linux-kernel - Re: [PATCH v5 1/3] KVM: nVMX: Sync L2 guest CET states between L1/L2

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Date:   Wed, 21 Apr 2021 17:08:03 +0800
From:   Yang Weijiang <weijiang.yang@...el.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Yang Weijiang <weijiang.yang@...el.com>, pbonzini@...hat.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 1/3] KVM: nVMX: Sync L2 guest CET states between L1/L2

On Tue, Apr 20, 2021 at 05:35:01PM +0000, Sean Christopherson wrote:
> On Fri, Apr 09, 2021, Yang Weijiang wrote:
> > 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.
> > 
> > Opportunistically remove one blank line in previous patch.
> > 
> > Suggested-by: Sean Christopherson <seanjc@...gle.com>
> > Signed-off-by: Yang Weijiang <weijiang.yang@...el.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(-)
> > 
> >  	vmx_set_rflags(vcpu, vmcs12->guest_rflags);
> >  
> >  	/* EXCEPTION_BITMAP and CR0_GUEST_HOST_MASK should basically be the
> > @@ -3375,6 +3391,11 @@ 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() && !vmx->nested.nested_run_pending) {
> 
> This needs to be:
> 
> 	if (kvm_cet_supported() && (!vmx->nested.nested_run_pending ||
> 	    !(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_CET_STATE)))
> 
> otherwise the vmcs01_* members will be stale when emulating VM-Enter with
> vcmc12.vm_entry_controls.LOAD_CET_STATE=0.
> 
Thanks Sean! Change is included in v6 patch series.

> > +		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);
> > +	}