On 07/16/2015 12:39 PM, Andrew Cooper wrote:
On 16/07/15 17:29, Jan Beulich wrote:
On 16.07.15 at 17:50, <boris.ostrov...@oracle.com> wrote:
Can't we set leaf 1's EBX[32:16] to 1?
(I obviously fat-fingered this --- I meant EBX[23:16])
I don't think we should partially overwrite the relevant parts of
CPUID output - either all or nothing (so that things at least
remain consistent).
Possibly more, but specifically for Dario's problem I think this could
resolve that.
Also, there are no masking/override MSRs for that feature leaf on any
hardware I am aware of, and a PV guest using plain `cpuid` will not
observe any attempt of Xen's to control the value.
True, but we already modify other CPUID bits (e.g. we clear
X86_FEATURE_TOPOEXT) so it won't make things much worse. (And again, for
this specific problem CPUID is queried by guest kernel which uses PV
CPUID instruction).
And in general (both for PV and HVM) --- is there any reason to expose
CPU topology at all? I can see it being useful if VCPUs are pinned but
if they are not then it can make performance worse.
-boris
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xen.org
http://lists.xen.org/xen-devel
