Re: [PATCH v5 11/13] KVM: s390: implement mediated device open callback

From: Pierre Morel
Date: Mon Jun 11 2018 - 05:23:45 EST

On 08/06/2018 23:59, Tony Krowiak wrote:
On 06/07/2018 01:15 PM, Pierre Morel wrote:


Why maintain a list of kvm_ap_matrix structures if we don't have to; it is stored
with the mediated matrix device which is passed in to all of the vfio_ap driver

Because using the vm_list which is a static in kvm makes you stick inside the kvm code.

I understand your point here, but even if we did maintain a list of kvm_ap_matrix structures,
we still need the kvm code to configure the guest's CRYCB and eventually ECA.28. There is
also code in kvm-ap.c that is called from KVM.

The only code from kvm-ap which is called from KVM is temporary code
waiting for Harald to offer the clean interface to AP instructions.

The idea behind kvm-ap.c is that all code
related to configuration of AP structures in KVM is in this one spot.

This I understand, but the code can be in one spot inside VFIO_AP instead
of inside KVM.
Putting the code inside KVM induce dependencies between KVM and AP
while the kvm/vfio interface allows to avoid this dependency.

The purpose of VFIO_AP is to handle the CRYCB, all get/clear/set crycb masks
functions should be in VFIO AP.

If we use wrappers in KVM, since the CRYCB is an a SIE extension,
it is legitimate, the KVM interface to the CRYCB should only
handle bitmaps and be unaware of the vfio_ap internal structures.

Another concern, the kvm_ap_validate_queue_sharing() should not be
inside KVM because it is a decision of current VFIO_AP driver
to not share the queues between guest of level 2.

The Z architecture does not allow to share AP queues between
guests of level 1 but we could re-engineer the AP bus and the '
VFIO AP to offer queue sharing for guest level 2.

This would be a new VFIO_AP driver (and an AP bus extension).
We should not have to change KVM for this.



Pierre Morel
Linux/KVM/QEMU in BÃblingen - Germany