Re: [PATCH v2 00/30] KVM: s390: enable zPCI for interpretive execution

[Pierre Morel]

On 1/14/22 21:31, Matthew Rosato wrote:
> Enable interpretive execution of zPCI instructions + adapter interruption
> forwarding for s390x KVM vfio-pci.  This is done by introducing a series
> of new vfio-pci feature ioctls that are unique vfio-pci-zdev (s390x) and
> are used to negotiate the various aspects of zPCI interpretation setup.
> By allowing intepretation of zPCI instructions and firmware delivery of
> interrupts to guests, we can significantly reduce the frequency of guest
> SIE exits for zPCI.  We then see additional gains by handling a hot-path
> instruction that can still intercept to the hypervisor (RPCIT) directly
> in kvm.
>
>  From the perspective of guest configuration, you passthrough zPCI devices
> in the same manner as before, with intepretation support being used by
> default if available in kernel+qemu.
>
> Will reply with a link to the associated QEMU series.

I did the comment in a patch but I think that centralizing it here is 
clearer: I think having a documentation in Documentation/S390 like we 
have already for VFIO AP and VFIO CCW would be a good thing.

--
Pierre Morel
IBM Lab Boeblingen