Re: [PATCH v3 17/62] KVM: SVM: Add enable_ipiv param, never set IsRunning if disabled

Naveen N Rao
2025-06-23T10:48:52Z

On Fri, Jun 20, 2025 at 07:39:16AM -0700, Sean Christopherson wrote:
> On Thu, Jun 19, 2025, Naveen N Rao wrote:
> > On Wed, Jun 11, 2025 at 03:45:20PM -0700, Sean Christopherson wrote:
> > > From: Maxim Levitsky <mlevitsk@redhat.com>
> > >
> > > Let userspace "disable" IPI virtualization for AVIC via the enable_ipiv
> > > module param, by never setting IsRunning. SVM doesn't provide a way to
> > > disable IPI virtualization in hardware, but by ensuring CPUs never see
> > > IsRunning=1, every IPI in the guest (except for self-IPIs) will generate a
> > > VM-Exit.
> >
> > I think this is good to have regardless of the erratum. Not sure about VMX,
> > but does it make sense to intercept writes to the self-ipi MSR as well?
>
> That doesn't work for AVIC, i.e. if the guest is MMIO to access the virtual APIC.

Right, I was thinking about the Self-IPI MSR, but the ICR will also need
to be intercepted.

>
> Regardless, I don't see any reason to manually intercept self-IPIs when IPI
> virtualization is disabled. AFAIK, there's no need to do so for correctness,
> and Intel's self-IPI virtualization isn't tied to IPI virtualization either.
> Self-IPI virtualization is enabled by virtual interrupt delivery, which in turn
> is enabled by KVM when enable_apicv is true:
>
> Self-IPI virtualization occurs only if the “virtual-interrupt delivery”
> VM-execution control is 1.

Excellent, for this patch:
Reviewed-by: Naveen N Rao (AMD) <naveen@kernel.org>

Thanks,
Naveen