Re: [PATCH v3 1/3] KVM: nVMX: Sync L2 guest CET states between L1/L2

[Yang Weijiang <weijiang.yang@intel.com>]

On Thu, Mar 04, 2021 at 10:50:10AM +0100, Vitaly Kuznetsov wrote:
> Yang Weijiang <weijiang.yang@intel.com> writes:
> 
> > These fields are rarely updated by L1 QEMU/KVM, sync them when L1 is trying to
> > read/write them and after they're changed. If CET guest entry-load bit is not
> > set by L1 guest, migrate them to L2 manaully.
> >
> > Suggested-by: Sean Christopherson <seanjc@google.com>
> > Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
> > ---
> >  arch/x86/kvm/cpuid.c      |  1 -
> >  arch/x86/kvm/vmx/nested.c | 30 ++++++++++++++++++++++++++++++
> >  arch/x86/kvm/vmx/vmx.h    |  3 +++
> >  3 files changed, 33 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> > index d191de769093..8692f53b8cd0 100644
> > --- a/arch/x86/kvm/cpuid.c
> > +++ b/arch/x86/kvm/cpuid.c
> > @@ -143,7 +143,6 @@ void kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu)
> >  		}
> >  		vcpu->arch.guest_supported_xss =
> >  			(((u64)best->edx << 32) | best->ecx) & supported_xss;
> > -
> 
> Nitpick: stray change?

Yes, I should keep the change log in V2 :-)

> 
> >  	} else {
> >  		vcpu->arch.guest_supported_xss = 0;
> >  	}
> > diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> > index 9728efd529a1..24cace55e1f9 100644
> > --- a/arch/x86/kvm/vmx/nested.c
> > +++ b/arch/x86/kvm/vmx/nested.c
> > @@ -2516,6 +2516,13 @@ static void prepare_vmcs02_rare(struct vcpu_vmx *vmx, struct vmcs12 *vmcs12)
> >  	vmcs_write32(VM_ENTRY_MSR_LOAD_COUNT, vmx->msr_autoload.guest.nr);
> >  
> >  	set_cr4_guest_host_mask(vmx);
> > +
> > +	if (kvm_cet_supported() && vmx->nested.nested_run_pending &&
> > +	    (vmcs12->vm_entry_controls & VM_ENTRY_LOAD_CET_STATE)) {
> > +		vmcs_writel(GUEST_SSP, vmcs12->guest_ssp);
> > +		vmcs_writel(GUEST_S_CET, vmcs12->guest_s_cet);
> > +		vmcs_writel(GUEST_INTR_SSP_TABLE, vmcs12->guest_ssp_tbl);
> > +	}
> >  }
> >  
> >  /*
> > @@ -2556,6 +2563,15 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
> >  	if (kvm_mpx_supported() && (!vmx->nested.nested_run_pending ||
> >  	    !(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_BNDCFGS)))
> >  		vmcs_write64(GUEST_BNDCFGS, vmx->nested.vmcs01_guest_bndcfgs);
> > +
> > +	if (kvm_cet_supported() && (!vmx->nested.nested_run_pending ||
> > +	    !(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_CET_STATE))) {
> > +		vmcs_writel(GUEST_SSP, vmx->nested.vmcs01_guest_ssp);
> > +		vmcs_writel(GUEST_S_CET, vmx->nested.vmcs01_guest_s_cet);
> > +		vmcs_writel(GUEST_INTR_SSP_TABLE,
> > +			    vmx->nested.vmcs01_guest_ssp_tbl);
> > +	}
> > +
> >  	vmx_set_rflags(vcpu, vmcs12->guest_rflags);
> >  
> >  	/* EXCEPTION_BITMAP and CR0_GUEST_HOST_MASK should basically be the
> > @@ -3375,6 +3391,12 @@ enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu,
> >  	if (kvm_mpx_supported() &&
> >  		!(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_BNDCFGS))
> >  		vmx->nested.vmcs01_guest_bndcfgs = vmcs_read64(GUEST_BNDCFGS);
> > +	if (kvm_cet_supported() &&
> > +		!(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_CET_STATE)) {
> > +		vmx->nested.vmcs01_guest_ssp = vmcs_readl(GUEST_SSP);
> > +		vmx->nested.vmcs01_guest_s_cet = vmcs_readl(GUEST_S_CET);
> > +		vmx->nested.vmcs01_guest_ssp_tbl = vmcs_readl(GUEST_INTR_SSP_TABLE);
> > +	}
> >  
> >  	/*
> >  	 * Overwrite vmcs01.GUEST_CR3 with L1's CR3 if EPT is disabled *and*
> > @@ -4001,6 +4023,9 @@ static bool is_vmcs12_ext_field(unsigned long field)
> >  	case GUEST_IDTR_BASE:
> >  	case GUEST_PENDING_DBG_EXCEPTIONS:
> >  	case GUEST_BNDCFGS:
> > +	case GUEST_SSP:
> > +	case GUEST_INTR_SSP_TABLE:
> > +	case GUEST_S_CET:
> >  		return true;
> >  	default:
> >  		break;
> > @@ -4052,6 +4077,11 @@ static void sync_vmcs02_to_vmcs12_rare(struct kvm_vcpu *vcpu,
> >  		vmcs_readl(GUEST_PENDING_DBG_EXCEPTIONS);
> >  	if (kvm_mpx_supported())
> >  		vmcs12->guest_bndcfgs = vmcs_read64(GUEST_BNDCFGS);
> > +	if (kvm_cet_supported()) {
> > +		vmcs12->guest_ssp = vmcs_readl(GUEST_SSP);
> > +		vmcs12->guest_s_cet = vmcs_readl(GUEST_S_CET);
> > +		vmcs12->guest_ssp_tbl = vmcs_readl(GUEST_INTR_SSP_TABLE);
> > +	}
> >  
> >  	vmx->nested.need_sync_vmcs02_to_vmcs12_rare = false;
> >  }
> > diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
> > index 9d3a557949ac..36dc4fdb0909 100644
> > --- a/arch/x86/kvm/vmx/vmx.h
> > +++ b/arch/x86/kvm/vmx/vmx.h
> > @@ -155,6 +155,9 @@ struct nested_vmx {
> >  	/* to migrate it to L2 if VM_ENTRY_LOAD_DEBUG_CONTROLS is off */
> >  	u64 vmcs01_debugctl;
> >  	u64 vmcs01_guest_bndcfgs;
> > +	u64 vmcs01_guest_ssp;
> > +	u64 vmcs01_guest_s_cet;
> > +	u64 vmcs01_guest_ssp_tbl;
> >  
> >  	/* to migrate it to L1 if L2 writes to L1's CR8 directly */
> >  	int l1_tpr_threshold;
> 
> -- 
> Vitaly