linux-kernel - Re: [PATCH 16/28] KVM: VMX: Manually recalc all MSR intercepts on userspace MSR filter change

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Message-ID: <aD3bGxdrrplf0YvT@google.com>
Date: Mon, 2 Jun 2025 10:10:51 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Xin Li <xin@...or.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Borislav Petkov <bp@...en8.de>, Chao Gao <chao.gao@...el.com>, 
	Dapeng Mi <dapeng1.mi@...ux.intel.com>
Subject: Re: [PATCH 16/28] KVM: VMX: Manually recalc all MSR intercepts on
 userspace MSR filter change

On Fri, May 30, 2025, Xin Li wrote:
> > +
> > +	if (vcpu->arch.xfd_no_write_intercept)
> > +		vmx_disable_intercept_for_msr(vcpu, MSR_IA32_XFD, MSR_TYPE_RW);
> > +
> > +
> > +	vmx_set_intercept_for_msr(vcpu, MSR_IA32_SPEC_CTRL, MSR_TYPE_RW,
> > +				  !to_vmx(vcpu)->spec_ctrl);
> > +
> > +	if (kvm_cpu_cap_has(X86_FEATURE_XFD))
> > +		vmx_set_intercept_for_msr(vcpu, MSR_IA32_XFD_ERR, MSR_TYPE_R,
> > +					  !guest_cpu_cap_has(vcpu, X86_FEATURE_XFD));
> > +
> > +	if (boot_cpu_has(X86_FEATURE_IBPB))
> 
> I think Boris prefers using cpu_feature_enabled() instead — maybe this
> is a good opportunity to update this occurrence?

Yeah, I'm comfortable squeezing in that change.

> > +		vmx_set_intercept_for_msr(vcpu, MSR_IA32_PRED_CMD, MSR_TYPE_W,
> > +					  !guest_has_pred_cmd_msr(vcpu));
> > +
> > +	if (boot_cpu_has(X86_FEATURE_FLUSH_L1D))
> 
> Ditto.
> 
> > +		vmx_set_intercept_for_msr(vcpu, MSR_IA32_FLUSH_CMD, MSR_TYPE_W,
> > +					  !guest_cpu_cap_has(vcpu, X86_FEATURE_FLUSH_L1D));
> > +
> > +	/*
> > +	 * x2APIC and LBR MSR intercepts are modified on-demand and cannot be
> > +	 * filtered by userspace.
> > +	 */
> > +}