On Tue, 2022-04-12 at 06:58 -0500, Suravee Suthikulpanit wrote:
> When launching a VM with x2APIC and specify more than 255 vCPUs,
> the guest kernel can disable x2APIC (e.g. specify nox2apic kernel option).
> The VM fallbacks to xAPIC mode, and disable the vCPU ID 255.
>
> In this case, APICV should be disabled for the vCPU ID 255.
> Therefore, the APICV mode consisency check is no longer valid.
>
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
> ---
> arch/x86/kvm/x86.c | 13 +++++--------
> 1 file changed, 5 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 0c0ca599a353..d0fac57e9996 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -9765,6 +9765,11 @@ void kvm_vcpu_update_apicv(struct kvm_vcpu *vcpu)
> down_read(&vcpu->kvm->arch.apicv_update_lock);
>
> activate = kvm_apicv_activated(vcpu->kvm);
> +
> + /* Do not activate AVIC when APIC is disabled */
> + if (kvm_get_apic_mode(vcpu) == LAPIC_MODE_DISABLED)
> + activate = false;
> +
> if (vcpu->arch.apicv_active == activate)
> goto out;
>
> @@ -10159,14 +10164,6 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
> guest_timing_enter_irqoff();
>
> for (;;) {
> - /*
> - * Assert that vCPU vs. VM APICv state is consistent. An APICv
> - * update must kick and wait for all vCPUs before toggling the
> - * per-VM state, and responsing vCPUs must wait for the update
> - * to complete before servicing KVM_REQ_APICV_UPDATE.
> - */
> - WARN_ON_ONCE(kvm_apicv_activated(vcpu->kvm) != kvm_vcpu_apicv_active(vcpu));
> -
> exit_fastpath = static_call(kvm_x86_vcpu_run)(vcpu);
> if (likely(exit_fastpath != EXIT_FASTPATH_REENTER_GUEST))
> break;
That warning catches bugs, please don't remove it.
It can be made conditional on this vCPU having APIC enabled instead.
Best regards,
Maxim Levitsky
