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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Message-Id: <9307C088-C8F8-4587-ABB4-3CADF2CC3117@oracle.com>
Date:   Wed, 26 Dec 2018 10:52:38 +0200
From:   Liran Alon <liran.alon@...cle.com>
To:     Yang Weijiang <weijiang.yang@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, rkrcmar@...hat.com,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org, mst@...hat.com,
        yu-cheng.yu@...el.com, yi.z.zhang@...el.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 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