Re: [RFC PATCH v3 03/27] x86/kvm: Disable PV_SEND_IPI if Secure AVIC is enabled

[Tom Lendacky]

On 7/8/26 01:32, Naveen N Rao (AMD) wrote:
> In Secure AVIC mode, Linux does not allow IPIs to be injected as the
> hypervisor is untrusted. This is achieved by not setting the IPI vector
> in SAVIC_ALLOWED_IRR in the Secure AVIC guest APIC Backing page. Due to
> this, PV_SEND_IPI cannot work since it needs KVM to be able to inject
> IPIs into the guest. Disable the same.

Another guest patch...

Does this have an impact on the hypervisor? Is the injected IPI just
ignored because of the SAVIC_ALLOWED_IRR? How would the hypervisor know
that it needs to schedule the target vCPU if not using this, a write to
the ICR?

Thanks,
Tom

> 
> On a related note, PV_EOI does not need to be disabled since the
> behavior is exactly the same as AVIC: though it is advertised, KVM never
> "enables" it since APICv is always enabled for Secure AVIC SEV-SNP
> guests.
> 
> Fixes: c4074ab87f34 ("x86/apic: Enable Secure AVIC in the control MSR")
> Signed-off-by: Naveen N Rao (AMD) <naveen@xxxxxxxxxx>
> ---
>  arch/x86/kernel/kvm.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index 29226d112029..e2dad507f2a4 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -495,7 +495,8 @@ static bool pv_tlb_flush_supported(void)
>  static bool pv_ipi_supported(void)
>  {
>  	return (kvm_para_has_feature(KVM_FEATURE_PV_SEND_IPI) &&
> -	       (num_possible_cpus() != 1));
> +		(num_possible_cpus() != 1) &&
> +		!cc_platform_has(CC_ATTR_SNP_SECURE_AVIC));
>  }
>  
>  static bool pv_sched_yield_supported(void)