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 <christoffer.dall@xxxxxxxxxx> 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 <christoffer.dall@xxxxxxxxxx>
> > ---
> > 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
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