From: Cornelia Huck <cohuck@redhat.com>
To: Pierre Morel <pmorel@linux.vnet.ibm.com>
Cc: Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com>,
pasic@linux.vnet.ibm.com, linux-s390@vger.kernel.org,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Subject: Re: [PATCH 01/10] vfio: ccw: Moving state change out of IRQ context
Date: Tue, 24 Apr 2018 13:55:33 +0200 [thread overview]
Message-ID: <20180424135533.2e9d03dc.cohuck@redhat.com> (raw)
In-Reply-To: <f6253047-e364-c240-c4c5-cf186ca75a7d@linux.vnet.ibm.com>
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 :)
next prev parent reply other threads:[~2018-04-24 11:55 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-19 14:48 [PATCH 00/10] vfio: ccw: Refactoring the VFIO CCW state machine Pierre Morel
2018-04-19 14:48 ` [PATCH 01/10] vfio: ccw: Moving state change out of IRQ context Pierre Morel
[not found] ` <20180424065442.GV12194@bjsdjshi@linux.vnet.ibm.com>
2018-04-24 8:40 ` Pierre Morel
2018-04-24 9:59 ` Cornelia Huck
2018-04-24 11:49 ` Pierre Morel
2018-04-24 11:55 ` Cornelia Huck [this message]
2018-04-24 13:07 ` Pierre Morel
2018-04-24 16:42 ` Halil Pasic
2018-04-25 6:57 ` Cornelia Huck
2018-04-25 11:06 ` Halil Pasic
2018-04-30 13:56 ` Cornelia Huck
2018-04-19 14:48 ` [PATCH 02/10] vfio: ccw: Transform FSM functions to return state Pierre Morel
[not found] ` <20180424072550.GW12194@bjsdjshi@linux.vnet.ibm.com>
2018-04-24 8:22 ` Pierre Morel
2018-04-30 13:58 ` Cornelia Huck
2018-04-19 14:48 ` [PATCH 03/10] vfio: ccw: new SCH_EVENT event Pierre Morel
2018-04-25 8:25 ` Cornelia Huck
2018-04-25 13:54 ` Pierre Morel
[not found] ` <20180426065954.GP5428@bjsdjshi@linux.vnet.ibm.com>
2018-04-30 15:28 ` Cornelia Huck
2018-05-04 8:25 ` Pierre Morel
2018-04-19 14:48 ` [PATCH 04/10] vfio: ccw: replace IO_REQ event with SSCH_REQ event Pierre Morel
2018-04-25 8:41 ` Cornelia Huck
[not found] ` <24f638e4-2f7e-00e1-1efb-ff3fe524bca0@linux.vnet.ibm.com>
2018-04-30 15:30 ` Cornelia Huck
2018-05-03 12:06 ` Pierre Morel
2018-05-22 15:38 ` Cornelia Huck
2018-05-23 8:19 ` Pierre Morel
[not found] ` <20180426073053.GZ12194@bjsdjshi@linux.vnet.ibm.com>
[not found] ` <20180426074806.GB12194@bjsdjshi@linux.vnet.ibm.com>
2018-04-30 15:33 ` Cornelia Huck
[not found] ` <20180502074622.GV5428@bjsdjshi@linux.vnet.ibm.com>
2018-05-02 8:22 ` Cornelia Huck
2018-05-03 14:26 ` Pierre Morel
[not found] ` <20180504011916.GA26081@bjsdjshi@linux.ibm.com>
2018-05-04 11:02 ` Pierre Morel
2018-05-22 15:41 ` Cornelia Huck
2018-05-23 7:50 ` Pierre Morel
2018-05-23 8:10 ` Cornelia Huck
2018-04-19 14:48 ` [PATCH 05/10] vfio: ccw: Suppress unused event parameter Pierre Morel
[not found] ` <20180426073618.GA12194@bjsdjshi@linux.vnet.ibm.com>
2018-05-03 10:34 ` Pierre Morel
2018-04-19 14:48 ` [PATCH 06/10] vfio: ccw: Make FSM functions atomic Pierre Morel
2018-04-19 14:48 ` [PATCH 07/10] vfio: ccw: Introduce the INIT event Pierre Morel
2018-04-30 15:39 ` Cornelia Huck
2018-05-03 10:31 ` Pierre Morel
2018-04-19 14:48 ` [PATCH 08/10] vfio: ccw: Handling reset and shutdown with states Pierre Morel
2018-04-30 15:43 ` Cornelia Huck
2018-04-19 14:48 ` [PATCH 09/10] vfio: ccw: Suppressing the BOXED state Pierre Morel
2018-04-25 8:44 ` Cornelia Huck
2018-04-25 13:55 ` Pierre Morel
2018-04-30 15:47 ` Cornelia Huck
2018-05-03 9:02 ` Pierre Morel
2018-04-19 14:48 ` [PATCH 10/10] vfio: ccw: Let user wait when busy on IO Pierre Morel
2018-04-25 8:48 ` Cornelia Huck
2018-04-25 14:00 ` Pierre Morel
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20180424135533.2e9d03dc.cohuck@redhat.com \
--to=cohuck@redhat.com \
--cc=bjsdjshi@linux.vnet.ibm.com \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-s390@vger.kernel.org \
--cc=pasic@linux.vnet.ibm.com \
--cc=pmorel@linux.vnet.ibm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).