[PATCH] KVM: nVMX: Rebuild MSR bitmap after eVMCS control changes

[PATCH] KVM: nVMX: Rebuild MSR bitmap after eVMCS control changes

[Weiming Shi]

The Enlightened MSR Bitmap shortcut reuses vmcs02's bitmap when L1 marks
MSR_BITMAP clean, but the bitmap also depends on execution controls in
CONTROL_GRP1 and CONTROL_PROC.  L1 can change either group while leaving
MSR_BITMAP clean, preserving stale APIC_TASKPRI passthrough for L2.

Reusing the bitmap after a failed rebuild is unsafe too.  The failed entry
disables hardware MSR bitmaps, but KVM subsequently marks the eVMCS clean,
allowing the next entry to reactivate the old vmcs02 bitmap.

Require both control groups to be clean before reusing the bitmap, and keep
force_msr_bitmap_recalc set until a rebuild succeeds.

Fixes: 502d2bf5f2fd ("KVM: nVMX: Implement Enlightened MSR Bitmap feature")
Cc: stable@vger.kernel.org
Reported-by: Zhong Wang <wangzhong.c0ss4ck@bytedance.com>
Assisted-by: LLM
Signed-off-by: Weiming Shi <bestswngs@gmail.com>
---
 arch/x86/kvm/vmx/nested.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 151873407abd3..0f0e677d99482 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -755,13 +755,17 @@ static inline bool nested_vmx_prepare_msr_bitmap(struct kvm_vcpu *vcpu,
 		struct hv_enlightened_vmcs *evmcs = nested_vmx_evmcs(vmx);
 
 		if (evmcs && evmcs->hv_enlightenments_control.msr_bitmap &&
-		    evmcs->hv_clean_fields & HV_VMX_ENLIGHTENED_CLEAN_FIELD_MSR_BITMAP)
+		    evmcs->hv_clean_fields & HV_VMX_ENLIGHTENED_CLEAN_FIELD_MSR_BITMAP &&
+		    evmcs->hv_clean_fields & HV_VMX_ENLIGHTENED_CLEAN_FIELD_CONTROL_GRP1 &&
+		    evmcs->hv_clean_fields & HV_VMX_ENLIGHTENED_CLEAN_FIELD_CONTROL_PROC)
 			return true;
 	}
 
 	CLASS(kvm_vcpu_map_local_readonly, m)(vcpu, gpa_to_gfn(vmcs12->msr_bitmap));
-	if (m.ret)
+	if (m.ret) {
+		vmx->nested.force_msr_bitmap_recalc = true;
 		return false;
+	}
 
 	msr_bitmap_l1 = (unsigned long *)m.map.hva;
 
-- 
2.55.0