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

Marc Zyngier
2017-01-05T17:40:58Z

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?

> +
> 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,

M.
--
Jazz is not dead. It just smells funny...