Re: [PATCH v4 09/11] KVM: arm/arm64: use vcpu requests for irq injection

Christoffer Dall
2017-06-01T10:35:33Z

On Tue, May 16, 2017 at 04:20:33AM +0200, Andrew Jones wrote:
> Don't use request-less VCPU kicks when injecting IRQs, as a VCPU
> kick meant to trigger the interrupt injection could be sent while
> the VCPU is outside guest mode, which means no IPI is sent, and
> after it has called kvm_vgic_flush_hwstate(), meaning it won't see
> the updated GIC state until its next exit some time later for some
> other reason. The receiving VCPU only needs to check this request
> in VCPU RUN to handle it. By checking it, if it's pending, a
> memory barrier will be issued that ensures all state is visible.
> We still create a vcpu_req_irq_pending() function (which is a nop),
> though, in order to allow us to use the standard request checking
> pattern.
>
> Signed-off-by: Andrew Jones <drjones@redhat.com>
> ---
> arch/arm/include/asm/kvm_host.h | 1 +
> arch/arm64/include/asm/kvm_host.h | 1 +
> virt/kvm/arm/arm.c | 12 ++++++++++++
> virt/kvm/arm/vgic/vgic.c | 9 +++++++--
> 4 files changed, 21 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
> index fdd644c01c89..00ad56ee6455 100644
> --- a/arch/arm/include/asm/kvm_host.h
> +++ b/arch/arm/include/asm/kvm_host.h
> @@ -46,6 +46,7 @@
>
> #define KVM_REQ_SLEEP \
> KVM_ARCH_REQ_FLAGS(0, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
> +#define KVM_REQ_IRQ_PENDING KVM_ARCH_REQ(1)
>
> u32 *kvm_vcpu_reg(struct kvm_vcpu *vcpu, u8 reg_num, u32 mode);
> int __attribute_const__ kvm_target_cpu(void);
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 9bd0d1040de9..0c4fd1f46e10 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -43,6 +43,7 @@
>
> #define KVM_REQ_SLEEP \
> KVM_ARCH_REQ_FLAGS(0, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
> +#define KVM_REQ_IRQ_PENDING KVM_ARCH_REQ(1)
>
> int __attribute_const__ kvm_target_cpu(void);
> int kvm_reset_vcpu(struct kvm_vcpu *vcpu);
> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> index ddc833987dfb..73a75ca91e41 100644
> --- a/virt/kvm/arm/arm.c
> +++ b/virt/kvm/arm/arm.c
> @@ -570,6 +570,15 @@ static void vcpu_req_sleep(struct kvm_vcpu *vcpu)
> }
> }
>
> +static void vcpu_req_irq_pending(struct kvm_vcpu *vcpu)
> +{
> + /*
> + * Nothing to do here. kvm_check_request() already issued a memory
> + * barrier that pairs with kvm_make_request(), so all hardware state
> + * we need to flush should now be visible.
> + */

I don't understand this comment :(

And I don't much like this empty function either.

> +}
> +
> static int kvm_vcpu_initialized(struct kvm_vcpu *vcpu)
> {
> return vcpu->arch.target >= 0;
> @@ -580,6 +589,8 @@ static void check_vcpu_requests(struct kvm_vcpu *vcpu)
> if (kvm_request_pending(vcpu)) {
> if (kvm_check_request(KVM_REQ_SLEEP, vcpu))
> vcpu_req_sleep(vcpu);
> + if (kvm_check_request(KVM_REQ_IRQ_PENDING, vcpu))
> + vcpu_req_irq_pending(vcpu);

Can we just do:
/*
* Clear IRQ_PENDING requests that were made to
* guarantee that a VCPU sees new virtual interrupts.
*/
kvm_check_request(KVM_REQ_IRQ_PENDING, vcpu);

?

> }
> }
>
> @@ -771,6 +782,7 @@ static int vcpu_interrupt_line(struct kvm_vcpu *vcpu, int number, bool level)
> * trigger a world-switch round on the running physical CPU to set the
> * virtual IRQ/FIQ fields in the HCR appropriately.
> */
> + kvm_make_request(KVM_REQ_IRQ_PENDING, vcpu);
> kvm_vcpu_kick(vcpu);
>
> return 0;
> diff --git a/virt/kvm/arm/vgic/vgic.c b/virt/kvm/arm/vgic/vgic.c
> index aea080a2c443..c66feaca2a5d 100644
> --- a/virt/kvm/arm/vgic/vgic.c
> +++ b/virt/kvm/arm/vgic/vgic.c
> @@ -286,8 +286,10 @@ bool vgic_queue_irq_unlock(struct kvm *kvm, struct vgic_irq *irq)
> * won't see this one until it exits for some other
> * reason.
> */
> - if (vcpu)
> + if (vcpu) {
> + kvm_make_request(KVM_REQ_IRQ_PENDING, vcpu);
> kvm_vcpu_kick(vcpu);
> + }
> return false;
> }
>
> @@ -333,6 +335,7 @@ bool vgic_queue_irq_unlock(struct kvm *kvm, struct vgic_irq *irq)
> spin_unlock(&irq->irq_lock);
> spin_unlock(&vcpu->arch.vgic_cpu.ap_list_lock);
>
> + kvm_make_request(KVM_REQ_IRQ_PENDING, vcpu);
> kvm_vcpu_kick(vcpu);
>
> return true;
> @@ -722,8 +725,10 @@ void vgic_kick_vcpus(struct kvm *kvm)
> * a good kick...
> */
> kvm_for_each_vcpu(c, vcpu, kvm) {
> - if (kvm_vgic_vcpu_pending_irq(vcpu))
> + if (kvm_vgic_vcpu_pending_irq(vcpu)) {
> + kvm_make_request(KVM_REQ_IRQ_PENDING, vcpu);
> kvm_vcpu_kick(vcpu);
> + }
> }
> }
>
> --
> 2.9.3
>
Otherwise:

Reviewed-by: Christoffer Dall <cdall@linaro.org>