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

Andrew Jones
2017-06-01T10:59:25Z

On Thu, Jun 01, 2017 at 12:35:33PM +0200, Christoffer Dall wrote:
> 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 :(

We need a kvm_check_request() to pair with a requesting VCPU's setting
of virtual irq state and call of kvm_make_request(). The requester's
kvm_make_request() ensures the target VCPU executes VCPU RUN, and the
barriers wrapped in kvm_check/make_request() ensure that when VCPU RUN
calls kvm_vgic_flush_hwstate() that the virtual irq state set by the
requester is visible to the target VCPU.

But you knew all that already :-) So, maybe I just need to replace
'all hardware state we need to flush should now be visible.' with
'the virtual irq state is now visible.'?

>
> 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);
>
> ?

I won't insist, but I prefer the empty function to breaking the pattern
of this if-sequence, and also to the calling of a function named "check"
without considering its return value.

>
> > }
> > }
> >
> > @@ -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>

Thanks,
drew