Re: [PATCH 5/6] KVM: x86: Rename "found" variable in kvm_cpuid() to "exact_entry_exists"

[Jan Kiszka]

On 02.03.20 21:35, Sean Christopherson wrote:
> On Mon, Mar 02, 2020 at 09:20:52PM +0100, Jan Kiszka wrote:
> > On 02.03.20 20:57, Sean Christopherson wrote:
> > > Rename "found" in kvm_cpuid() to "exact_entry_exists" to better convey
> > > that the intent of the tracepoint's "found/not found" output is to trace
> > > whether the output values are for the actual requested leaf or for some
> > > other (likely unrelated) leaf that was found while processing entries to
> > > emulate funky CPU behavior, e.g. the max basic leaf on Intel CPUs when
> > > the requested CPUID leaf is out of range.
> > >
> > > Suggested-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
> > > Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> > > ---
> > >   arch/x86/kvm/cpuid.c | 6 +++---
> > >   1 file changed, 3 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> > > index 869526930cf7..b0a4f3c17932 100644
> > > --- a/arch/x86/kvm/cpuid.c
> > > +++ b/arch/x86/kvm/cpuid.c
> > > @@ -1002,10 +1002,10 @@ void kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx,
> > >   {
> > >   	const u32 function = *eax, index = *ecx;
> > >   	struct kvm_cpuid_entry2 *entry;
> > > -	bool found;
> > > +	bool exact_entry_exists;
> > >   	entry = kvm_find_cpuid_entry(vcpu, function, index);
> > > -	found = entry;
> > > +	exact_entry_exists = !!entry;
> > >   	/*
> > >   	 * Intel CPUID semantics treats any query for an out-of-range
> > >   	 * leaf as if the highest basic leaf (i.e. CPUID.0H:EAX) were
> > > @@ -1047,7 +1047,7 @@ void kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx,
> > >   			}
> > >   		}
> > >   	}
> > > -	trace_kvm_cpuid(function, *eax, *ebx, *ecx, *edx, found);
> > > +	trace_kvm_cpuid(function, *eax, *ebx, *ecx, *edx, exact_entry_exists);
> >
> > Actually, I think we also what to change output in the tracepoint.
>
> Oh, I definitely want to change it, but AIUI it's ABI and shouldn't be
> changed.  Paolo?

This can be discovered via the format string in sysfs and handled by the 
consumer. But I'm not an expert in the tracing ABI.

Jan

--
Siemens AG, Corporate Technology, CT RDA IOT SES-DE
Corporate Competence Center Embedded Linux