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Sat, 25 Jul 2026 11:29:59 +0000 (GMT) Received: from [9.61.19.212] (unknown [9.61.19.212]) by smtpav01.wdc07v.mail.ibm.com (Postfix) with ESMTP; Sat, 25 Jul 2026 11:29:59 +0000 (GMT) Message-ID: <28371b29-4ec3-4162-bcd3-033925238771@linux.ibm.com> Date: Sat, 25 Jul 2026 07:29:58 -0400 Precedence: bulk X-Mailing-List: linux-kernel@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: Matthew Rosato , 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: Eric Farman Autocrypt: addr=farman@linux.ibm.com; keydata= xsFNBF7EiEwBEADGG0EtNKnjp+kQfEVqlqxXoBHjnaQptFpMgxNlz2GtqOujY6nzEWnybIXY 63XUTmMS/tWUf2DTbNCNoWwumGM/I2Gj1uGyMnc4Q477BQlL/e2/9MRaut11rwHsi4zmWylc jO0eFTSLFA8yFBj9osT3uZzk5TwWkD8sf+rD916fFVk0G39uYEd5sjEzjeOf9/dwXyZpjJY6 api1pUHEw7weRvOnllJAfIKFz+KoR6d7ezvMF9zOYHF73FGeSVIYoIEUhA5Cdg60rSlTtHb2 cftex3/cEapvY5bK3CKJ33BVVK10Bht9XfVaA/AOcg/3o5ZbhSIwz4xScGsEVf/Yr368YMdr 3VkCZrmN2ppmVRz/RvAmCyItnmzoVDlSREA6Faw6S0x8Oi7lN0cKh2hy9VPcVupraXJZrdAh GtdU+jrJvSbpdsrX8F7K3RwynbiqGrqC0izGla04hhtei/uwthatglukuxep4PknDGbzijg8 Ef7A8t3qEVklUDrsnNPN5HbR9QQdeF0HuWsDTfILbZv1MICfOK3BCDeT5mJWaJCoQ2rbuljM e1hFSt+mr7GV4h6NcBE+uGIqDSzQORtyTo0uBV4et3cSE84JxOfXBMrj0TlL1855JaIoPWEN uhDRB/dHW8+Fumq2du5hLcaXPka+MO26cNVKVLF0/JjwMTZ9bQARAQABzSJFcmljIEZhcm1h biA8ZmFybWFuQGxpbnV4LmlibS5jb20+wsGuBBMBCABYAhsDBwsJCAcDAgEGFQgCCQoLBBYC AwECHgECF4AdGGh0dHBzOi8va2V5c2VydmVyLnVidW50dS5jb20WIQTSxgUEyej1aM/lh7U4 J7IScb+VYgUCYel8TgAKCRA4J7IScb+VYsHAD/9BSQj7HeJf90PttOmVh35Bb4QyHLZ4g+9x waM59JCKGbiURuNRIGnoRarYXHk6vfy19v8v56Dy1IOlKWaRnizp5Mw9zXBBTCs4fgNbOzY/ SggFY2UzcziXDG29X9zznq5LgY1Jf/cwm1O+rn89GKCZWZhLEB2wKzBj7hum7NBdW+lxfVwp 2qONGDerttWDwAHxJ995k9aDJahq9kIKEMEZbrTQ8JI8KZGoox6+HA04EhoNzxvbV0J+/gLJ 2DkvxN5/xmcD3z+s8B5ev3NarOF17AIA9oCdfu8CPAupcNqJW86m19P5q6AyRB2ZLyAIAAhr