linux-kernel - Re: [PATCH v1 3/8] kvm:vmx Enable loading CET state bit while guest CR4.CET is being set.

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Date:   Thu, 27 Dec 2018 14:07:59 +0800
From:   "Yang,Weijiang" <weijiang.yang@...el.com>
To:     Liran Alon <liran.alon@...cle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "mst@...hat.com" <mst@...hat.com>,
        "Yu, Yu-cheng" <yu-cheng.yu@...el.com>,
        "Zhang, Yi Z" <yi.z.zhang@...el.com>,
        "hjl.tools@...il.com" <hjl.tools@...il.com>,
        Zhang Yi Z <yi.z.zhang@...ux.intel.com>
Subject: Re: [PATCH v1 3/8] kvm:vmx  Enable loading CET state bit while guest
 CR4.CET is being set.

On Wed, Dec 26, 2018 at 04:52:38PM +0800, Liran Alon wrote:

Thanks Liran for pointing out the issues!
I'll fix them in next version.
> 
> 
> > On 26 Dec 2018, at 10:15, Yang Weijiang <weijiang.yang@...el.com> wrote:
> > 
> > This bit controls whether guest CET states will be loaded on guest entry.
> > 
> > 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 | 19 +++++++++++++++++++
> > 1 file changed, 19 insertions(+)
> > 
> > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> > index 7bbb8b26e901..25fa6bd2fb95 100644
> > --- a/arch/x86/kvm/vmx.c
> > +++ b/arch/x86/kvm/vmx.c
> > @@ -1045,6 +1045,8 @@ struct vcpu_vmx {
> > 
> > 	bool req_immediate_exit;
> > 
> > +	bool vcpu_cet_on;
> > +
> > 	/* Support for PML */
> > #define PML_ENTITY_NUM		512
> > 	struct page *pml_pg;
> > @@ -5409,6 +5411,23 @@ static int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
> > 			return 1;
> > 	}
> > 
> > +	/*
> > +	 * When CET.CR4 is being set, it means we're enabling CET for
> 
> You probably meant to write here CR4.CET.
> 
> > +	 * the guest, then enable loading CET state bit in entry control.
> > +	 * Otherwise, clear loading CET bit to disable guest CET.
> > +	 */
> > +	if (cr4 & X86_CR4_CET) {
> > +		if (!to_vmx(vcpu)->vcpu_cet_on) {
> > +			vmcs_set_bits(VM_ENTRY_CONTROLS,
> > +				      VM_ENTRY_LOAD_GUEST_CET_STATE);
> > +			to_vmx(vcpu)->vcpu_cet_on = 1;
> > +		}
> > +	} else if (to_vmx(vcpu)->vcpu_cet_on) {
> > +		vmcs_clear_bits(VM_ENTRY_CONTROLS,
> > +				VM_ENTRY_LOAD_GUEST_CET_STATE);
> > +		to_vmx(vcpu)->vcpu_cet_on = 0;
> > +	}
> > +
> > 	if (to_vmx(vcpu)->nested.vmxon && !nested_cr4_valid(vcpu, cr4))
> > 		return 1;
> > 
> > -- 
> > 2.17.1
> > 
> 
> I haven’t seen a patch in the series that modifies kvm_set_cr4() to verify CR4.CET is not set when CET is not reported as supported by CPUID.
> I think that is missing from the series.
> 
> -Liran
> 
>