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

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Date:   Wed, 23 May 2018 10:10:29 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     Pierre Morel <pmorel@...ux.ibm.com>
Cc:     Pierre Morel <pmorel@...ux.vnet.ibm.com>,
        Dong Jia Shi <bjsdjshi@...ux.ibm.com>,
        Dong Jia Shi <bjsdjshi@...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, 23 May 2018 09:50:00 +0200
Pierre Morel <pmorel@...ux.ibm.com> wrote:

> On 22/05/2018 17:41, Cornelia Huck wrote:
> > On Fri, 4 May 2018 13:02:36 +0200
> > Pierre Morel <pmorel@...ux.vnet.ibm.com> wrote:
> >  
> >> On 04/05/2018 03:19, Dong Jia Shi wrote:  
> >>> * Pierre Morel <pmorel@...ux.vnet.ibm.com> [2018-05-03 16:26:29 +0200]:
> >>>     
> >>>> On 02/05/2018 09:46, Dong Jia Shi 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?
> >>>>>     
> >>>> :) Isn't it exactly what my patch series handle?  
> >>> As far as I see, that's not true. ;)
> >>>
> >>> After this series applied,
> >>> vfio_ccw_jumptable[VFIO_CCW_STATE_STANDBY][VFIO_CCW_EVENT_INTERRUPT] is
> >>> still fsm_irq().
> >>>     
> >>
> >> What I mean is, this code tries to handle design problems
> >> without changing too much of the original code at first.
> >>
> >> The problem here is not that the fsm_irq function is called on interrupt,
> >> if we have an interrupt it must be signaled to user land.
> >> The problem is that this state is entered at the wrong moment.
> >>
> >> STANDBY should be entered, during the mdev_open when we realize the QEMU
> >> device,
> >> and not during the probe, in which we should stay in NOT_OPER until we
> >> get the QEMU device.
> >>
> >> The probe() and mdev_open() function should be modified, not the state
> >> table.  
> > So, the takeaway is that we should handle starting via the init
> > callbacks and not via the state machine?
> >  
> hum, sorry, I think that my previous answer was not completely right,
> and did not really answer to Dong Jia comment, yes fsm_irq was not
> at its place, thinking again about the comments of both of you
> I think that we can suppress the INIT event.
> 
> I would like to rebase the patch to include the comments you both did.
> 
> 

Yes, a respin is probably best before we get confused even more :)