Messages in this thread | | | Subject | Re: [PATCH 01/10] vfio: ccw: Moving state change out of IRQ context | From | Pierre Morel <> | Date | Tue, 24 Apr 2018 15:07:30 +0200 |
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On 24/04/2018 13:55, Cornelia Huck wrote: > On Tue, 24 Apr 2018 13:49:14 +0200 > Pierre Morel <pmorel@linux.vnet.ibm.com> wrote: > >> On 24/04/2018 11:59, 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) >> We agree. >> >>> 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. >> Yes, agreed too. >> >>> (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.) >> This patch does not change the current functionalities, only >> consolidates the FSM. >> The current way to handle unsolicited interrupts is to report them to >> the guest >> along with the deferred code AFAIU. > My question was more along the line of "do we actually want to > _generate_ a deferred cc1 or unsolicited interrupt, based upon what we > do in our state machine". My guess is no, regardless of the changes you > do in this series. > >>> 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. >> I agree too, it would just make things unnecessary complicated. > I'm a big fan of just throwing everything at the hardware and let it > sort out any races etc. We just need to be sure we don't mix up > interrupts :) > OK, I understand, I can do somthing in the interrupt handler to make sure we do not loose interrupt IRQs.
I make a proposition in V2.
Thanks,
Pierre
-- Pierre Morel Linux/KVM/QEMU in Böblingen - Germany
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