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

[Sean Christopherson <seanjc@google.com>]

On Fri, Feb 16, 2024, Dongli Zhang wrote:
> ---
>  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)

There's no need for a custom tri-state return value or an out-param, just return
the slot/-ENOENT.  Not fully tested yet, but this should do the trick.

From: Sean Christopherson <seanjc@google.com>
Date: Mon, 19 Feb 2024 07:58:10 -0800
Subject: [PATCH] KVM: VMX: Combine "check" and "get" APIs for passthrough MSR
 lookups

Combine possible_passthrough_msr_slot() and is_valid_passthrough_msr()
into a single function, vmx_get_passthrough_msr_slot(), and have the
combined helper return the slot on success, using a negative value to
indiciate "failure".

Combining the operations avoids iterating over the array of passthrough
MSRs twice for relevant MSRs.

Suggested-by: Dongli Zhang <dongli.zhang@oracle.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/vmx/vmx.c | 63 +++++++++++++++++-------------------------
 1 file changed, 25 insertions(+), 38 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 014cf47dc66b..969fd3aa0da3 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -658,25 +658,14 @@ static inline bool cpu_need_virtualize_apic_accesses(struct kvm_vcpu *vcpu)
 	return flexpriority_enabled && lapic_in_kernel(vcpu);
 }
 
-static int possible_passthrough_msr_slot(u32 msr)
+static int vmx_get_passthrough_msr_slot(u32 msr)
 {
-	u32 i;
-
-	for (i = 0; i < ARRAY_SIZE(vmx_possible_passthrough_msrs); i++)
-		if (vmx_possible_passthrough_msrs[i] == msr)
-			return i;
-
-	return -ENOENT;
-}
-
-static bool is_valid_passthrough_msr(u32 msr)
-{
-	bool r;
+	int i;
 
 	switch (msr) {
 	case 0x800 ... 0x8ff:
 		/* x2APIC MSRs. These are handled in vmx_update_msr_bitmap_x2apic() */
-		return true;
+		return -ENOENT;
 	case MSR_IA32_RTIT_STATUS:
 	case MSR_IA32_RTIT_OUTPUT_BASE:
 	case MSR_IA32_RTIT_OUTPUT_MASK:
@@ -691,14 +680,16 @@ 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 -ENOENT;
 	}
 
-	r = possible_passthrough_msr_slot(msr) != -ENOENT;
-
-	WARN(!r, "Invalid MSR %x, please adapt vmx_possible_passthrough_msrs[]", msr);
+	for (i = 0; i < ARRAY_SIZE(vmx_possible_passthrough_msrs); i++) {
+		if (vmx_possible_passthrough_msrs[i] == msr)
+			return i;
+	}
 
-	return r;
+	WARN(1, "Invalid MSR %x, please adapt vmx_possible_passthrough_msrs[]", msr);
+	return -ENOENT;
 }
 
 struct vmx_uret_msr *vmx_find_uret_msr(struct vcpu_vmx *vmx, u32 msr)
@@ -3954,6 +3945,7 @@ 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 +3955,13 @@ 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);
-		}
+	 */
+	idx = vmx_get_passthrough_msr_slot(msr);
+	if (idx >= 0) {
+		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 +3987,7 @@ 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 +3998,12 @@ 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);
-		}
+	idx = vmx_get_passthrough_msr_slot(msr);
+	if (idx >= 0) {
+		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)

base-commit: 342c6dfc2a0ae893394a6f894acd1d1728c009f2
--