Re: [RFC PATCH 4/7] KVM: arm/arm64: Check that system supports split eoi/deactivate

Christoffer Dall
2017-01-06T10:02:57Z

On Thu, Jan 05, 2017 at 05:40:58PM +0000, Marc Zyngier wrote:
> On 10/12/16 20:47, Christoffer Dall wrote:
> > Some systems without proper firmware and/or hardware description data
> > don't support the split EOI and deactivate operation and therefore
> > don't provide an irq_set_vcpu_affinity implementation. On such
> > systems, we cannot leave the physical interrupt active after the timer
> > handler on the host has run, so we cannot support KVM with the timer
> > changes we about to introduce.
> >
> > Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
> > ---
> > virt/kvm/arm/arch_timer.c | 30 ++++++++++++++++++++++++++++++
> > 1 file changed, 30 insertions(+)
> >
> > diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c
> > index c7c3bfd..f27a086 100644
> > --- a/virt/kvm/arm/arch_timer.c
> > +++ b/virt/kvm/arm/arch_timer.c
> > @@ -418,6 +418,31 @@ static int kvm_timer_dying_cpu(unsigned int cpu)
> > return 0;
> > }
> >
> > +static bool has_split_eoi_deactivate_support(void)
> > +{
> > + struct irq_desc *desc;
> > + struct irq_data *data;
> > + struct irq_chip *chip;
> > +
> > + /*
> > + * Check if split EOI and deactivate is supported on this machine.
> > + */
> > + desc = irq_to_desc(host_vtimer_irq);
> > + if (!desc) {
> > + kvm_err("kvm_arch_timer: no host_vtimer_irq descriptor\n");
> > + return false;
> > + }
> > +
> > + data = irq_desc_get_irq_data(desc);
> > + chip = irq_data_get_irq_chip(data);
> > + if (!chip || !chip->irq_set_vcpu_affinity) {
> > + kvm_err("kvm_arch_timer: no split EOI/deactivate; abort\n");
> > + return false;
> > + }
> > +
> > + return true;
> > +}
>
> That feels really involved. How about reporting that we don't have a
> usable VGIC altogether from the GIC driver?
>

You mean not booting the kernel at all, or establish some communication
from the GIC driver to KVM, telling KVM if it's usable for
virtualization or not?

> > +
> > int kvm_timer_hyp_init(void)
> > {
> > struct arch_timer_kvm_info *info;
> > @@ -449,6 +474,11 @@ int kvm_timer_hyp_init(void)
> > return err;
> > }
> >
> > + if (!has_split_eoi_deactivate_support()) {
> > + disable_percpu_irq(host_vtimer_irq);
> > + return -ENODEV;
> > + }
> > +
> > kvm_info("virtual timer IRQ%d\n", host_vtimer_irq);
> >
> > cpuhp_setup_state(CPUHP_AP_KVM_ARM_TIMER_STARTING,
> >
>
Thanks,
-Christoffer