Re: [PATCH v2 07/25] KVM: VMX: Set intercept for FRED MSRs

[Sean Christopherson <seanjc@google.com>]

On Fri, Sep 27, 2024, Xin Li wrote:
> > > > When FRED is advertised to a guest, KVM should allow FRED SSP MSRs
> > > > accesses through disabling FRED SSP MSRs interception no matter whether
> > > > supervisor shadow stacks are enabled or not.
> > > 
> > > KVM doesn't necessarily need to disabling MSR interception, e.g. if
> > > the expectation
> > > is that the guest will rarely/never access the MSRs when CET is
> > > unsupported, then
> > > we're likely better off going with a trap-and-emulate model.  KVM
> > > needs to emulate
> > > RDMSR and WRMSR no matter what, e.g. in case the guest triggers a
> > > WRMSR when KVM
> > > is emulating, and so that userspace can get/set MSR values.
> > > 
> > > And this means that yes, FRED virtualization needs to land after CET
> > > virtualization,
> > > otherwise managing the conflicts/dependencies will be a nightmare.
> > > 
> 
> I still plan to send another iteration of the FRED patch set for review,
> however I haven't seen your x86 KVM changes land into Linus' tree, it
> will happen soon, right?

Yep, we squeaked into rc1, the pull request to Linus was delayed because of
travel and conferences.