On Fri, May 29, 2026 at 16:12:21 +0200, Jiri Denemark via Devel wrote: > From: Jiri Denemark <[email protected]> > > The arch-capabilities MSR is not defined on AMD CPUs, but KVM has always > been emulating them. Unfortunately, this may cause Windows to crash so > QEMU (since 10.1, commit d3a24134e37d57abd3e7445842cda2717f49e96d) > decided to mask the MSR by default with some additional compatibility > code for older machine types. > > This is all mostly transparent except for probing when we run QEMU > without a machine type and expand the "host" CPU model. With QEMU 10.1 > and newer none of the arch-capabilities features will be shown as > enabled, which may cause unexpected issues for users (such as KubeVirt) > that get the list of all supported features from the host-model CPU > definition in domain capabilities to select possible target nodes for > migration. As a result of the change, no AMD host with new QEMU will be > shown as available for incoming migration from older hosts. > > Since the features are supported on the host (it's possible to > explicitly enable them), but they should not be enabled by default in > host-model CPU, we only add the to domain capabilities when > VIR_CONNECT_GET_DOMAIN_CAPABILITIES_SUPPORTED_CPU_FEATURES flag is set. > > Signed-off-by: Jiri Denemark <[email protected]> > --- > > Notes: > Version 2: > - the features from arch-capabilities MSR are added only when the new > VIR_CONNECT_GET_DOMAIN_CAPABILITIES_SUPPORTED_CPU_FEATURES flag is set > (previously they were enabled for *_EXPAND_CPU_FEATURES) > - the functionality is tested so the appropriate tests are affected by > this change
Reviewed-by: Peter Krempa <[email protected]>
