_fire(vtimer)) { > >- kvm_timer_update_irq(vcpu, false, vtimer); > >- unmask_vtimer_irq(vcpu); > >- } > >- } > >+ unmask_vtimer_irq_user(vcpu); > > } > > While testing your VHE optimization series [1] I noticed massive WFI exits > on ThunderX2 so I bisected 'vhe-optimize-v3-with-fixes' branch of [2] down > to this commit. Thanks for doing that! > > The host traps on WFI so that VCPU thread should be scheduled out for some > time. However, this is not happening because kvm_vcpu_block() -> > kvm_vcpu_check_block() gives negative value (vtimer->irq.level is asserted) > and VCPU is woken up immediately. Nobody takes care about lowering the > vtimer line in this case. Indeed, this is a problem. I thought this was properly handled, but I think this part changed at some version of these patches. > > I reverted shape of above kvm_timer_sync_hwstate() and things are good now. > Before I start digging I wanted to check with you. Can you please check on > your side? I'd still like to not have kvm_timer_sync_hwstate() do any work, and I think this can be accomplished by updating vtimer->irq.level in vtimer_save_state(). I didn't observe that a guest couldn't sleep on WFI when I tested this series, but I may have simply not noticed it on any of the platforms I used for testing. I'll investigate and come back to you. Thanks, -Christoffer From mboxrd@z Thu Jan 1 00:00:00 1970 From: christoffer.dall@linaro.org (Christoffer Dall) Date: Mon, 22 Jan 2018 18:58:26 +0100 Subject: [PATCH v9 7/9] KVM: arm/arm64: Provide a get_input_level for the arch timer In-Reply-To: References: <20171220113606.7030-1-christoffer.dall@linaro.org> <20171220113606.7030-8-christoffer.dall@linaro.org> Message-ID: <20180122175826.GJ21802@cbox> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Hi Tomasz, On Mon, Jan 22, 2018 at 01:32:57PM +0100, Tomasz Nowicki wrote: > Please see my observations/comments below. > > On 20.12.2017 12:36, Christoffer Dall wrote: > >The VGIC can now support the life-cycle of mapped level-triggered > >interrupts, and we no longer have to read back the timer state on every > >exit from the VM if we had an asserted timer interrupt signal, because > >the VGIC already knows if we hit the unlikely case where the guest > >disables the timer without ACKing the virtual timer interrupt. > > > >This means we rework a bit of the code to factor out the functionality > >to snapshot the timer state from vtimer_save_state(), and we can reuse > >this functionality in the sync path when we have an irqchip in > >userspace, and also to support our implementation of the > >get_input_level() function for the timer. > > > >This change also means that we can no longer rely on the timer's view of > >the interrupt line to set the active state, because we no longer > >maintain this state for mapped interrupts when exiting from the guest. > >Instead, we only set the active state if the virtual interrupt is > >active, and otherwise we simply let the timer fire again and raise the > >virtual interrupt from the ISR. > > > >Reviewed-by: Eric Auger > >Reviewed-by: Marc Zyngier > >Signed-off-by: Christoffer Dall > >--- > > include/kvm/arm_arch_timer.h | 2 ++ > > virt/kvm/arm/arch_timer.c | 84 ++++++++++++++++++++------------------------ > > 2 files changed, 40 insertions(+), 46 deletions(-) > > > >diff --git a/include/kvm/arm_arch_timer.h b/include/kvm/arm_arch_timer.h > >index 6e45608b2399..b1dcfde0a3ef 100644 > >--- a/include/kvm/arm_arch_timer.h > >+++ b/include/kvm/arm_arch_timer.h > >@@ -90,6 +90,8 @@ void kvm_timer_vcpu_put(struct kvm_vcpu *vcpu); > > void kvm_timer_init_vhe(void); > >+bool kvm_arch_timer_get_input_level(int vintid); > >+ > > #define vcpu_vtimer(v) (&(v)->arch.timer_cpu.vtimer) > > #define vcpu_ptimer(v) (&(v)->arch.timer_cpu.ptimer) > >diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c > >index fb0533ed903d..d845d67b7062 100644 > >--- a/virt/kvm/arm/arch_timer.c > >+++ b/virt/kvm/arm/arch_timer.c > >@@ -343,6 +343,12 @@ static void kvm_timer_update_state(struct kvm_vcpu *vcpu) > > phys_timer_emulate(vcpu); > > } > >+static void __timer_snapshot_state(struct arch_timer_context *timer) > >+{ > >+ timer->cnt_ctl = read_sysreg_el0(cntv_ctl); > >+ timer->cnt_cval = read_sysreg_el0(cntv_cval); > >+} > >+ > > static void vtimer_save_state(struct kvm_vcpu *vcpu) > > { > > struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu; > >@@ -354,10 +360,8 @@ static void vtimer_save_state(struct kvm_vcpu *vcpu) > > if (!vtimer->loaded) > > goto out; > >- if (timer->enabled) { > >- vtimer->cnt_ctl = read_sysreg_el0(cntv_ctl); > >- vtimer->cnt_cval = read_sysreg_el0(cntv_cval); > >- } > >+ if (timer->enabled) > >+ __timer_snapshot_state(vtimer); > > /* Disable the virtual timer */ > > write_sysreg_el0(0, cntv_ctl); > >@@ -454,8 +458,7 @@ static void kvm_timer_vcpu_load_vgic(struct kvm_vcpu *vcpu) > > bool phys_active; > > int ret; > >- phys_active = vtimer->irq.level || > >- kvm_vgic_map_is_active(vcpu, vtimer->irq.irq); > >+ phys_active = kvm_vgic_map_is_active(vcpu, vtimer->irq.irq); > > ret = irq_set_irqchip_state(host_vtimer_irq, > > IRQCHIP_STATE_ACTIVE, > >@@ -535,54 +538,27 @@ void kvm_timer_vcpu_put(struct kvm_vcpu *vcpu) > > set_cntvoff(0); > > } > >-static void unmask_vtimer_irq(struct kvm_vcpu *vcpu) > >+/* > >+ * With a userspace irqchip we have to check if the guest de-asserted the > >+ * timer and if so, unmask the timer irq signal on the host interrupt > >+ * controller to ensure that we see future timer signals. > >+ */ > >+static void unmask_vtimer_irq_user(struct kvm_vcpu *vcpu) > > { > > struct arch_timer_context *vtimer = vcpu_vtimer(vcpu); > > if (unlikely(!irqchip_in_kernel(vcpu->kvm))) { > >- kvm_vtimer_update_mask_user(vcpu); > >- return; > >- } > >- > >- /* > >- * If the guest disabled the timer without acking the interrupt, then > >- * we must make sure the physical and virtual active states are in > >- * sync by deactivating the physical interrupt, because otherwise we > >- * wouldn't see the next timer interrupt in the host. > >- */ > >- if (!kvm_vgic_map_is_active(vcpu, vtimer->irq.irq)) { > >- int ret; > >- ret = irq_set_irqchip_state(host_vtimer_irq, > >- IRQCHIP_STATE_ACTIVE, > >- false); > >- WARN_ON(ret); > >+ __timer_snapshot_state(vtimer); > >+ if (!kvm_timer_should_fire(vtimer)) { > >+ kvm_timer_update_irq(vcpu, false, vtimer); > >+ kvm_vtimer_update_mask_user(vcpu); > >+ } > > } > > } > >-/** > >- * kvm_timer_sync_hwstate - sync timer state from cpu > >- * @vcpu: The vcpu pointer > >- * > >- * 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) > > { > >- struct arch_timer_context *vtimer = vcpu_vtimer(vcpu); > >- > >- /* > >- * If we entered the guest with the vtimer output asserted we have to > >- * check if the guest has modified the timer so that we should lower > >- * the line at this point. > >- */ > >- if (vtimer->irq.level) { > >- vtimer->cnt_ctl = read_sysreg_el0(cntv_ctl); > >- vtimer->cnt_cval = read_sysreg_el0(cntv_cval); > >- if (!kvm_timer_should_fire(vtimer)) { > >- kvm_timer_update_irq(vcpu, false, vtimer); > >- unmask_vtimer_irq(vcpu); > >- } > >- } > >+ unmask_vtimer_irq_user(vcpu); > > } > > While testing your VHE optimization series [1] I noticed massive WFI exits > on ThunderX2 so I bisected 'vhe-optimize-v3-with-fixes' branch of [2] down > to this commit. Thanks for doing that! > > The host traps on WFI so that VCPU thread should be scheduled out for some > time. However, this is not happening because kvm_vcpu_block() -> > kvm_vcpu_check_block() gives negative value (vtimer->irq.level is asserted) > and VCPU is woken up immediately. Nobody takes care about lowering the > vtimer line in this case. Indeed, this is a problem. I thought this was properly handled, but I think this part changed at some version of these patches. > > I reverted shape of above kvm_timer_sync_hwstate() and things are good now. > Before I start digging I wanted to check with you. Can you please check on > your side? I'd still like to not have kvm_timer_sync_hwstate() do any work, and I think this can be accomplished by updating vtimer->irq.level in vtimer_save_state(). I didn't observe that a guest couldn't sleep on WFI when I tested this series, but I may have simply not noticed it on any of the platforms I used for testing. I'll investigate and come back to you. Thanks, -Christoffer