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

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Message-ID: <ZvrYOj0Nn9m8VIWV@google.com>
Date: Mon, 30 Sep 2024 09:56:26 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Xin Li <xin@...or.com>
Cc: Chao Gao <chao.gao@...el.com>, Xin Li <xin3.li@...el.com>, linux-kernel@...r.kernel.org, 
	kvm@...r.kernel.org, linux-doc@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, pbonzini@...hat.com, corbet@....net, 
	tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, 
	dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com, shuah@...nel.org, 
	vkuznets@...hat.com, peterz@...radead.org, ravi.v.shankar@...el.com
Subject: Re: [PATCH v2 07/25] KVM: VMX: Set intercept for FRED MSRs

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.