linux-kernel - [PATCH v5 4/8] KVM: VMX: Pass through CET related MSRs to Guest

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Date:   Wed, 22 May 2019 15:00:57 +0800
From:   Yang Weijiang <weijiang.yang@...el.com>
To:     pbonzini@...hat.com, sean.j.christopherson@...el.com,
        mst@...hat.com, rkrcmar@...hat.com, jmattson@...gle.com,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        yu-cheng.yu@...el.com
Cc:     weijiang.yang@...el.com
Subject: [PATCH v5 4/8] KVM: VMX: Pass through CET related MSRs to Guest

CET MSRs pass through Guest directly to enhance performance.
CET runtime control settings are stored in MSR_IA32_{U,S}_CET,
Shadow Stack Pointer(SSP) are presented in MSR_IA32_PL{0,1,2,3}_SSP,
SSP table base address is stored in MSR_IA32_INT_SSP_TAB,
these MSRs are defined in kernel and re-used here.

MSR_IA32_U_CET and MSR_IA32_PL3_SSP are used for user mode protection,
the contents could differ from process to process, therefore,
kernel needs to save/restore them during context switch, so it makes
sense to pass through them so that the guest kernel can
use xsaves/xrstors to operate them efficiently. Ohter MSRs are used
for non-user mode protection. See CET spec for detailed info.

The difference between CET VMCS state fields and xsave components is,
the former used for CET state storage during VMEnter/VMExit,
whereas the latter used for state retention between Guest task/process
switch.

Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
Co-developed-by: Zhang Yi Z <yi.z.zhang@...ux.intel.com>
---
 arch/x86/kvm/vmx/vmx.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 574428375ff9..9321da538f65 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6942,6 +6942,7 @@ static void update_intel_pt_cfg(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);
@@ -6963,6 +6964,19 @@ static void vmx_cpuid_update(struct kvm_vcpu *vcpu)
 	if (boot_cpu_has(X86_FEATURE_INTEL_PT) &&
 			guest_cpuid_has(vcpu, X86_FEATURE_INTEL_PT))
 		update_intel_pt_cfg(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_PL1_SSP, MSR_TYPE_RW);
+		vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_PL2_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)
@@ -7163,6 +7177,7 @@ static void __pi_post_block(struct kvm_vcpu *vcpu)
 		spin_unlock(&per_cpu(blocked_vcpu_on_cpu_lock, vcpu->pre_pcpu));
 		vcpu->pre_pcpu = -1;
 	}
+
 }
 
 /*
-- 
2.17.2