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

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Date:   Tue, 22 May 2018 17:41:20 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     Pierre Morel <pmorel@...ux.vnet.ibm.com>
Cc:     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 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?