[PATCH] kvm: x86: Convert return type of *is_valid_rdpmc_ecx() to bool

[PATCH] kvm: x86: Convert return type of *is_valid_rdpmc_ecx() to bool

[Jim Mattson]

These function names sound like predicates, and they have siblings,
*is_valid_msr(), which _are_ predicates. Moreover, there are comments
that essentially warn that these functions behave unexpectedly.

Flip the polarity of the return values, so that they become
predicates, and convert the boolean result to a success/failure code
at the outer call site.

Signed-off-by: Jim Mattson <jmattson@google.com>
---
 arch/x86/kvm/pmu.c           | 2 +-
 arch/x86/kvm/pmu.h           | 4 ++--
 arch/x86/kvm/svm/pmu.c       | 5 ++---
 arch/x86/kvm/vmx/pmu_intel.c | 7 +++----
 arch/x86/kvm/x86.c           | 4 +++-
 5 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
index 0772bad9165c..09873f6488f7 100644
--- a/arch/x86/kvm/pmu.c
+++ b/arch/x86/kvm/pmu.c
@@ -319,7 +319,7 @@ void kvm_pmu_handle_event(struct kvm_vcpu *vcpu)
 }
 
 /* check if idx is a valid index to access PMU */
-int kvm_pmu_is_valid_rdpmc_ecx(struct kvm_vcpu *vcpu, unsigned int idx)
+bool kvm_pmu_is_valid_rdpmc_ecx(struct kvm_vcpu *vcpu, unsigned int idx)
 {
 	return kvm_x86_ops.pmu_ops->is_valid_rdpmc_ecx(vcpu, idx);
 }
diff --git a/arch/x86/kvm/pmu.h b/arch/x86/kvm/pmu.h
index 0e4f2b1fa9fb..59d6b76203d5 100644
--- a/arch/x86/kvm/pmu.h
+++ b/arch/x86/kvm/pmu.h
@@ -32,7 +32,7 @@ struct kvm_pmu_ops {
 	struct kvm_pmc *(*rdpmc_ecx_to_pmc)(struct kvm_vcpu *vcpu,
 		unsigned int idx, u64 *mask);
 	struct kvm_pmc *(*msr_idx_to_pmc)(struct kvm_vcpu *vcpu, u32 msr);
-	int (*is_valid_rdpmc_ecx)(struct kvm_vcpu *vcpu, unsigned int idx);
+	bool (*is_valid_rdpmc_ecx)(struct kvm_vcpu *vcpu, unsigned int idx);
 	bool (*is_valid_msr)(struct kvm_vcpu *vcpu, u32 msr);
 	int (*get_msr)(struct kvm_vcpu *vcpu, struct msr_data *msr_info);
 	int (*set_msr)(struct kvm_vcpu *vcpu, struct msr_data *msr_info);
@@ -149,7 +149,7 @@ void reprogram_counter(struct kvm_pmu *pmu, int pmc_idx);
 void kvm_pmu_deliver_pmi(struct kvm_vcpu *vcpu);
 void kvm_pmu_handle_event(struct kvm_vcpu *vcpu);
 int kvm_pmu_rdpmc(struct kvm_vcpu *vcpu, unsigned pmc, u64 *data);
-int kvm_pmu_is_valid_rdpmc_ecx(struct kvm_vcpu *vcpu, unsigned int idx);
+bool kvm_pmu_is_valid_rdpmc_ecx(struct kvm_vcpu *vcpu, unsigned int idx);
 bool kvm_pmu_is_valid_msr(struct kvm_vcpu *vcpu, u32 msr);
 int kvm_pmu_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info);
 int kvm_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info);
diff --git a/arch/x86/kvm/svm/pmu.c b/arch/x86/kvm/svm/pmu.c
index fdf587f19c5f..871c426ec389 100644
--- a/arch/x86/kvm/svm/pmu.c
+++ b/arch/x86/kvm/svm/pmu.c
@@ -181,14 +181,13 @@ static struct kvm_pmc *amd_pmc_idx_to_pmc(struct kvm_pmu *pmu, int pmc_idx)
 	return get_gp_pmc_amd(pmu, base + pmc_idx, PMU_TYPE_COUNTER);
 }
 
