Messages in this thread | | | Subject | Re: [PATCH 01/10] vfio: ccw: Moving state change out of IRQ context | From | Halil Pasic <> | Date | Tue, 24 Apr 2018 18:42:38 +0200 |
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On 04/24/2018 11:59 AM, Cornelia Huck wrote: > On Tue, 24 Apr 2018 10:40:56 +0200 > Pierre Morel <pmorel@linux.vnet.ibm.com> wrote: > >> On 24/04/2018 08:54, Dong Jia Shi wrote: >>> * Pierre Morel <pmorel@linux.vnet.ibm.com> [2018-04-19 16:48:04 +0200]: >>> >>> [...] >>> >>>> @@ -94,9 +83,15 @@ static void vfio_ccw_sch_io_todo(struct work_struct *work) >>>> static void vfio_ccw_sch_irq(struct subchannel *sch) >>>> { >>>> struct vfio_ccw_private *private = dev_get_drvdata(&sch->dev); >>>> + struct irb *irb = this_cpu_ptr(&cio_irb); >>>> >>>> inc_irq_stat(IRQIO_CIO); >>>> - vfio_ccw_fsm_event(private, VFIO_CCW_EVENT_INTERRUPT); >>>> + memcpy(&private->irb, irb, sizeof(*irb)); >>>> + >>>> + WARN_ON(work_pending(&private->io_work)); >>> Hmm, why do we need this? >> >> The current design insure that we have not two concurrent SSCH requests. >> How ever I want here to track spurious interrupt. >> If we implement cancel, halt or clear requests, we also may trigger (AFAIU) >> a second interrupts depending on races between instructions, controller >> and device. > > You won't get an interrupt for a successful cancel. If you do a > halt/clear, you will make the subchannel halt/clear pending in addition > to start pending and you'll only get one interrupt (if the I/O has > progressed far enough, you won't be able to issue a hsch). The > interesting case is: > - guest does a ssch, we do a ssch on the device > - the guest does a csch before it got the interrupt for the ssch > - before we do the csch on the device, the subchannel is already status > pending with completion of the ssch > - after we issue the csch, we get a second interrupt (for the csch) > > I think we should present two interrupts to the guest in that case. > Races between issuing ssch/hsch/csch and the subchannel becoming status > pending happen on real hardware as well, we're just more likely to see > them with the vfio layer in between. >
AFAIU this will be the problem of the person implementing the clear and the halt for vfio-ccw. I.e. it's a non-problem right now.
> (I'm currently trying to recall what we're doing with unsolicited > interrupts. These are fun wrt deferred cc 1; I'm not sure if there are > cases where we want to present a deferred cc to the guest.)
What are 'fun wrt deferred cc 1' again? The deferred cc I understand but wrt does not click at all.
> > Also, doing a second ssch before we got final state for the first one > is perfectly valid. Linux just does not do it, so I'm not sure if we > should invest too much time there. > >> >> We do not need it strongly. >> >>> >>>> + queue_work(vfio_ccw_work_q, &private->io_work); >>>> + if (private->completion) >>>> + complete(private->completion); >>>> } >>>> >>>> static int vfio_ccw_sch_probe(struct subchannel *sch) >>> [...] >>> >> >
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