linux-kernel - Re: [PATCH 04/10] vfio: ccw: replace IO_REQ event with SSCH

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Message-ID: <20180502102217.702870af.cohuck@redhat.com>
Date:   Wed, 2 May 2018 10:22:17 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     Dong Jia Shi <bjsdjshi@...ux.vnet.ibm.com>
Cc:     Pierre Morel <pmorel@...ux.vnet.ibm.com>, pasic@...ux.vnet.ibm.com,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH 04/10] vfio: ccw: replace IO_REQ event with SSCH_REQ
 event

On Wed, 2 May 2018 15:46:22 +0800
Dong Jia Shi <bjsdjshi@...ux.vnet.ibm.com> wrote:

> * Cornelia Huck <cohuck@...hat.com> [2018-04-30 17:33:05 +0200]:
> 
> > On Thu, 26 Apr 2018 15:48:06 +0800
> > Dong Jia Shi <bjsdjshi@...ux.vnet.ibm.com> wrote:
> >   
> > > * Dong Jia Shi <bjsdjshi@...ux.vnet.ibm.com> [2018-04-26 15:30:54 +0800]:
> > > 
> > > [...]
> > >   
> > > > > @@ -179,7 +160,7 @@ static int fsm_irq(struct vfio_ccw_private *private,
> > > > >  	if (private->io_trigger)
> > > > >  		eventfd_signal(private->io_trigger, 1);
> > > > > 
> > > > > -	return private->state;
> > > > > +	return VFIO_CCW_STATE_IDLE;    
> > > > This is not right. For example, if we are in STANDBY state (subch driver
> > > > is probed, but mdev device is not created), we can not jump to IDLE
> > > > state.
> > > >     
> > > I see my problem, for STANDBY state, we should introduce another event
> > > callback for VFIO_CCW_EVENT_INTERRUPT. It doesn't make sense to call
> > > fsm_irq() which tries to signal userspace with interrupt notification
> > > when mdev is not created yet... So we'd need a separated fix for this
> > > issue too.  
> > 
> > But how do we even get into that situation when we don't have an mdev
> > yet?
> >   
> We cann't... So let's assign fsm_nop() as the interrupt callback for
> STANDBY state?

Either that, or have a special fsm_should_not_happen() function that
can pop out a trace message and then continue to do nothing.