[PATCH 05/15] KVM: VMX: Add document to state that write to uret msr should always be intercepted

[Lai Jiangshan]

From: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>

And adds a corresponding sanity check code.

Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>
---
 arch/x86/kvm/vmx/vmx.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index e8a41fdc3c4d..cd081219b668 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -3703,13 +3703,21 @@ void vmx_disable_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, int type)
 	if (!cpu_has_vmx_msr_bitmap())
 		return;
 
+	/*
+	 * Write to uret msr should always be intercepted due to the mechanism
+	 * must know the current value.  Santity check to avoid any inadvertent
+	 * mistake in coding.
+	 */
+	if (WARN_ON_ONCE(vmx_find_uret_msr(vmx, msr) && (type & MSR_TYPE_W)))
+		return;
+
 	if (static_branch_unlikely(&enable_evmcs))
 		evmcs_touch_msr_bitmap();
 
 	/*
 	 * Mark the desired intercept state in shadow bitmap, this is needed
 	 * for resync when the MSR filters change.
-	*/
+	 */
 	if (is_valid_passthrough_msr(msr)) {
 		int idx = possible_passthrough_msr_slot(msr);
 
-- 
2.19.1.6.gb485710b