linux-kernel - [RFC PATCH v4 4/8] KVM:VMX: Pass through host CET related MSRs to Guest.

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Date:   Mon, 18 Mar 2019 23:03:47 +0800
From:   Yang Weijiang <weijiang.yang@...el.com>
To:     pbonzini@...hat.com, kvm@...r.kernel.org, mst@...hat.com,
        rkrcmar@...hat.com, jmattson@...gle.com,
        linux-kernel@...r.kernel.org, yu-cheng.yu@...el.com
Cc:     Yang Weijiang <weijiang.yang@...el.com>,
        Zhang Yi Z <yi.z.zhang@...ux.intel.com>
Subject: [RFC PATCH v4 4/8] KVM:VMX: Pass through host CET related MSRs to Guest.

The CET runtime settings, i.e., CET state control bits(IA32_U_CET/
IA32_S_CET), CET SSP(IA32_PL3_SSP/IA32_PL0_SSP) and SSP table address
(IA32_INTERRUPT_SSP_TABLE_ADDR) are task/thread specific, therefore,
OS needs to save/restore the states properly during context switch,
e.g., task/thread switching, interrupt/exception handling, it uses
xsaves/xrstors to achieve that.

The difference between VMCS CET area fields and xsave CET area, is that
the former is for state retention during Guest/Host context
switch while the latter is for state retention during OS execution.

Linux currently doesn't support CPL1 and CPL2, so SSPs for these level
are skipped here.

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 | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 53cef5a3db96..28b8ac027bd7 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -11774,6 +11774,7 @@ static void nested_vmx_entry_exit_ctls_update(struct kvm_vcpu *vcpu)
 static void vmx_cpuid_update(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
+	unsigned long *msr_bitmap;
 
 	if (cpu_has_secondary_exec_ctrls()) {
 		vmx_compute_secondary_exec_control(vmx);
@@ -11791,6 +11792,18 @@ static void vmx_cpuid_update(struct kvm_vcpu *vcpu)
 		nested_vmx_cr_fixed1_bits_update(vcpu);
 		nested_vmx_entry_exit_ctls_update(vcpu);
 	}
+
+	msr_bitmap = vmx->vmcs01.msr_bitmap;
+
+	if (guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) ||
+	    guest_cpuid_has(vcpu, X86_FEATURE_IBT)) {
+		vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_U_CET, MSR_TYPE_RW);
+		vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_S_CET, MSR_TYPE_RW);
+		vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_INT_SSP_TAB, MSR_TYPE_RW);
+		vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_PL0_SSP, MSR_TYPE_RW);
+		vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_PL3_SSP, MSR_TYPE_RW);
+	}
+
 }
 
 static void vmx_set_supported_cpuid(u32 func, struct kvm_cpuid_entry2 *entry)
-- 
2.17.1