On Sun, Dec 14, 2014 at 11:33:04AM +0000, Marc Zyngier wrote: > On Sat, Dec 13 2014 at 11:17:29 AM, Christoffer Dall > <[email protected]> wrote: > > It is curently possible to run a VM with architected timers support > > without creating an in-kernel VGIC, which will result in interrupts from > > the virtual timer going nowhere. > > > > To address this issue, move the architected timers initialization to the > > time when we run a VCPU for the first time, and then only initialize > > (and enable) the architected timers if we have a properly created and > > initialized in-kernel VGIC. > > > > When injecting interrupts from the virtual timer to the vgic, the > > current setup should ensure that this never calls an on-demand init of > > the VGIC, which is the only call path that could return an error from > > kvm_vgic_inject_irq(), so capture the return value and raise a warning > > if there's an error there. > > > > We also change the kvm_timer_init() function from returning an int to be > > a void function, since the function always succeeds. > > > > Signed-off-by: Christoffer Dall <[email protected]> > > --- > > arch/arm/kvm/arm.c | 15 +++++++++++---- > > include/kvm/arm_arch_timer.h | 2 +- > > virt/kvm/arm/arch_timer.c | 15 ++++++++++----- > > 3 files changed, 22 insertions(+), 10 deletions(-) > > > > diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c > > index d4da244..06f0431 100644 > > --- a/arch/arm/kvm/arm.c > > +++ b/arch/arm/kvm/arm.c > > @@ -127,8 +127,6 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long > > type) > > if (ret) > > goto out_free_stage2_pgd; > > > > - kvm_timer_init(kvm); > > - > > /* Mark the initial VMID generation invalid */ > > kvm->arch.vmid_gen = 0; > > > > @@ -424,6 +422,7 @@ static void update_vttbr(struct kvm *kvm) > > > > static int kvm_vcpu_first_run_init(struct kvm_vcpu *vcpu) > > { > > + struct kvm *kvm = vcpu->kvm; > > int ret; > > > > if (likely(vcpu->arch.has_run_once)) > > @@ -435,12 +434,20 @@ static int kvm_vcpu_first_run_init(struct kvm_vcpu > > *vcpu) > > * Map the VGIC hardware resources before running a vcpu the first > > * time on this VM. > > */ > > - if (unlikely(!vgic_ready(vcpu->kvm))) { > > - ret = kvm_vgic_map_resources(vcpu->kvm); > > + if (unlikely(!vgic_ready(kvm))) { > > + ret = kvm_vgic_map_resources(kvm); > > if (ret) > > return ret; > > } > > > > + /* > > + * Initialize the Architected Timers only if we have an in-kernel VGIC > > + * and it has been properly initialized, since we cannot handle > > + * interrupts from the virtual timer with a userspace vgic. > > + */ > > + if (irqchip_in_kernel(kvm) && vgic_initialized(kvm)) > > + kvm_timer_init(kvm); > > + > > return 0; > > } > > > > diff --git a/include/kvm/arm_arch_timer.h b/include/kvm/arm_arch_timer.h > > index ad9db60..c9bd045 100644 > > --- a/include/kvm/arm_arch_timer.h > > +++ b/include/kvm/arm_arch_timer.h > > @@ -60,7 +60,7 @@ struct arch_timer_cpu { > > > > #ifdef CONFIG_KVM_ARM_TIMER > > int kvm_timer_hyp_init(void); > > -int kvm_timer_init(struct kvm *kvm); > > +void kvm_timer_init(struct kvm *kvm); > > void kvm_timer_vcpu_reset(struct kvm_vcpu *vcpu, > > const struct kvm_irq_level *irq); > > void kvm_timer_vcpu_init(struct kvm_vcpu *vcpu); > > diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c > > index 22fa819..48ce5cb 100644 > > --- a/virt/kvm/arm/arch_timer.c > > +++ b/virt/kvm/arm/arch_timer.c > > @@ -61,12 +61,14 @@ static void timer_disarm(struct arch_timer_cpu *timer) > > > > static void kvm_timer_inject_irq(struct kvm_vcpu *vcpu) > > { > > + int ret; > > struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu; > > > > timer->cntv_ctl |= ARCH_TIMER_CTRL_IT_MASK; > > - kvm_vgic_inject_irq(vcpu->kvm, vcpu->vcpu_id, > > - timer->irq->irq, > > - timer->irq->level); > > + ret = kvm_vgic_inject_irq(vcpu->kvm, vcpu->vcpu_id, > > + timer->irq->irq, > > + timer->irq->level); > > + WARN_ON(ret); > > } > > > > static irqreturn_t kvm_arch_timer_handler(int irq, void *dev_id) > > @@ -307,12 +309,15 @@ void kvm_timer_vcpu_terminate(struct kvm_vcpu *vcpu) > > timer_disarm(timer); > > } > > > > -int kvm_timer_init(struct kvm *kvm) > > +void kvm_timer_init(struct kvm *kvm) > > { > > + if (kvm->arch.timer.enabled) > > + return; > > + > > if (timecounter && wqueue) { > > kvm->arch.timer.cntvoff = kvm_phys_timer_read(); > > kvm->arch.timer.enabled = 1; > > } > > Be careful, you've now introduced a race between two vcpus doing their > "first run" at the same time. The consequence is fairly minor (only the > virtual offset is affected, and that's unlikely to cause any ill effect > that early in the life of the VM), but still. > > We can decide that this is not big enough a deal to warrant a lock, but > that definitely deserves a comment.
That escaped my attention completely, thanks for spotting it. > > Another thing to consider is how this works with restoring a VM. We > relied on the fact that CNTVOFF is set by system register accesses after > the timer init, but we're now overriding the value. Am I missing > something crucial? > The answer to how it works is: It doesn't. So the cleanest approach would be to initialize the cntvoff when creating the VM, then enabling it at first vcpu run, adding a comment saying that enabling the timer multiple times doesn't hurt. Consequently adding a kvm_timer_enable() function that gets called on first vcpu_run ? > > > > - return 0; > > + return; > > } > > Don't bother with the return ;-). > Right, pattern matching is my thing. ;) -Christoffer -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
