Re: [PATCH v5 7/9] s390x/pci: enable adapter event notification for interpreted devices

[Pierre Morel]

On 4/22/22 14:10, Matthew Rosato wrote:
> On 4/22/22 5:39 AM, Pierre Morel wrote:
> > On 4/4/22 20:17, Matthew Rosato wrote:
> > > Use the associated kvm ioctl operation to enable adapter event 
> > > notification
> > > and forwarding for devices when requested.  This feature will be set up
> > > with or without firmware assist based upon the 'forwarding_assist' 
> > > setting.
> > >
> > > Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
> > > ---
> > >   hw/s390x/s390-pci-bus.c         | 20 ++++++++++++++---
> > >   hw/s390x/s390-pci-inst.c        | 40 +++++++++++++++++++++++++++++++--
> > >   hw/s390x/s390-pci-kvm.c         | 30 +++++++++++++++++++++++++
> > >   include/hw/s390x/s390-pci-bus.h |  1 +
> > >   include/hw/s390x/s390-pci-kvm.h | 14 ++++++++++++
> > >   5 files changed, 100 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/hw/s390x/s390-pci-bus.c b/hw/s390x/s390-pci-bus.c
> > > index 9c02d31250..47918d2ce9 100644
> > > --- a/hw/s390x/s390-pci-bus.c
> > > +++ b/hw/s390x/s390-pci-bus.c
> > > @@ -190,7 +190,10 @@ void s390_pci_sclp_deconfigure(SCCB *sccb)
> > >           rc = SCLP_RC_NO_ACTION_REQUIRED;
> > >           break;
> > >       default:
> > > -        if (pbdev->summary_ind) {
> > > +        if (pbdev->interp && (pbdev->fh & FH_MASK_ENABLE)) {
> > > +            /* Interpreted devices were using interrupt forwarding */
> > > +            s390_pci_kvm_aif_disable(pbdev);
> >
> > Same remark as for the kernel part.
> > The VFIO device is already initialized and the action is on this 
> > device, Shouldn't we use the VFIO device interface instead of the KVM 
> > interface?
>
> I don't necessarily disagree, but in v3 of the kernel series I was told 
> not to use VFIO ioctls to accomplish tasks that are unique to KVM (e.g. 
> AEN interpretation) and to instead use a KVM ioctl.
>
> VFIO_DEVICE_SET_IRQS won't work as-is for reasons described in the 
> kernel series (e.g. we don't see any of the config space notifiers 
> because of instruction interpretation) -- as far as I can figure we 
> could add our own s390 code to QEMU to issue VFIO_DEVICE_SET_IRQS 
> directly for an interpreted device, but I think would also need 
> s390-specific changes to VFIO_DEVICE_SET_IRQS accommodate this (e.g. 
> maybe something like a VFIO_IRQ_SET_DATA_S390AEN where we can then 
> specify the aen information in vfio_irq_set.data -- or something else I 

Hi,

yes this in VFIO_DEVICE_SET_IRQS is what I think should be done.

> haven't though of yet) -- I can try to look at this some more and see if 
> I get a good idea.



I understood that the demand was concerning the IOMMU but I may be wrong.
For my opinion, the handling of AEN is not specific to KVM but specific 
to the device, for example the code should be the same if Z ever decide 
to use XEN or another hypervizor, except for the GISA part but this part 
is already implemented in KVM in a way it can be used from a device like 
in VFIO AP.

@Alex, what do you think?

Regards,
Pierre


--
Pierre Morel
IBM Lab Boeblingen