linux-kernel - Re: [PATCH v4 13/20] KVM:VMX: Emulate read and write to CET MSRs

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Message-ID: <ZMDT/r4sEfMj5Bmu@chao-email>
Date:   Wed, 26 Jul 2023 16:06:22 +0800
From:   Chao Gao <chao.gao@...el.com>
To:     Yang Weijiang <weijiang.yang@...el.com>
CC:     <seanjc@...gle.com>, <pbonzini@...hat.com>, <peterz@...radead.org>,
        <john.allen@....com>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <rick.p.edgecombe@...el.com>,
        <binbin.wu@...ux.intel.com>
Subject: Re: [PATCH v4 13/20] KVM:VMX: Emulate read and write to CET MSRs

On Thu, Jul 20, 2023 at 11:03:45PM -0400, Yang Weijiang wrote:
>Add VMX specific emulation for CET MSR read and write.
>IBT feature is only available on Intel platforms now and the
>virtualization interface to the control fields is vensor
>specific, so split this part from the common code.
>
>Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
>---
> arch/x86/kvm/vmx/vmx.c | 40 ++++++++++++++++++++++++++++++++++++++++
> arch/x86/kvm/x86.c     |  7 -------
> 2 files changed, 40 insertions(+), 7 deletions(-)
>
>diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
>index c8d9870cfecb..b29817ec6f2e 100644
>--- a/arch/x86/kvm/vmx/vmx.c
>+++ b/arch/x86/kvm/vmx/vmx.c
>@@ -2093,6 +2093,21 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> 		else
> 			msr_info->data = vmx->pt_desc.guest.addr_a[index / 2];
> 		break;
>+	case MSR_IA32_U_CET:
>+	case MSR_IA32_PL0_SSP ... MSR_IA32_PL3_SSP:
>+		return kvm_get_msr_common(vcpu, msr_info);

kvm_get_msr_common() is called for the "default" case. so this can be dropped.

>+	case MSR_IA32_S_CET:
>+	case MSR_KVM_GUEST_SSP:
>+	case MSR_IA32_INT_SSP_TAB:
>+		if (kvm_get_msr_common(vcpu, msr_info))
>+			return 1;
>+		if (msr_info->index == MSR_KVM_GUEST_SSP)
>+			msr_info->data = vmcs_readl(GUEST_SSP);
>+		else if (msr_info->index == MSR_IA32_S_CET)
>+			msr_info->data = vmcs_readl(GUEST_S_CET);
>+		else if (msr_info->index == MSR_IA32_INT_SSP_TAB)
>+			msr_info->data = vmcs_readl(GUEST_INTR_SSP_TABLE);
>+		break;
> 	case MSR_IA32_DEBUGCTLMSR:
> 		msr_info->data = vmcs_read64(GUEST_IA32_DEBUGCTL);
> 		break;
>@@ -2402,6 +2417,31 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> 		else
> 			vmx->pt_desc.guest.addr_a[index / 2] = data;
> 		break;
>+#define VMX_CET_CONTROL_MASK		(~GENMASK_ULL(9, 6))

bits9-6 are reserved for both intel and amd. Shouldn't this check be
done in the common code?

>+#define CET_LEG_BITMAP_BASE(data)	((data) >> 12)
>+#define CET_EXCLUSIVE_BITS		(CET_SUPPRESS | CET_WAIT_ENDBR)

>+	case MSR_IA32_PL0_SSP ... MSR_IA32_PL3_SSP:
>+		return kvm_set_msr_common(vcpu, msr_info);

this hunk can be dropped as well.

>+		break;
>+	case MSR_IA32_U_CET:
>+	case MSR_IA32_S_CET:
>+	case MSR_KVM_GUEST_SSP:
>+	case MSR_IA32_INT_SSP_TAB:
>+		if ((msr_index == MSR_IA32_U_CET ||
>+		     msr_index == MSR_IA32_S_CET) &&
>+		    ((data & ~VMX_CET_CONTROL_MASK) ||
>+		     !IS_ALIGNED(CET_LEG_BITMAP_BASE(data), 4) ||
>+		     (data & CET_EXCLUSIVE_BITS) == CET_EXCLUSIVE_BITS))
>+			return 1;

how about

	case MSR_IA32_U_CET:
	case MSR_IA32_S_CET:
		if ((data & ~VMX_CET_CONTROL_MASK) || ...
			...

	case MSR_KVM_GUEST_SSP:
	case MSR_IA32_INT_SSP_TAB: