From mboxrd@z Thu Jan 1 00:00:00 1970 From: Farhan Ali Subject: Re: [PATCH 3/3] vfio-ccw: add handling for asnyc channel instructions Date: Wed, 28 Nov 2018 10:00:59 -0500 Message-ID: <1feb66c0-ce80-2853-1522-e7d787471fd3@linux.ibm.com> References: <20181122165432.4437-1-cohuck@redhat.com> <20181122165432.4437-4-cohuck@redhat.com> <20181128100249.72d4299a.cohuck@redhat.com> <25021742-a7a8-a90c-a2a3-eb8a78bf1fb0@linux.ibm.com> <20181128155201.5be1d582.cohuck@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20181128155201.5be1d582.cohuck@redhat.com> Content-Language: en-US List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+gceq-qemu-devel2=m.gmane.org@nongnu.org Sender: "Qemu-devel" List-Archive: List-Post: To: Cornelia Huck Cc: linux-s390@vger.kernel.org, Eric Farman , Alex Williamson , Pierre Morel , kvm@vger.kernel.org, qemu-devel@nongnu.org, Halil Pasic , qemu-s390x@nongnu.org List-ID: On 11/28/2018 09:52 AM, Cornelia Huck wrote: > On Wed, 28 Nov 2018 09:31:51 -0500 > Farhan Ali wrote: > >> On 11/28/2018 04:02 AM, Cornelia Huck wrote: >>> On Tue, 27 Nov 2018 14:09:49 -0500 >>> Farhan Ali wrote: >>> >>>> On 11/22/2018 11:54 AM, Cornelia Huck wrote: >>>>> Add a region to the vfio-ccw device that can be used to submit >>>>> asynchronous I/O instructions. ssch continues to be handled by the >>>>> existing I/O region; the new region handles hsch and csch. >>>>> >>>>> Interrupt status continues to be reported through the same channels >>>>> as for ssch. >>>>> >>>>> Signed-off-by: Cornelia Huck >>>>> --- >>>>> drivers/s390/cio/Makefile | 3 +- >>>>> drivers/s390/cio/vfio_ccw_async.c | 88 ++++++++++++++++ >>>>> drivers/s390/cio/vfio_ccw_drv.c | 48 ++++++--- >>>>> drivers/s390/cio/vfio_ccw_fsm.c | 158 +++++++++++++++++++++++++++- >>>>> drivers/s390/cio/vfio_ccw_ops.c | 13 ++- >>>>> drivers/s390/cio/vfio_ccw_private.h | 6 ++ >>>>> include/uapi/linux/vfio.h | 4 + >>>>> include/uapi/linux/vfio_ccw.h | 12 +++ >>>>> 8 files changed, 313 insertions(+), 19 deletions(-) >>>>> create mode 100644 drivers/s390/cio/vfio_ccw_async.c >>>>> >>> >>>>> @@ -76,7 +79,8 @@ static void vfio_ccw_sch_io_todo(struct work_struct *work) >>>>> private = container_of(work, struct vfio_ccw_private, io_work); >>>>> irb = &private->irb; >>>>> >>>>> - if (scsw_is_solicited(&irb->scsw)) { >>>>> + if (scsw_is_solicited(&irb->scsw) && >>>>> + (scsw_fctl(&irb->scsw) & SCSW_FCTL_START_FUNC)) { >>>>> cp_update_scsw(&private->cp, &irb->scsw); >>>>> cp_free(&private->cp); >>>>> } >>>> >>>> I am a little confused about this. Why do we need to update the scsw.cpa >>>> if we have the start function function control bit set? Is it an >>>> optimization? >>> >>> No, it's not an optimization. This is the work function that is >>> scheduled if we get an interrupt for the device. Previously, we only >>> got an interrupt if either the device presented us an unsolicited >>> status or if we got an interrupt as a response to the channel program >>> we submitted. Now, we can get an interrupt for halt/clear subchannel as >>> well, and in that case, we don't necessarily have a cp. >>> >>> [Thinking some more about it, we need to verify if the start function >>> actually remains set if we try to terminate a running channel program >>> with halt/clear. A clear might scrub too much. If that's the case, we >>> also need to free the cp if the start function is not set.] >>> >>> >> >> According to PoPs (Chapter 16: I/O interruptions, under function control): >> >> The start-function indication is also cleared at >> the subchannel during the execution of CLEAR SUB- >> CHANNEL. >> >> So maybe we do need to free the cp. > > Hm... so we need to make sure that cp_update_scsw() and cp_free() only > do something when there's actually a valid cp around and call them > unconditionally. Yes, I agree. Maybe add a ->valid flag to struct channel_program? We could do that. So we would set the flag once we have copied the channel program to kernel memory? since that's when we should care about freeing it. > >