On 11/12/2018 10:20, Christoffer Dall wrote: > On Mon, Nov 26, 2018 at 06:26:44PM +0000, Julien Thierry wrote: >> To change the active state of an MMIO, halt is requested for all vcpus of >> the affected guest before modifying the IRQ state. This is done by calling >> cond_resched_lock() in vgic_mmio_change_active(). However interrupts are >> disabled at this point and we cannot reschedule a vcpu. >> >> Solve this by waiting for all vcpus to be halted after emmiting the halt >> request. >> >> Signed-off-by: Julien Thierry <[email protected]> >> Suggested-by: Marc Zyngier <[email protected]> >> Cc: Christoffer Dall <[email protected]> >> Cc: Marc Zyngier <[email protected]> >> Cc: [email protected] >> --- >> virt/kvm/arm/vgic/vgic-mmio.c | 36 ++++++++++++++---------------------- >> 1 file changed, 14 insertions(+), 22 deletions(-) >> >> diff --git a/virt/kvm/arm/vgic/vgic-mmio.c b/virt/kvm/arm/vgic/vgic-mmio.c >> index f56ff1c..5c76a92 100644 >> --- a/virt/kvm/arm/vgic/vgic-mmio.c >> +++ b/virt/kvm/arm/vgic/vgic-mmio.c >> @@ -313,27 +313,6 @@ static void vgic_mmio_change_active(struct kvm_vcpu >> *vcpu, struct vgic_irq *irq, >> >> spin_lock_irqsave(&irq->irq_lock, flags); >> >> - /* >> - * If this virtual IRQ was written into a list register, we >> - * have to make sure the CPU that runs the VCPU thread has >> - * synced back the LR state to the struct vgic_irq. >> - * >> - * As long as the conditions below are true, we know the VCPU thread >> - * may be on its way back from the guest (we kicked the VCPU thread in >> - * vgic_change_active_prepare) and still has to sync back this IRQ, >> - * so we release and re-acquire the spin_lock to let the other thread >> - * sync back the IRQ. >> - * >> - * When accessing VGIC state from user space, requester_vcpu is >> - * NULL, which is fine, because we guarantee that no VCPUs are running >> - * when accessing VGIC state from user space so irq->vcpu->cpu is >> - * always -1. >> - */ >> - while (irq->vcpu && /* IRQ may have state in an LR somewhere */ >> - irq->vcpu != requester_vcpu && /* Current thread is not the VCPU >> thread */ >> - irq->vcpu->cpu != -1) /* VCPU thread is running */ >> - cond_resched_lock(&irq->irq_lock); >> - >> if (irq->hw) { >> vgic_hw_irq_change_active(vcpu, irq, active, !requester_vcpu); >> } else { >> @@ -368,8 +347,21 @@ static void vgic_mmio_change_active(struct kvm_vcpu >> *vcpu, struct vgic_irq *irq, >> */ >> static void vgic_change_active_prepare(struct kvm_vcpu *vcpu, u32 intid) >> { >> - if (intid > VGIC_NR_PRIVATE_IRQS) >> + if (intid > VGIC_NR_PRIVATE_IRQS) { >> + struct kvm_vcpu *tmp; >> + int i; >> + >> kvm_arm_halt_guest(vcpu->kvm); >> + >> + /* Wait for each vcpu to be halted */ >> + kvm_for_each_vcpu(i, tmp, vcpu->kvm) { >> + if (tmp == vcpu) >> + continue; >> + >> + while (tmp->cpu != -1) >> + cond_resched(); >> + } > > I'm actually thinking we don't need this loop at all after the requet > rework which causes: > > 1. kvm_arm_halt_guest() to use kvm_make_all_cpus_request(kvm, > KVM_REQ_SLEEP), and > 2. KVM_REQ_SLEEP uses REQ_WAIT, and > 3. REQ_WAIT requires the VCPU to respond to IPIs before returning, and > 4. a VCPU thread can only respond when it enables interrupt, and > 5. enabling interrupts when running a VCPU only happens after syncing > the VGIC hwstate. > > Does that make sense? I'm not super familiar with what goes on with the vgic hwstate syncing, but looking at kvm_arm_halt_guest() and kvm_arch_vcpu_ioctl_run(), I agree with the reasoning. > It would be good if someone can validate this, but if it holds this > patch just becomes a nice deletion of the logic in > vgic-mmio_change_active. > As long as running kvm_vgic_sync_hwstate() on each vcpu is all that is needed before we can modify the active state, I think your solution is definitely the way to go. Thanks, -- Julien Thierry
