linux-kernel - Re: [PATCH v2 05/21] KVM: x86: Disallow writes to immutable feature MSRs after KVM

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Message-ID: <Y+ZxXJa0nMIg/f32@google.com>
Date:   Fri, 10 Feb 2023 16:31:24 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Yu Zhang <yu.c.zhang@...ux.intel.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Xiaoyao Li <xiaoyao.li@...el.com>,
        Like Xu <like.xu.linux@...il.com>
Subject: Re: [PATCH v2 05/21] KVM: x86: Disallow writes to immutable feature
 MSRs after KVM_RUN

On Fri, Feb 10, 2023, Yu Zhang wrote:
> On Fri, Feb 10, 2023 at 12:31:32AM +0000, Sean Christopherson wrote:
> > @@ -2168,6 +2187,23 @@ static int do_get_msr(struct kvm_vcpu *vcpu, unsigned index, u64 *data)
> >  
> >  static int do_set_msr(struct kvm_vcpu *vcpu, unsigned index, u64 *data)
> >  {
> > +	u64 val;
> > +
> > +	/*
> > +	 * Disallow writes to immutable feature MSRs after KVM_RUN.  KVM does
> > +	 * not support modifying the guest vCPU model on the fly, e.g. changing
> > +	 * the nVMX capabilities while L2 is running is nonsensical.  Ignore
> > +	 * writes of the same value, e.g. to allow userspace to blindly stuff
> > +	 * all MSRs when emulating RESET.
> > +	 */
> > +	if (vcpu->arch.last_vmentry_cpu != -1 &&
> 
> Use kvm_vcpu_has_run(vcpu) here? 

/facepalm

Yes, that was the entire point of adding the helper.

Thanks!