On 25.11.19 13:39, George Dunlap wrote:
Changeset ca2eee92df44 ("x86, hvm: Expose host core/HT topology to HVM guests") attempted to "fake up" a topology which would induce guest operating systems to not treat vcpus as sibling hyperthreads. This involved actually reporting hyperthreading as available, but giving vcpus every other ApicId; which in turn led to doubling the ApicIds per core by bumping the ApicIdCoreSize by one. In particular, Ryzen 3xxx series processors, and reportedly EPYC "Rome" cpus -- have an ApicIdCoreSize of 7; the "fake" topology increases this to 8.Unfortunately, Windows running on modern AMD hardware -- including Ryzen 3xxx series processors, and reportedly EPYC "Rome" cpus -- doesn't seem to cope with this value being higher than 7. (Linux guests have so far continued to cope.) A "proper" fix is complicated and it's too late to fix it either for 4.13, or to backport to supported branches. As a short-term fix, limit this value to 7. This does mean that a Linux guest, booted on such a system without this change, and then migrating to a system with this change, with more than 64 vcpus, would see an apparent topology change. This is a low enough risk in practice that enabling this limit unilaterally, to allow other guests to boot without manual intervention, is worth it. Reported-by: Steven Haigh <net...@crc.id.au> Reported-by: Andreas Kinzler <h...@posteo.de> Signed-off-by: George Dunlap <george.dun...@citrix.com>
Release-acked-by: Juergen Gross <jgr...@suse.com> Juergen _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
