On 20/11/2018 14:18, Christoffer Dall wrote:
On Mon, Nov 19, 2018 at 05:07:56PM +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 running a vcpu cannot get rescheduled.
"running a vcpu cannot get rescheduled" ?
Solve this by waiting for all vcpus to be halted after emmiting the halt request.
Fixes commit 6c1b7521f4a07cc63bbe2dfe290efed47cdb780a ("KVM: arm/arm64: Factor out functionality to get vgic mmio requester_vcpu")
Signed-off-by: Julien Thierry julien.thierry@arm.com Suggested-by: Marc Zyngier marc.zyngier@arm.com Cc: Christoffer Dall christoffer.dall@arm.com Cc: Marc Zyngier marc.zyngier@arm.com Cc: stable@vger.kernel.org
virt/kvm/arm/vgic/vgic-mmio.c | 33 +++++++++++---------------------- 1 file changed, 11 insertions(+), 22 deletions(-)
diff --git a/virt/kvm/arm/vgic/vgic-mmio.c b/virt/kvm/arm/vgic/vgic-mmio.c index f56ff1c..eefd877 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 +347,18 @@ 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) {while (tmp->cpu != -1)cond_resched();We used to have something like this which Andre then found out it could deadlock the system, because the VCPU making this request wouldn't have called kvm_arch_vcpu_put, and its cpu value would still have a value.
That's why we have the vcpu && vcpu != requester check.
Ah, I now remember that one. I guess it is a matter of skipping the requester vcpu in the kvm_for_each_vcpu loop.
Thanks,
M.