[PATCH 2/4] KVM: nVMX: Don't change VM-{Entry,Exit} ctrl MSRs on MPX CPUID update

[Oliver Upton <oupton@google.com>]

KVM does not respect userspace's configuration of the "{load,clear}
IA32_BNDCFGS" bit in the IA32_VMX_TRUE_{ENTRY,EXIT}_CTLS MSRs, depending
on the order in which it sets the MSR and configures the guest's CPUID.
When the guest's CPUID is set, KVM will expose the "load IA32_BNDCFGS"
bits if MPX is exposed in the guest CPUID. In order to clear the bit,
userspace would need to write the VMX capability MSRs after updating
CPUID.

There are no ordering requirements on these ioctls. Fix the issue by
simply not updating the "{load,clear} IA32_BNDCFGS" bits on CPUID
update. Note that these bits are already exposed by default in the
respective VMX capability MSRs, if supported by hardware.

Fixes: 5f76f6f5ff96 ("KVM: nVMX: Do not expose MPX VMX controls when guest MPX disabled")
Signed-off-by: Oliver Upton <oupton@google.com>
---
 arch/x86/kvm/vmx/vmx.c | 21 +--------------------
 1 file changed, 1 insertion(+), 20 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index aca3ae2a02f3..8cf58ba60b01 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7227,23 +7227,6 @@ static void nested_vmx_cr_fixed1_bits_update(struct kvm_vcpu *vcpu)
 #undef cr4_fixed1_update
 }
 
-static void nested_vmx_entry_exit_ctls_update(struct kvm_vcpu *vcpu)
-{
-	struct vcpu_vmx *vmx = to_vmx(vcpu);
-
-	if (kvm_mpx_supported()) {
-		bool mpx_enabled = guest_cpuid_has(vcpu, X86_FEATURE_MPX);
-
-		if (mpx_enabled) {
-			vmx->nested.msrs.entry_ctls_high |= VM_ENTRY_LOAD_BNDCFGS;
-			vmx->nested.msrs.exit_ctls_high |= VM_EXIT_CLEAR_BNDCFGS;
-		} else {
-			vmx->nested.msrs.entry_ctls_high &= ~VM_ENTRY_LOAD_BNDCFGS;
-			vmx->nested.msrs.exit_ctls_high &= ~VM_EXIT_CLEAR_BNDCFGS;
-		}
-	}
-}
-
 static void update_intel_pt_cfg(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
@@ -7335,10 +7318,8 @@ static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 			~(FEAT_CTL_VMX_ENABLED_INSIDE_SMX |
 			  FEAT_CTL_VMX_ENABLED_OUTSIDE_SMX);
 
-	if (nested_vmx_allowed(vcpu)) {
+	if (nested_vmx_allowed(vcpu))
 		nested_vmx_cr_fixed1_bits_update(vcpu);
-		nested_vmx_entry_exit_ctls_update(vcpu);
-	}
 
 	if (boot_cpu_has(X86_FEATURE_INTEL_PT) &&
 			guest_cpuid_has(vcpu, X86_FEATURE_INTEL_PT))
-- 
2.35.0.rc2.247.g8bbb082509-goog