On Wed, 20 Dec 2017 11:36:05 +0000,
Christoffer Dall wrote:
>
> We currently check if the VM has a userspace irqchip in several places
> along the critical path, and if so, we do some work which is only
> required for having an irqchip in userspace. This is unfortunate, as we
> could avoid doing any work entirely, if we didn't have to support
> irqchip in userspace.
>
> Realizing the userspace irqchip on ARM is mostly a developer or hobby
> feature, and is unlikely to be used in servers or other scenarios where
> performance is a priority, we can use a refcounted static key to only
> check the irqchip configuration when we have at least one VM that uses
> an irqchip in userspace.
>
> Signed-off-by: Christoffer Dall <christoffer.dall@xxxxxxxxxx>
> ---
> arch/arm/include/asm/kvm_host.h | 2 ++
> arch/arm64/include/asm/kvm_host.h | 2 ++
> virt/kvm/arm/arch_timer.c | 6 ++--
> virt/kvm/arm/arm.c | 59 ++++++++++++++++++++++++++++-----------
> 4 files changed, 50 insertions(+), 19 deletions(-)
>
> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
> index a9f7d3f47134..6394fb99da7f 100644
> --- a/arch/arm/include/asm/kvm_host.h
> +++ b/arch/arm/include/asm/kvm_host.h
> @@ -48,6 +48,8 @@
> KVM_ARCH_REQ_FLAGS(0, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
> #define KVM_REQ_IRQ_PENDING KVM_ARCH_REQ(1)
>
> +DECLARE_STATIC_KEY_FALSE(userspace_irqchip_in_use);
> +
> u32 *kvm_vcpu_reg(struct kvm_vcpu *vcpu, u8 reg_num, u32 mode);
> int __attribute_const__ kvm_target_cpu(void);
> int kvm_reset_vcpu(struct kvm_vcpu *vcpu);
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index ea6cb5b24258..e7218cf7df2a 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -47,6 +47,8 @@
> KVM_ARCH_REQ_FLAGS(0, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
> #define KVM_REQ_IRQ_PENDING KVM_ARCH_REQ(1)
>
> +DECLARE_STATIC_KEY_FALSE(userspace_irqchip_in_use);
> +
> int __attribute_const__ kvm_target_cpu(void);
> int kvm_reset_vcpu(struct kvm_vcpu *vcpu);
> int kvm_arch_dev_ioctl_check_extension(struct kvm *kvm, long ext);
> diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c
> index d845d67b7062..cfcd0323deab 100644
> --- a/virt/kvm/arm/arch_timer.c
> +++ b/virt/kvm/arm/arch_timer.c
> @@ -103,7 +103,8 @@ static irqreturn_t kvm_arch_timer_handler(int irq, void *dev_id)
> if (kvm_timer_irq_can_fire(vtimer))
> kvm_timer_update_irq(vcpu, true, vtimer);
>
> - if (unlikely(!irqchip_in_kernel(vcpu->kvm)))
> + if (static_branch_unlikely(&userspace_irqchip_in_use) &&
> + unlikely(!irqchip_in_kernel(vcpu->kvm)))
> kvm_vtimer_update_mask_user(vcpu);
>
> return IRQ_HANDLED;
> @@ -284,7 +285,8 @@ 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);
>
> - if (likely(irqchip_in_kernel(vcpu->kvm))) {
> + if (!static_branch_unlikely(&userspace_irqchip_in_use) &&
> + likely(irqchip_in_kernel(vcpu->kvm))) {
> ret = kvm_vgic_inject_irq(vcpu->kvm, vcpu->vcpu_id,
> timer_ctx->irq.irq,
> timer_ctx->irq.level,
> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> index 3610e132df8b..0cf0459134ff 100644
> --- a/virt/kvm/arm/arm.c
> +++ b/virt/kvm/arm/arm.c
> @@ -74,6 +74,8 @@ static void kvm_arm_set_running_vcpu(struct kvm_vcpu *vcpu)
> __this_cpu_write(kvm_arm_running_vcpu, vcpu);
> }
>
> +DEFINE_STATIC_KEY_FALSE(userspace_irqchip_in_use);
> +
> /**
> * kvm_arm_get_running_vcpu - get the vcpu running on the current CPU.
