On 2015-04-21 13:09, Paolo Bonzini wrote: > > > On 20/04/2015 19:25, Jan Kiszka wrote: >> When hardware supports the g_pat VMCB field, we can use it for emulating >> the PAT configuration that the guest configures by writing to the >> corresponding MSR. >> >> Signed-off-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx> > > I'm not sure about this. The problem is that, unlike Intel, AMD has no > way for the host to force its PAT value and ignore the guest's. I'm > worried about potential performance problems in the guest. I think the guest needs to get what it requests - see my remark in http://thread.gmane.org/gmane.comp.emulators.kvm.devel/135271. > > This is not as bad as on ARM, because the guest cannot disable the cache You mean AMD, I guess. > snooping protocol and thus cache coherency is guaranteed (see tables > 7-10 and 15-20 in the AMD docs), but still I think I'd prefer having > some knob (module parameter) to enable/disable gPAT. It's okay to make > it enabled by default. I still don't get the scenario where we want to override the guest settings. Maybe you can help out - would be valuable for the reasoning in code or commit logs as well. Jan -- Siemens AG, Corporate Technology, CT RTC ITP SES-DE Corporate Competence Center Embedded Linux -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
