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Fri, 24 Jul 2026 20:18:54 +0000 (GMT) Received: from [9.61.177.4] (unknown [9.61.177.4]) by smtpav04.wdc07v.mail.ibm.com (Postfix) with ESMTP; Fri, 24 Jul 2026 20:18:54 +0000 (GMT) Message-ID: Date: Fri, 24 Jul 2026 16:18:53 -0400 Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 7/8] s390/vfio_ccw: implement a channel program mutex To: Eric Farman , linux-s390@vger.kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Halil Pasic , Christian Borntraeger , stable@vger.kernel.org References: <20260723174751.1180334-1-farman@linux.ibm.com> <20260723174751.1180334-8-farman@linux.ibm.com> Content-Language: en-US From: Matthew Rosato In-Reply-To: <20260723174751.1180334-8-farman@linux.ibm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: Hbyz8xnUCJ9aO1rl7f-06_nh6NcFsNtq X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzI0MDE4MSBTYWx0ZWRfX6HbMmXCgFtw2 kgKLHyccAr7IcvTu/dmXApsgC218maPE54vY5WhCwjKwCOiQiXbyNjHTuT2my6YvxjVnZYw0kUU s0S3zMKQOz960Bn+NZOevK8jwckwgcpz8SYOG6DZi85u7rV605g9BDvzqtiDAWuAQbboOgmxd0U 6XvSBddnqlsb2xP/bBSr0UEML09rpOYHE/tlew4Vhlgji0th6r1DmtZHEsI/qalitPARxfxidDt g6sSmdywiNsYFIoRH5rriTfijqNjt4ILtyFy/Dwyiwe6ts6Ny3epTxI2xt148xFHDoHzpyl2M6x c3bdqFQbs+fIzu1CpVE8cyTWMaDEjYTWnVNMiILFPSGebPjnGquBXzFY98uFD2Tzvd1P3MURvLx eLnZAljqtgm6cFHcLhQtfe2CMLJzeebpr2cqS+fe829J+EndvFWmi6l45Q3u64eXrGgxhGb5mU/ UAMCSKymNcYqUGmM5Kg== X-Proofpoint-Spam-Info: AW1haW4tMjYwNzI0MDE4MSBTYWx0ZWRfX8XlVg2nYUJ5m PdczgysnxBwDxFyWnwb69bwCvOK+cTCq4ctUXkB96ji/OWNg373MJRiiwRM7dO0+qcocVyyotO2 j1bqHY3OrCuxkxuk3s0USNsz2Xt4bUY= X-Proofpoint-GUID: Hbyz8xnUCJ9aO1rl7f-06_nh6NcFsNtq X-Authority-Analysis: v=2.4 cv=SM5ykuvH c=1 sm=1 tr=0 ts=6a63c8b1 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=IkcTkHD0fZMA:10 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=RzCfie-kr_QcCd8fBx8p:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=gFTwVeD1yrmUlQk_w58A:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-07-24_04,2026-07-24_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 lowpriorityscore=0 bulkscore=0 suspectscore=0 adultscore=0 spamscore=0 malwarescore=0 priorityscore=1501 phishscore=0 impostorscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607240181 On 7/23/26 1:47 PM, Eric Farman wrote: > The channel_program struct is manipulated without a serialization > mechanism to ensure consistent behavior. Take a broad stroke of > putting the entire structure behind a mutex, and ensure everything > that needs private->cp holds this mutex. > > There are a couple where the cio layer's subchannel->lock performs > this role in this code, which isn't correct (it should only be used > when touching the actual subchannel, like cio_enable_subchannel()), > so adjust the locations where that spinlock is acquired/released > to correctly coexist with this new mutex. > > Fixes: 0a19e61e6d4c ("vfio: ccw: introduce channel program interfaces") > Cc: stable@vger.kernel.org > Signed-off-by: Eric Farman > --- > drivers/s390/cio/vfio_ccw_drv.c | 10 +++++++++- > drivers/s390/cio/vfio_ccw_fsm.c | 22 +++++++++++++++------- > drivers/s390/cio/vfio_ccw_ops.c | 10 +++++++++- > drivers/s390/cio/vfio_ccw_private.h | 3 +++ > 4 files changed, 36 insertions(+), 9 deletions(-) > > diff --git a/drivers/s390/cio/vfio_ccw_drv.c b/drivers/s390/cio/vfio_ccw_drv.c > index 1a095085bc72..1d8c2ed9da50 100644 > --- a/drivers/s390/cio/vfio_ccw_drv.c > +++ b/drivers/s390/cio/vfio_ccw_drv.c > @@ -91,6 +91,8 @@ void vfio_ccw_sch_io_todo(struct work_struct *work) > > is_final = !