On Mon, Mar 30, 2020 at 08:29:26PM -0700, Kang, Luwei wrote: > > > > On Wed, Mar 18, 2020 at 11:48:18AM +0800, Luwei Kang wrote: > > Ah, right. What about enhancing intel_pt_handle_vmx() and 'struct pt' to > > replace vmx_on with a field that incorporates the KVM mode? > > Some history is the host perf didn't fully agree with introducing HOST_GUEST > mode for PT in KVM. Because the KVM will disable the host trace before > VM-entry in HOST_GUEST mode and KVM guest will win in this case. e.g. Intel > PT has been enabled in KVM guest and the host wants to start system-wide > trace(collect all the trace on this system) at this time, the trace produced > by the Guest OS will be saved in guest PT buffer and host buffer can't get > this. So I prefer don't introduce the KVM PT mode to host perf framework. The > similar problem happens on PEBS virtualization via DS as well. A maintainer's distaste for a feature isn't a good reason to put a hack into KVM. Perf burying its head in the sand won't change the fact that "pt->vmx_on" is poorly named and misleading. Disagreement over features is fine, but things will go sideways quick if perf and KVM are outright hostile towards each other.
