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

[Sean Christopherson <seanjc@google.com>]

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
>