[PATCH 3/3] KVM: VMX: simplify MSR interception enable/disable

[Dongli Zhang]

Currently, the is_valid_passthrough_msr() is only called by two sites:
vmx_enable_intercept_for_msr() and vmx_disable_intercept_for_msr(). The
is_valid_passthrough_msr() is called for two reasons.

1. Do WARN() if the input msr is neither x2APIC/PT/LBR passthrough MSRs,
nor the possible passthrough MSRs.

2. Return if the msr is a possible passthrough MSR.

While the is_valid_passthrough_msr() may traverse the
vmx_possible_passthrough_msrs[], the following
possible_passthrough_msr_slot() may traverse the save array again. There
is no need to call possible_passthrough_msr_slot() twice.

vmx_disable_intercept_for_msr()
-> is_valid_passthrough_msr()
   -> possible_passthrough_msr_slot()
-> possible_passthrough_msr_slot()

Therefore, we merge the is_valid_passthrough_msr() and the following
possible_passthrough_msr_slot() into the same function:

- If the msr is not any passthrough MSR, WARN and return -ENOENT.
- Return VMX_OTHER_PASSTHROUGH if x2apic/PT/LBR.
- Return VMX_POSSIBLE_PASSTHROUGH and set possible_idx, if possible
passthrough MSRs.

Signed-off-by: Dongli Zhang <dongli.zhang@xxxxxxxxxx>
---
 arch/x86/kvm/vmx/vmx.c | 55 +++++++++++++++++++++---------------------
 1 file changed, 28 insertions(+), 27 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 5a866d3c2bc8..76dff0e7d8bd 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -669,14 +669,18 @@ static int possible_passthrough_msr_slot(u32 msr)
 	return -ENOENT;
 }
 
-static bool is_valid_passthrough_msr(u32 msr)
+#define VMX_POSSIBLE_PASSTHROUGH	1
+#define VMX_OTHER_PASSTHROUGH		2
+/*
+ * Vefify if the msr is the passthrough MSRs.
+ * Return the index in *possible_idx if it is a possible passthrough MSR.
+ */
+static int validate_passthrough_msr(u32 msr, int *possible_idx)
 {
-	bool r;
-
 	switch (msr) {
 	case 0x800 ... 0x8ff:
 		/* x2APIC MSRs. These are handled in vmx_update_msr_bitmap_x2apic() */
-		return true;
+		return VMX_OTHER_PASSTHROUGH;
 	case MSR_IA32_RTIT_STATUS:
 	case MSR_IA32_RTIT_OUTPUT_BASE:
 	case MSR_IA32_RTIT_OUTPUT_MASK:
@@ -691,14 +695,17 @@ static bool is_valid_passthrough_msr(u32 msr)
 	case MSR_LBR_CORE_FROM ... MSR_LBR_CORE_FROM + 8:
 	case MSR_LBR_CORE_TO ... MSR_LBR_CORE_TO + 8:
 		/* LBR MSRs. These are handled in vmx_update_intercept_for_lbr_msrs() */
-		return true;
+		return VMX_OTHER_PASSTHROUGH;
 	}
 
-	r = possible_passthrough_msr_slot(msr) != -ENOENT;
+	*possible_idx = possible_passthrough_msr_slot(msr);
+	WARN(*possible_idx == -ENOENT,
+	     "Invalid MSR %x, please adapt vmx_possible_passthrough_msrs[]", msr);
 
-	WARN(!r, "Invalid MSR %x, please adapt vmx_possible_passthrough_msrs[]", msr);
+	if (*possible_idx >= 0)
+		return VMX_POSSIBLE_PASSTHROUGH;
 
-	return r;
+	return -ENOENT;
 }
 
 struct vmx_uret_msr *vmx_find_uret_msr(struct vcpu_vmx *vmx, u32 msr)
@@ -3954,6 +3961,7 @@ void vmx_disable_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, int type)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	unsigned long *msr_bitmap = vmx->vmcs01.msr_bitmap;
+	int idx;
 
 	if (!cpu_has_vmx_msr_bitmap())
 		return;
@@ -3963,16 +3971,12 @@ void vmx_disable_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, int type)
 	/*
 	 * 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);
-
-		if (idx != -ENOENT) {
-			if (type & MSR_TYPE_R)
-				clear_bit(idx, vmx->shadow_msr_intercept.read);
-			if (type & MSR_TYPE_W)
-				clear_bit(idx, vmx->shadow_msr_intercept.write);
-		}
+	 */
+	if (validate_passthrough_msr(msr, &idx) == VMX_POSSIBLE_PASSTHROUGH) {
+		if (type & MSR_TYPE_R)
+			clear_bit(idx, vmx->shadow_msr_intercept.read);
+		if (type & MSR_TYPE_W)
+			clear_bit(idx, vmx->shadow_msr_intercept.write);
 	}
 
 	if ((type & MSR_TYPE_R) &&
@@ -3998,6 +4002,7 @@ void vmx_enable_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, int type)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	unsigned long *msr_bitmap = vmx->vmcs01.msr_bitmap;
+	int idx;
 
 	if (!cpu_has_vmx_msr_bitmap())
 		return;
@@ -4008,15 +4013,11 @@ void vmx_enable_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, int type)
 	 * Mark the desired intercept state in shadow bitmap, this is needed
 	 * for resync when the MSR filter changes.
 	*/
-	if (is_valid_passthrough_msr(msr)) {
-		int idx = possible_passthrough_msr_slot(msr);
-
-		if (idx != -ENOENT) {
-			if (type & MSR_TYPE_R)
-				set_bit(idx, vmx->shadow_msr_intercept.read);
-			if (type & MSR_TYPE_W)
-				set_bit(idx, vmx->shadow_msr_intercept.write);
-		}
+	if (validate_passthrough_msr(msr, &idx) == VMX_POSSIBLE_PASSTHROUGH) {
+		if (type & MSR_TYPE_R)
+			set_bit(idx, vmx->shadow_msr_intercept.read);
+		if (type & MSR_TYPE_W)
+			set_bit(idx, vmx->shadow_msr_intercept.write);
 	}
 
 	if (type & MSR_TYPE_R)
-- 
2.34.1