Re: [PATCH v3 5/8] KVM:VMX: Pass through host CET related MSRs to Guest.

[Yang Weijiang]

On Mon, Mar 04, 2019 at 10:53:27AM -0800, Sean Christopherson wrote:
> On Mon, Feb 25, 2019 at 09:27:13PM +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.
> 
> But don't we want to allow a guest to access the MSRs regardless of
> the host kernel's behavior?
>
Do you see any necessity of exposing the access to guest?

> > Signed-off-by: Zhang Yi Z <yi.z.zhang@xxxxxxxxxxxxxxx>
> > Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
> > ---
> >  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 7bbb8b26e901..89ee086e1729 100644
> > --- a/arch/x86/kvm/vmx.c
> > +++ b/arch/x86/kvm/vmx.c
> > @@ -11769,6 +11769,7 @@ 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);
> > @@ -11786,6 +11787,18 @@ 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) |
> 
> This should be a logical OR, not a bitwise OR.
> 
Good capture, thanks!

> > +	    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);
> > +		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
> >