>>> On 25.02.19 at 15:11, <andrew.coop...@citrix.com> wrote: > On 25/02/2019 13:11, Jan Beulich wrote: >> For Intel, afaics, we indeed produce a blank CPUID leaf in >> all cases, so the behavior looks reasonably consistent. I would >> question though whether a blank CPUID leaf / the absence of any >> counters wouldn't call for #UD instead of #GP(0). > > RDPMC hasn't #UD'd in a quarter of a century, but does #GP in userspace > outside of developer profiling scenarios.
I guess I could equally well say that RDPMC hasn't #GP'd for as long for indexes zero and one. >> Otherwise, >> along the lines of AMD, aren't the first two indexes uniformly valid >> for Intel? > > No - its model specific behaviour. The only difference for more modern > systems is that they have agreed on a common behaviour. > > And that is specifically why implementing 0's is a non-starter - it is > not a remotely sensible use of time to build enough infrastructure to > provide correct model-specific behaviour just for a corner case which > operating systems don't encounter in practice. No-one said you need to consider all cases. But returning zeros for the first four (AMD) or two (Intel) counters can hardly be that big of a problem. Anyway - I'm not going to fight this much more, as vPMU clearly isn't my primary area of interest. But I'll listen to further comments from Boris, wrt giving an eventual ack. Jan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
