Re: [PATCH 3/6] KVM: x86: Add dedicated emulator helper for grabbing CPUID.maxphyaddr

[Sean Christopherson]

On Tue, Mar 03, 2020 at 11:14:22AM +0100, Paolo Bonzini wrote:
> On 03/03/20 10:48, Jan Kiszka wrote:
> >>
> >> I don't think this is a particularly useful change.  Yes, it's not
> >> intuitive but is it more than a matter of documentation (and possibly
> >> moving the check_cr_write snippet into a separate function)?
> > 
> > Besides the non obvious return value of the current function, this
> > approach also avoids leaving cpuid traces for querying maxphyaddr, which
> > is also not very intuitive IMHO.
> 
> There are already other cases where we leave CPUID traces.  We can just
> stop tracing if check_limit (which should be renamed to from_guest) is
> true; there are other internal cases which call ctxt->ops->get_cpuid,
> such as vendor_intel, and those should also use check_limit==true and
> check the return value of ctxt->ops->get_cpuid.

No, the vendor checks that use get_cpuid() shouldn't do check_limit=true,
they're looking for an exact match on the vendor.

Not that it matters.  @check_limit only comes into play on a vendor check
if CPUID.0 doesn't exist, and @check_limit only effects the output if
CPUID.0 _does_ exist.  I.e. the output for CPUID.0 is unaffected by
@check_limit.