linux-kernel - Re: [RFC PATCH v4 4/8] KVM:VMX: Pass through host CET related MSRs to Guest.

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Date:   Wed, 3 Apr 2019 04:46:21 +0800
From:   Yang Weijiang <weijiang.yang@...el.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     pbonzini@...hat.com, kvm@...r.kernel.org, mst@...hat.com,
        rkrcmar@...hat.com, jmattson@...gle.com,
        linux-kernel@...r.kernel.org, yu-cheng.yu@...el.com,
        Zhang Yi Z <yi.z.zhang@...ux.intel.com>
Subject: Re: [RFC PATCH v4 4/8] KVM:VMX: Pass through host CET related MSRs
 to Guest.

On Tue, Apr 02, 2019 at 01:27:33PM -0700, Sean Christopherson wrote:
> On Mon, Mar 18, 2019 at 11:03:47PM +0800, Yang Weijiang wrote:
> > The CET runtime settings, i.e., CET state control bits(IA32_U_CET/
> > IA32_S_CET), CET SSP(IA32_PL3_SSP/IA32_PL0_SSP) and SSP table address
> > (IA32_INTERRUPT_SSP_TABLE_ADDR) are task/thread specific, therefore,
> > OS needs to save/restore the states properly during context switch,
> > e.g., task/thread switching, interrupt/exception handling, it uses
> > xsaves/xrstors to achieve that.
> > 
> > The difference between VMCS CET area fields and xsave CET area, is that
> > the former is for state retention during Guest/Host context
> > switch while the latter is for state retention during OS execution.
> > 
> > Linux currently doesn't support CPL1 and CPL2, so SSPs for these level
> > are skipped here.
> > 
> > Signed-off-by: Zhang Yi Z <yi.z.zhang@...ux.intel.com>
> > Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
> > ---
> >  arch/x86/kvm/vmx.c | 13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> > 
> > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> > index 53cef5a3db96..28b8ac027bd7 100644
> > --- a/arch/x86/kvm/vmx.c
> > +++ b/arch/x86/kvm/vmx.c
> > @@ -11774,6 +11774,7 @@ static void nested_vmx_entry_exit_ctls_update(struct kvm_vcpu *vcpu)
> >  static void vmx_cpuid_update(struct kvm_vcpu *vcpu)
> >  {
> >  	struct vcpu_vmx *vmx = to_vmx(vcpu);
> > +	unsigned long *msr_bitmap;
> >  
> >  	if (cpu_has_secondary_exec_ctrls()) {
> >  		vmx_compute_secondary_exec_control(vmx);
> > @@ -11791,6 +11792,18 @@ static void vmx_cpuid_update(struct kvm_vcpu *vcpu)
> >  		nested_vmx_cr_fixed1_bits_update(vcpu);
> >  		nested_vmx_entry_exit_ctls_update(vcpu);
> >  	}
> > +
> > +	msr_bitmap = vmx->vmcs01.msr_bitmap;
> > +
> > +	if (guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) ||
> > +	    guest_cpuid_has(vcpu, X86_FEATURE_IBT)) {
> > +		vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_U_CET, MSR_TYPE_RW);
> > +		vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_S_CET, MSR_TYPE_RW);
> > +		vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_INT_SSP_TAB, MSR_TYPE_RW);
> > +		vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_PL0_SSP, MSR_TYPE_RW);
> 
> I thought we had agreed to pass-through PL1 and PL2, or am I misremembering?
>
Thanks Sean! I missed your last comments on this patch, will add them in
next version.
> > +		vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_PL3_SSP, MSR_TYPE_RW);
> > +	}
> > +
> >  }
> >  
> >  static void vmx_set_supported_cpuid(u32 func, struct kvm_cpuid_entry2 *entry)
> > -- 
> > 2.17.1
> >