Re: Info regarding AMX support and libvirt implications

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On 2/29/24 13:15, Gianluca Cecchi wrote:
I'm trying to use AMX in my virtual machines.
More info on AMX: <>
My system in test is currently SLES 15 SP5.
I'm also verifying in parallel with Suse (especially regarding the backported features in their 5.14 based kernel), but in the meantime I would like to understand implication, if any, of libvirt in the certification loop I have to analyse.
 From what I see we have in upstream:
. support in the KVM kernel module since 5.17
. support of cpu model SapphireRapids, the first offering AMX as an ISA extension, in QEMU since 7.0

Is there any dependance to check on libvirt too?

Yes, support for the SapphireRapids CPU model was added in libvirt 9.4.0

When I run
virsh cpu-models x86_64
Is libvirt sw stack querying qemu directly? Or the kvm kernel module? Or any internal "database" file?

 From man page it is not clear to me what "known" means:

           cpu-models arch

       Print  the  list  of CPU models known by libvirt for the specified architecture.  Whether a specific hypervisor is able to create a domain which uses any of the printed CPU models is a separate question which can be answered by looking at the domain capabilities  XML  returned by domcapabilities command.  Moreover, for some architectures libvirt does not know any CPU models and the usable CPU models are only limited  by the hypervisor. This command will print that all CPU models are accepted for these architectures and the actual list of supported CPU models can be checked in the domain capabilities XML.

In SLES 15 SP5 with:


There are other requests to support SapphireRapids in SLES15 SP5, but it will take some time to backport patches for all these components and release updated packages.

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