On Mon, Apr 30, 2012 at 06:37:12PM +0200, Davidlohr Bueso wrote:
> On Mon, 2012-04-30 at 14:45 +0300, Gleb Natapov wrote:
> > This couid range does not exist on real HW and Intel spec says that
> > "Information returned for highest basic information leaf" will be
> > returned. Not very well defined.
> >
> > Signed-off-by: Gleb Natapov <[email protected]>
> > diff --git a/arch/x86/include/asm/kvm_para.h
> > b/arch/x86/include/asm/kvm_para.h
> > index 99c4bbe..a7a7a94 100644
> > --- a/arch/x86/include/asm/kvm_para.h
> > +++ b/arch/x86/include/asm/kvm_para.h
> > @@ -178,14 +178,16 @@ static inline int kvm_para_available(void)
> > unsigned int eax, ebx, ecx, edx;
> > char signature[13];
> >
> > - cpuid(KVM_CPUID_SIGNATURE, &eax, &ebx, &ecx, &edx);
> > - memcpy(signature + 0, &ebx, 4);
> > - memcpy(signature + 4, &ecx, 4);
> > - memcpy(signature + 8, &edx, 4);
> > - signature[12] = 0;
> > -
> > - if (strcmp(signature, "KVMKVMKVM") == 0)
> > - return 1;
> > + if (cpu_has_hypervisor) {
> > + cpuid(KVM_CPUID_SIGNATURE, &eax, &ebx, &ecx, &edx);
> > + memcpy(signature + 0, &ebx, 4);
> > + memcpy(signature + 4, &ecx, 4);
> > + memcpy(signature + 8, &edx, 4);
> > + signature[12] = 0;
> > +
> > + if (strcmp(signature, "KVMKVMKVM") == 0)
> > + return 1;
> > + }
> >
> > return 0;
> > }
>
> Wouldn't this be better?
>
If I thought it would I would have wrote it like that :) I prefer less exit
points from a function if possible.
> --- a/arch/x86/include/asm/kvm_para.h
> +++ b/arch/x86/include/asm/kvm_para.h
> @@ -170,6 +170,9 @@ static inline int kvm_para_available(void)
> unsigned int eax, ebx, ecx, edx;
> char signature[13];
>
> + if (!cpu_has_hypervisor)
> + return 0;
> +
> cpuid(KVM_CPUID_SIGNATURE, &eax, &ebx, &ecx, &edx);
> memcpy(signature + 0, &ebx, 4);
> memcpy(signature + 4, &ecx, 4);
>
--
Gleb.
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