[PATCH v3 3/6] KVM: nVMX: Add a quirk for KVM tweaks to VMX control MSRs

[Oliver Upton <oupton@google.com>]

KVM really has no business messing with the vCPU state. Nonetheless, it
has become ABI for KVM to adjust certain bits of the VMX entry/exit
control MSRs depending on the guest CPUID. Namely, the bits associated
with the IA32_PERF_GLOBAL_CTRL and IA32_BNDCFGS MSRs were conditionally
enabled if the guest CPUID allows for it.

Allow userspace to opt-out of changes to VMX control MSRs by adding a
new KVM quirk.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Oliver Upton <oupton@google.com>
---
 arch/x86/include/uapi/asm/kvm.h | 11 ++++++-----
 arch/x86/kvm/vmx/nested.c       |  3 +++
 arch/x86/kvm/vmx/vmx.c          |  3 +++
 3 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
index bf6e96011dfe..acbab6a97fae 100644
--- a/arch/x86/include/uapi/asm/kvm.h
+++ b/arch/x86/include/uapi/asm/kvm.h
@@ -428,11 +428,12 @@ struct kvm_sync_regs {
 	struct kvm_vcpu_events events;
 };
 
-#define KVM_X86_QUIRK_LINT0_REENABLED	   (1 << 0)
-#define KVM_X86_QUIRK_CD_NW_CLEARED	   (1 << 1)
-#define KVM_X86_QUIRK_LAPIC_MMIO_HOLE	   (1 << 2)
-#define KVM_X86_QUIRK_OUT_7E_INC_RIP	   (1 << 3)
-#define KVM_X86_QUIRK_MISC_ENABLE_NO_MWAIT (1 << 4)
+#define KVM_X86_QUIRK_LINT0_REENABLED		(1 << 0)
+#define KVM_X86_QUIRK_CD_NW_CLEARED		(1 << 1)
+#define KVM_X86_QUIRK_LAPIC_MMIO_HOLE		(1 << 2)
+#define KVM_X86_QUIRK_OUT_7E_INC_RIP		(1 << 3)
+#define KVM_X86_QUIRK_MISC_ENABLE_NO_MWAIT	(1 << 4)
+#define KVM_X86_QUIRK_TWEAK_VMX_CTRL_MSRS	(1 << 5)
 
 #define KVM_STATE_NESTED_FORMAT_VMX	0
 #define KVM_STATE_NESTED_FORMAT_SVM	1
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 59164394569f..3b22b1072eff 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -4813,6 +4813,9 @@ void nested_vmx_pmu_entry_exit_ctls_update(struct kvm_vcpu *vcpu)
 	if (!nested_vmx_allowed(vcpu))
 		return;
 
+	if (!kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_TWEAK_VMX_CTRL_MSRS))
+		return;
+
 	vmx = to_vmx(vcpu);
 	if (kvm_x86_ops.pmu_ops->is_valid_msr(vcpu, MSR_CORE_PERF_GLOBAL_CTRL)) {
 		vmx->nested.msrs.entry_ctls_high |=
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 77d74cbc2709..050820d931fe 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7246,6 +7246,9 @@ void nested_vmx_entry_exit_ctls_update(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 
+	if (!kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_TWEAK_VMX_CTRL_MSRS))
+		return;
+
 	if (kvm_mpx_supported()) {
 		bool mpx_enabled = guest_cpuid_has(vcpu, X86_FEATURE_MPX);
 
-- 
2.35.1.574.g5d30c73bfb-goog