Re: [Qemu-devel] [RFC][patch 3/6] KVM: s390: Add GISA support

[Frank Blaschka <blaschka@linux.vnet.ibm.com>]

On Fri, Sep 05, 2014 at 10:29:26AM +0200, Alexander Graf wrote:
> 
> 
> On 04.09.14 12:52, frank.blaschka@de.ibm.com wrote:
> > From: Frank Blaschka <frank.blaschka@de.ibm.com>
> > 
> > This patch adds GISA (Guest Interrupt State Area) support
> > to s390 kvm. GISA can be used for exitless interrupts. The
> > patch provides a set of functions for GISA related operations
> > like accessing GISA fields or registering ISCs for alert.
> > Exploiters of GISA will follow with additional patches.
> > 
> > Signed-off-by: Frank Blaschka <frank.blaschka@de.ibm.com>
> 
> That's a nice feature. However, please make sure that you maintain the
> abstraction levels.
> 
> What should happen is that you request an irqfd from FLIC. Then you
> associate that irqfd with the PCI device.
> 
> Thanks to that association, both parties can now talk to each other and
> negotiate their GISA number space and make sure things are connected.
> 
> However, it should always be possible to do things without this direct
> IRQ injection.
> 
> So you should be able to receive an irqfd event when an IRQ happened, so
> that VFIO user space applications can also handle interrupts for example.
> 
> And the same applies for interrupt injection. We also need to be able to
> inject an adapter interrupt from QEMU for emulated devices ;).
>

OK, assuming we are doing the vfio solution expoiting GISA would be a
second step. Will take your feedback into account. THX!
> 
> Alex
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