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Tue, 11 May 2021 20:45:42 +0000 (GMT) Received: from b03ledav002.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 9244F136051; Tue, 11 May 2021 20:45:41 +0000 (GMT) Received: from oc4221205838.ibm.com (unknown [9.211.43.140]) by b03ledav002.gho.boulder.ibm.com (Postfix) with ESMTP; Tue, 11 May 2021 20:45:41 +0000 (GMT) Subject: Re: [PATCH v6 3/3] vfio-ccw: Serialize FSM IDLE state with I/O completion To: Eric Farman , Cornelia Huck , Halil Pasic Cc: Jared Rossi , linux-s390@vger.kernel.org, kvm@vger.kernel.org References: <20210511195631.3995081-1-farman@linux.ibm.com> <20210511195631.3995081-4-farman@linux.ibm.com> From: Matthew Rosato Message-ID: <9e8934bd-a832-984f-18f7-e7e66c4db6cf@linux.ibm.com> Date: Tue, 11 May 2021 16:45:40 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.0 MIME-Version: 1.0 In-Reply-To: <20210511195631.3995081-4-farman@linux.ibm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: uwK0fSqZk9jvMgTM17NHJIZLqA4NARUj X-Proofpoint-ORIG-GUID: 7rH9LXMcJ0Cgu6_sYKLiUTka4_kWOfyy X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.391,18.0.761 definitions=2021-05-11_04:2021-05-11,2021-05-11 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 priorityscore=1501 impostorscore=0 malwarescore=0 suspectscore=0 clxscore=1015 phishscore=0 lowpriorityscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2104190000 definitions=main-2105110139 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 5/11/21 3:56 PM, Eric Farman wrote: > Today, the stacked call to vfio_ccw_sch_io_todo() does three things: > > 1) Update a solicited IRB with CP information, and release the CP > if the interrupt was the end of a START operation. > 2) Copy the IRB data into the io_region, under the protection of > the io_mutex > 3) Reset the vfio-ccw FSM state to IDLE to acknowledge that > vfio-ccw can accept more work. > > The trouble is that step 3 is (A) invoked for both solicited and > unsolicited interrupts, and (B) sitting after the mutex for step 2. > This second piece becomes a problem if it processes an interrupt > for a CLEAR SUBCHANNEL while another thread initiates a START, > thus allowing the CP and FSM states to get out of sync. That is: > > CPU 1 CPU 2 > fsm_do_clear() > fsm_irq() > fsm_io_request() > vfio_ccw_sch_io_todo() > fsm_io_helper() > > Since the FSM state and CP should be kept in sync, let's make a > note when the CP is released, and rely on that as an indication > that the FSM should also be reset at the end of this routine and > open up the device for more work. > > Signed-off-by: Eric Farman Thanks for the detailed commit message and comment block -- this makes sense to me. Acked-by: Matthew Rosato > --- > drivers/s390/cio/vfio_ccw_drv.c | 12 ++++++++++-- > 1 file changed, 10 insertions(+), 2 deletions(-) > > diff --git a/drivers/s390/cio/vfio_ccw_drv.c b/drivers/s390/cio/vfio_ccw_drv.c > index 8c625b530035..9b61e9b131ad 100644 > --- a/drivers/s390/cio/vfio_ccw_drv.c > +++ b/drivers/s390/cio/vfio_ccw_drv.c > @@ -86,6 +86,7 @@ static void vfio_ccw_sch_io_todo(struct work_struct *work) > struct vfio_ccw_private *private; > struct irb *irb; > bool is_final; > + bool cp_is_finished = false; > > private = container_of(work, struct vfio_ccw_private, io_work); > irb = &private->irb; > @@ -94,14 +95,21 @@ static void vfio_ccw_sch_io_todo(struct work_struct *work) > (SCSW_ACTL_DEVACT | SCSW_ACTL_SCHACT)); > if (scsw_is_solicited(&irb->scsw)) { > cp_update_scsw(&private->cp, &irb->scsw); > - if (is_final && private->state == VFIO_CCW_STATE_CP_PENDING) > + if (is_final && private->state == VFIO_CCW_STATE_CP_PENDING) { > cp_free(&private->cp); > + cp_is_finished = true; > + } > } > mutex_lock(&private->io_mutex); > memcpy(private->io_region->irb_area, irb, sizeof(*irb)); > mutex_unlock(&private->io_mutex); > > - if (private->mdev && is_final) > + /* > + * Reset to IDLE only if processing of a channel program > + * has finished. Do not overwrite a possible processing > + * state if the final interrupt was for HSCH or CSCH. > + */ > + if (private->mdev && cp_is_finished) > private->state = VFIO_CCW_STATE_IDLE; > > if (private->io_trigger) >