> * Must be called from non-preemptible context
> @@ -302,6 +304,8 @@ void kvm_arch_vcpu_free(struct kvm_vcpu *vcpu)
>
> void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
> {
> + if (vcpu->arch.has_run_once && unlikely(!irqchip_in_kernel(vcpu->kvm)))
> + static_branch_dec(&userspace_irqchip_in_use);
> kvm_arch_vcpu_free(vcpu);
> }
>
> @@ -522,14 +526,22 @@ static int kvm_vcpu_first_run_init(struct kvm_vcpu *vcpu)
>
> vcpu->arch.has_run_once = true;
>
> - /*
> - * Map the VGIC hardware resources before running a vcpu the first
> - * time on this VM.
> - */
> - if (unlikely(irqchip_in_kernel(kvm) && !vgic_ready(kvm))) {
> - ret = kvm_vgic_map_resources(kvm);
> - if (ret)
> - return ret;
> + if (likely(irqchip_in_kernel(kvm))) {
> + /*
> + * Map the VGIC hardware resources before running a vcpu the
> + * first time on this VM.
> + */
> + if (unlikely(!vgic_ready(kvm))) {
> + ret = kvm_vgic_map_resources(kvm);
> + if (ret)
> + return ret;
> + }
> + } else {
> + /*
> + * Tell the rest of the code that there are userspace irqchip
> + * VMs in the wild.
> + */
> + static_branch_inc(&userspace_irqchip_in_use);
> }
>
> ret = kvm_timer_enable(vcpu);
> @@ -664,18 +676,29 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
> kvm_vgic_flush_hwstate(vcpu);
>
> /*
> - * If we have a singal pending, or need to notify a userspace
> - * irqchip about timer or PMU level changes, then we exit (and
> - * update the timer level state in kvm_timer_update_run
> - * below).
> + * Exit if we have a singal pending so that we can deliver the
nit: s/singal/signal/
> + * signal to user space.
> */
> - if (signal_pending(current) ||
> - kvm_timer_should_notify_user(vcpu) ||
> - kvm_pmu_should_notify_user(vcpu)) {
> + if (signal_pending(current)) {
> ret = -EINTR;
> run->exit_reason = KVM_EXIT_INTR;
> }
>
> + /*
> + * If we're using a userspace irqchip, then check if we need
> + * to tell a userspace irqchip about timer or PMU level
> + * changes and if so, exit to userspace (the actual level
> + * state gets updated in kvm_timer_update_run and
> + * kvm_pmu_update_run below.
nit: missing closing parenthesis.
> + */
> + if (static_branch_unlikely(&userspace_irqchip_in_use)) {
> + if (kvm_timer_should_notify_user(vcpu) ||
> + kvm_pmu_should_notify_user(vcpu)) {
> + ret = -EINTR;
> + run->exit_reason = KVM_EXIT_INTR;
> + }
> + }
> +
> /*
> * Ensure we set mode to IN_GUEST_MODE after we disable
> * interrupts and before the final VCPU requests check.
> @@ -688,7 +711,8 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
> kvm_request_pending(vcpu)) {
> vcpu->mode = OUTSIDE_GUEST_MODE;
> kvm_pmu_sync_hwstate(vcpu);
> - kvm_timer_sync_hwstate(vcpu);
> + if (static_branch_unlikely(&userspace_irqchip_in_use))
> + kvm_timer_sync_hwstate(vcpu);
> kvm_vgic_sync_hwstate(vcpu);
> local_irq_enable();
> preempt_enable();
> @@ -732,7 +756,8 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
> * we don't want vtimer interrupts to race with syncing the
> * timer virtual interrupt state.
> */
> - kvm_timer_sync_hwstate(vcpu);
> + if (static_branch_unlikely(&userspace_irqchip_in_use))
> + kvm_timer_sync_hwstate(vcpu);
>
> /*
> * We may have taken a host interrupt in HYP mode (ie
> --
> 2.14.2
>
Other than the trivial nits above:
Reviewed-by: Marc Zyngier <marc.zyngier@xxxxxxx>
M.
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