Re: [PATCH v3 09/10] KVM: arm/arm64: use vcpu requests for irq injection

Andrew Jones
2017-05-09T17:54:05Z

On Sat, May 06, 2017 at 08:51:00PM +0200, Christoffer Dall wrote:
> Hi Drew,
>
> On Wed, May 03, 2017 at 06:06:34PM +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/arm/kvm/arm.c | 12 ++++++++++++
> > arch/arm64/include/asm/kvm_host.h | 1 +
> > virt/kvm/arm/arch_timer.c | 1 +
> > virt/kvm/arm/vgic/vgic.c | 9 +++++++--
> > 5 files changed, 22 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
> > index 41669578b3df..7bf90aaf2e87 100644
> > --- a/arch/arm/include/asm/kvm_host.h
> > +++ b/arch/arm/include/asm/kvm_host.h
> > @@ -47,6 +47,7 @@
> >
> > #define KVM_REQ_SLEEP \
> > KVM_ARCH_REQ_FLAGS(0, KVM_REQUEST_NO_WAKEUP | KVM_REQUEST_WAIT)
> > +#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/arm/kvm/arm.c b/arch/arm/kvm/arm.c
> > index d62e99885434..330064475914 100644
> > --- a/arch/arm/kvm/arm.c
> > +++ b/arch/arm/kvm/arm.c
> > @@ -581,6 +581,15 @@ static void vcpu_req_sleep(struct kvm_vcpu *vcpu)
> > (!vcpu->arch.pause)));
> > }
> >
> > +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.
> > + */
> > +}
> > +
> > static int kvm_vcpu_initialized(struct kvm_vcpu *vcpu)
> > {
> > return vcpu->arch.target >= 0;
> > @@ -634,6 +643,8 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
> > 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);
> > }
> >
> > /*
> > @@ -777,6 +788,7 @@ 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/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> > index 04c0f9d37386..2c33fef945fe 100644
> > --- a/arch/arm64/include/asm/kvm_host.h
> > +++ b/arch/arm64/include/asm/kvm_host.h
> > @@ -44,6 +44,7 @@
> >
> > #define KVM_REQ_SLEEP \
> > KVM_ARCH_REQ_FLAGS(0, KVM_REQUEST_NO_WAKEUP | KVM_REQUEST_WAIT)
> > +#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/arch_timer.c b/virt/kvm/arm/arch_timer.c
> > index 5976609ef27c..469b43315c0a 100644
> > --- a/virt/kvm/arm/arch_timer.c
> > +++ b/virt/kvm/arm/arch_timer.c
> > @@ -95,6 +95,7 @@ static void kvm_timer_inject_irq_work(struct work_struct *work)
> > * If the vcpu is blocked we want to wake it up so that it will see
> > * the timer has expired when entering the guest.
> > */
> > + kvm_make_request(KVM_REQ_IRQ_PENDING, vcpu);
> > kvm_vcpu_kick(vcpu);
>
> So I think we just call kvm_vcpu_kick() because it calls
> kvm_vcpu_wake_up(). If we have this timer work happening, it means that
> the VCPU is blocked, and there won't be a race with executing in the run
> loop, right?
>
> So maybe we should just change this kvm_vcpu_kick() to a direct call to
> kvm_vcpu_wake_up() to avoid having a request-less kick.
>
> Note that your change will still work, I just think it's unnecessary.

Ah, yes. I like the idea of changing it to a wake up. Will do.

Thanks,
drew

>
> Thanks,
> -Christoffer
>
> > }
> >
> > diff --git a/virt/kvm/arm/vgic/vgic.c b/virt/kvm/arm/vgic/vgic.c
> > index 3d0979c30721..bdd4b3a953b5 100644
> > --- a/virt/kvm/arm/vgic/vgic.c
> > +++ b/virt/kvm/arm/vgic/vgic.c
> > @@ -283,8 +283,10 @@ 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;
> > }
> >
> > @@ -330,6 +332,7 @@ 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;
> > @@ -719,8 +722,10 @@ 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
> >