-/* returns 0 if idx's corresponding MSR exists; otherwise returns 1. */
-static int amd_is_valid_rdpmc_ecx(struct kvm_vcpu *vcpu, unsigned int idx)
+static bool amd_is_valid_rdpmc_ecx(struct kvm_vcpu *vcpu, unsigned int idx)
 {
 	struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
 
 	idx &= ~(3u << 30);
 
-	return (idx >= pmu->nr_arch_gp_counters);
+	return idx < pmu->nr_arch_gp_counters;
 }
 
 /* idx is the ECX register of RDPMC instruction */
diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
index b8e0d21b7c8a..1b7456b2177b 100644
--- a/arch/x86/kvm/vmx/pmu_intel.c
+++ b/arch/x86/kvm/vmx/pmu_intel.c
@@ -118,16 +118,15 @@ static struct kvm_pmc *intel_pmc_idx_to_pmc(struct kvm_pmu *pmu, int pmc_idx)
 	}
 }
 
-/* returns 0 if idx's corresponding MSR exists; otherwise returns 1. */
-static int intel_is_valid_rdpmc_ecx(struct kvm_vcpu *vcpu, unsigned int idx)
+static bool intel_is_valid_rdpmc_ecx(struct kvm_vcpu *vcpu, unsigned int idx)
 {
 	struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
 	bool fixed = idx & (1u << 30);
 
 	idx &= ~(3u << 30);
 
-	return (!fixed && idx >= pmu->nr_arch_gp_counters) ||
-		(fixed && idx >= pmu->nr_arch_fixed_counters);
+	return fixed ? idx < pmu->nr_arch_fixed_counters
+		     : idx < pmu->nr_arch_gp_counters;
 }
 
 static struct kvm_pmc *intel_rdpmc_ecx_to_pmc(struct kvm_vcpu *vcpu,
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c1c4e2b05a63..d7def720227d 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7328,7 +7328,9 @@ static void emulator_set_smbase(struct x86_emulate_ctxt *ctxt, u64 smbase)
 static int emulator_check_pmc(struct x86_emulate_ctxt *ctxt,
 			      u32 pmc)
 {
-	return kvm_pmu_is_valid_rdpmc_ecx(emul_to_vcpu(ctxt), pmc);
+	if (kvm_pmu_is_valid_rdpmc_ecx(emul_to_vcpu(ctxt), pmc))
+		return 0;
+	return -EINVAL;
 }
 
 static int emulator_read_pmc(struct x86_emulate_ctxt *ctxt,
-- 
2.34.0.rc0.344.g81b53c2807-goog

Re: [PATCH] kvm: x86: Convert return type of *is_valid_rdpmc_ecx() to bool

[Sean Christopherson]

KVM: x86:

On Thu, Nov 04, 2021, Jim Mattson wrote:
> These function names sound like predicates, and they have siblings,
> *is_valid_msr(), which _are_ predicates. Moreover, there are comments
> that essentially warn that these functions behave unexpectedly.
> 
> Flip the polarity of the return values, so that they become
> predicates, and convert the boolean result to a success/failure code
> at the outer call site.
> 
> Signed-off-by: Jim Mattson <jmattson@google.com>
> ---

Reviewed-by: Sean Christopherson <seanjc@google.com> 

> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index c1c4e2b05a63..d7def720227d 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -7328,7 +7328,9 @@ static void emulator_set_smbase(struct x86_emulate_ctxt *ctxt, u64 smbase)
>  static int emulator_check_pmc(struct x86_emulate_ctxt *ctxt,
>  			      u32 pmc)
>  {
> -	return kvm_pmu_is_valid_rdpmc_ecx(emul_to_vcpu(ctxt), pmc);
> +	if (kvm_pmu_is_valid_rdpmc_ecx(emul_to_vcpu(ctxt), pmc))
> +		return 0;
> +	return -EINVAL;


Heh, after seeing my off-the-cuff suggestion in a patch, I'd probably prefer the
more usual "return 0 at the end".  Either way is a-ok though, and waaaay better
than kvm_pmu_is_valid_rdpmc_ecx() returning '0' on success :-)

	if (!kvm_pmu_is_valid_rdpmc_ecx(emul_to_vcpu(ctxt), pmc))
		return -EINVAL;

	return 0;

>  }
>  
>  static int emulator_read_pmc(struct x86_emulate_ctxt *ctxt,
> -- 
> 2.34.0.rc0.344.g81b53c2807-goog
>