(scsw_actl(&irb->scsw) & > (SCSW_ACTL_DEVACT | SCSW_ACTL_SCHACT)); > + > + mutex_lock(&private->cp_mutex); > if (scsw_is_solicited(&irb->scsw)) { > cp_update_scsw(&private->cp, &irb->scsw); > if (is_final && private->state == VFIO_CCW_STATE_CP_PENDING) { > @@ -98,6 +100,8 @@ void vfio_ccw_sch_io_todo(struct work_struct *work) > cp_is_finished = true; > } > } > + mutex_unlock(&private->cp_mutex); > + > mutex_lock(&private->io_mutex); > memcpy(private->io_region->irb_area, irb, sizeof(*irb)); > mutex_unlock(&private->io_mutex); > @@ -259,12 +263,16 @@ static int vfio_ccw_sch_event(struct subchannel *sch, int process) > rc = 0; > > if (cio_update_schib(sch)) { > - if (private) > + if (private) { > + spin_unlock_irqrestore(&sch->lock, flags); > vfio_ccw_fsm_event(private, VFIO_CCW_EVENT_NOT_OPER); > + goto out; > + } > } > > out_unlock: > spin_unlock_irqrestore(&sch->lock, flags); > +out: > > return rc; > } > diff --git a/drivers/s390/cio/vfio_ccw_fsm.c b/drivers/s390/cio/vfio_ccw_fsm.c > index 4d7988ea47ef..9fbe97bd23f9 100644 > --- a/drivers/s390/cio/vfio_ccw_fsm.c > +++ b/drivers/s390/cio/vfio_ccw_fsm.c > @@ -25,17 +25,15 @@ static int fsm_io_helper(struct vfio_ccw_private *private) > unsigned long flags; > int ret; > > - spin_lock_irqsave(&sch->lock, flags); > - > orb = cp_get_orb(&private->cp, sch); Can you extend the documentation for cp_get_orb to indicate that cp_mutex must be held on entry? Actually, better yet, can you use lockdep_assert_held()? Would be a good idea to put these also in other functions that have now an implicit expectation that the mutex will be held, here's the list I came up with? cp_get_orb cp_init cp_prefetch cp_free fsm_io_helper cp_iova_pinned cp_update_scsw In some cases (like cp_get_orb) you'd have to do something like: struct vfio_ccw_private *private = container_of(cp, struct vfio_ccw_private, cp); lockdep_assert_held(&private->cp_mutex); Then this lets us also use lockdep to make sure the mutex is OK now and in the future. > - if (!orb) { > - ret = -EIO; > - goto out; > - } > + if (!orb) > + return -EIO; > > VFIO_CCW_TRACE_EVENT(5, "stIO"); > VFIO_CCW_TRACE_EVENT(5, dev_name(&sch->dev)); > > + spin_lock_irqsave(&sch->lock, flags); > + > /* Issue "Start Subchannel" */ > ccode = ssch(sch->schid, orb); > > @@ -71,7 +69,6 @@ static int fsm_io_helper(struct vfio_ccw_private *private) > default: > ret = ccode; > } > -out: > spin_unlock_irqrestore(&sch->lock, flags); > return ret; > } > @@ -171,7 +168,9 @@ static void fsm_notoper(struct vfio_ccw_private *private, > private->state = VFIO_CCW_STATE_NOT_OPER; > > /* This is usually handled during CLOSE event */ > + mutex_lock(&private->cp_mutex); > cp_free(&private->cp); > + mutex_unlock(&private->cp_mutex); > } > > /* > @@ -252,6 +251,8 @@ static void fsm_io_request(struct vfio_ccw_private *private, > private->state = VFIO_CCW_STATE_CP_PROCESSING; > memcpy(scsw, io_region->scsw_area, sizeof(*scsw)); > > + mutex_lock(&private->cp_mutex); > + > if (scsw->cmd.fctl & SCSW_FCTL_START_FUNC) { > orb = (union orb *)io_region->orb_area; > > @@ -300,6 +301,8 @@ static void fsm_io_request(struct vfio_ccw_private *private, > cp_free(&private->cp); > goto err_out; > } > + > + mutex_unlock(&private->cp_mutex); > return; > } else if (scsw->cmd.fctl & SCSW_FCTL_HALT_FUNC) { > VFIO_CCW_MSG_EVENT(2, > @@ -320,6 +323,7 @@ static void fsm_io_request(struct vfio_ccw_private *private, > } > > err_out: > + mutex_unlock(&private->cp_mutex); > private->state = VFIO_CCW_STATE_IDLE; > trace_vfio_ccw_fsm_io_request(scsw->cmd.fctl, schid, > io_region->ret_code, errstr); > @@ -410,7 +414,11 @@ static void fsm_close(struct vfio_ccw_private *private, > > private->state = VFIO_CCW_STATE_STANDBY; > spin_unlock_irq(&sch->lock); > + > + mutex_lock(&private->cp_mutex); > cp_free(&private->cp); > + mutex_unlock(&private->cp_mutex); > + > return; > > err_unlock: > diff --git a/drivers/s390/cio/vfio_ccw_ops.c b/drivers/s390/cio/vfio_ccw_ops.c > index 032a1cdf4df7..04800cfa779b 100644 > --- a/drivers/s390/cio/vfio_ccw_ops.c > +++ b/drivers/s390/cio/vfio_ccw_ops.c > @@ -38,8 +38,13 @@ static void vfio_ccw_dma_unmap(struct vfio_device *vdev, u64 iova, u64 length) > container_of(vdev, struct vfio_ccw_private, vdev); > > /* Drivers MUST unpin pages in response to an invalidation. */ > - if (!cp_iova_pinned(&private->cp, iova, length)) > + mutex_lock(&private->cp_mutex); > + if (!cp_iova_pinned(&private->cp, iova, length)) { > + mutex_unlock(&private->cp_mutex); > return; > + } > + > + mutex_unlock(&private->cp_mutex); > > vfio_ccw_mdev_reset(private); > } > @@ -50,6 +55,7 @@ static int vfio_ccw_mdev_init_dev(struct vfio_device *vdev) > container_of(vdev, struct vfio_ccw_private, vdev); > > mutex_init(&private->io_mutex); > + mutex_init(&private->cp_mutex); > private->state = VFIO_CCW_STATE_STANDBY; > INIT_LIST_HEAD(&private->crw); > INIT_WORK(&private->io_work, vfio_ccw_sch_io_todo); > @@ -90,6 +96,7 @@ static int vfio_ccw_mdev_init_dev(struct vfio_device *vdev) > out_free_cp: > kfree(private->cp.guest_cp); > out_free_private: > + mutex_destroy(&private->cp_mutex); > mutex_destroy(&private->io_mutex); > return -ENOMEM; > } > @@ -141,6 +148,7 @@ static void vfio_ccw_mdev_release_dev(struct vfio_device *vdev) > kmem_cache_free(vfio_ccw_cmd_region, private->cmd_region); > kmem_cache_free(vfio_ccw_io_region, private->io_region); > kfree(private->cp.guest_cp); > + mutex_destroy(&private->cp_mutex); > mutex_destroy(&private->io_mutex); > } > > diff --git a/drivers/s390/cio/vfio_ccw_private.h b/drivers/s390/cio/vfio_ccw_private.h > index 0501d4bbcdbd..ac5aaa78a74b 100644 > --- a/drivers/s390/cio/vfio_ccw_private.h > +++ b/drivers/s390/cio/vfio_ccw_private.h > @@ -94,6 +94,7 @@ struct vfio_ccw_parent { > * @schib_region: MMIO region for SCHIB information > * @crw_region: MMIO region for getting channel report words > * @num_regions: number of additional regions > + * @cp_mutex: protect against concurrent update of CP resources > * @cp: channel program for the current I/O operation > * @irb: irb info received from interrupt > * @scsw: scsw info > @@ -115,7 +116,9 @@ struct vfio_ccw_private { > struct ccw_crw_region *crw_region; > int num_regions; > > + struct mutex cp_mutex; > struct channel_program cp; > + > struct irb irb; > union scsw scsw; > struct list_head crw;