| Message ID | 1543256807-9768-2-git-send-email-julien.thierry@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: arm/arm64: vgic: Use raw_spinlock for locks taken in IRQ context | expand |
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 <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 | 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? 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. Thanks, Christoffer
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 <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 | 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,
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(); + } + } } /* See vgic_change_active_prepare */
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 <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 | 36 ++++++++++++++---------------------- 1 file changed, 14 insertions(+), 22 deletions(-)