Re: [PATCH v2] s390x: adapter routes error handling

[Cornelia Huck <cohuck@redhat.com>]

On Fri, 17 Jan 2020 12:22:45 +0100
Christian Borntraeger <borntraeger@de.ibm.com> wrote:

> On 17.01.20 12:11, Cornelia Huck wrote:
> > If the kernel irqchip has been disabled, we don't want the
> > {add,release}_adapter_routes routines to call any kvm_irqchip_*
> > interfaces, as they may rely on an irqchip actually having been
> > created. Just take a quick exit in that case instead.
> > 
> > Also initialize routes->gsi[] with -1 in the virtio-ccw handling,
> > to make sure we don't trip over other errors, either. (Nobody
> > else uses the gsi array in that structure.)
> > 
> > Fixes: d426d9fba8ea ("s390x/virtio-ccw: wire up irq routing and irqfds")
> > Signed-off-by: Cornelia Huck <cohuck@redhat.com>  
> 
> I think it was actually quite good to see an error, because something went wrong
> (kvmirqchip being off). Now the error (crash) was certainly a bad one.
> What happens after this patch?
> To me it _looks_ like every caller of set_guest_notifiers would get the ENOSYS
> and bail out with an error so this should be ok, but it would be good
> to add something to the patch description that says so.
> 
> Something like "instead of crashing we now fail with an error message for vhost
> and friends"
> of course only if this is true.

It should work in the same way as it does for tcg right now (we return
-ENOSYS in the non-kvm flic as well). If you're not using irqfd,
everything will work just fine.

What about the following:

"If you are trying to use irqfd without a kernel irqchip, we will fail
with an error."

?

There probably won't be many people seeing anything like this, as I
guess most people will delegate the irqfd setup to libvirt anyway,
which will not turn off the kernel irqchip.