HCXrnlh/8HJW1yCOVXxprFdpg1SX1fuArjbFAh53vVVDfkZlwHeTeE7+3y1rtDLfy830pqdD ymv94yey2y1+iZBdbaW0fSC/JkjkOCy8oZawkH3geM4MXV4ze4gbBH6BhxW/0gbEYjnLm3FA 53JcXwhHQFPWIYEYYPvATJi0JUiMY1Znkm3QBWDOCXSrG0tHpAclBa9L40zLRwA1h9YOMFEs qvKijUdvcDf4sTdJ+A6YL66grzul5vNt06NlqsI8HUDHE6vghqyWxupCav2+9b1BuLie++er b8OCo5n3TUHsVMjYJEePU1EkcCa84dCm+CXqPthgRv0sbe4UQEd/qUoVMdWj7Q7FL96mBn0G zM7BTQRexIhMARAAp+k1sC4y7Wtwjqtfu9wIihvY/Vot0v/sKg8CRGRIIRGLiCeA9o+2ZlxC jYztT3Leri5Vo5z09OmRMvoFLJjcHMCG5sYeZwOWNAbeuAxGkIMDSB4pLl3t2c+1PQuMBCd7 +mRZFaMEJfT3nhdUKxy2rp1+YucnA67xGXUJCiD5l9UmhPqa7SAYlpMAqDz7cmBo25c/UNm1 Tpwjrh70jq/4guV5gnprawH8nkRjdKH1JvKWvkuaB7FNZ9IuSHlWclcQX4IQMsaxsU2emAbP VYv7l4YNlKfdlJd8tuEodjuMLOBnr7e9H0hVNUWGFN9bkBNRu3zi/jvhyu15Iu4euR/WdVNu 2K2iYxIfiGMnv0F/a6R1bm10lCJrjyf23J8DYIeH4YmHvOOqYFkq3DWOctlXbb3+aABqjYt3 mkiOLXeplqbo/m3rWcGNd8Q/d1aVA0wm5+Nt3RdSuXG2FHOFdVUQKPLpf1NUH/LInBhS/9Ys ajm6tWXKv7hxwWmyz0u/th6gUra3KpARB1ypebWHULLNzKGwVS81XNs76QhXwX04cyiwLqKb WqLqJKThz+rLa09Ap+eO/UzPfFXvWYWfTeFRIQ/tKF332ZzRR8Xrh/fk//YXyRfpoE/7i5uz ve0HZWp5jXg9Yb+S6g0+XUKznnN9B8WLLCcuRIuSa722070v7KsAEQEAAcLBdgQYAQgAIAIb DBYhBNLGBQTJ6PVoz+WHtTgnshJxv5ViBQJh6XwwAAoJEDgnshJxv5Vib28P/1BYT5gvjuEB A80AXo/IqycicXxDJtrfmyw4COP7bi7AuiDcKyA1wRzC51paKwPFB8Unk2GvG4DV6aDmGTJY +GeCYgthQ+znW461S8B6GqDCAQt2VDNNFVU+gTuh7vYQOgt/OjtiiAvMIJBVRbXoNSRokKOF tpTiXf3ZOsAkot5ZmxE0TV94v18sp/bC84YvFyaxpw5bilT7bmpcq8B8/3yb0kmy6gXLcQAp OnomV3sQBmm050amiO3tvxMNv8J71AvNdTG/rojTDKUl2Nw4f+aw4nVw874m2XpEe9JGRw54 5d2dN8k3GpzcTBe9fCQPOFHOGkQ1CgptDkQuQVD3DIeNzQjXf6xehEymIKnLOkukT2smV0zh fj08z7eiv+dsmnBsbhdM6DKU8qIgkTu77TfHUKjjOY/Mj0YHPuH/J4b1AZFxBhGP0BTKiB2W CR6/49XVKvY1jHxgadSSNCD+f7tEqUNBlVl+P0emMJaYpK1+gy88ma4g3nvyOVe/VzDPjGDC 4HX/6RAR4Dbzry6/epWTTji+7ApzePzmJzPcuzD31ICsgT2dJ6ydxyxxXikBFJqx6BPOF+u+ 1BtKcTz1ek3I2sWvBM1V5CKaFw7iNXxS6HgS2scuAT2awKq+BQlt778/GfBWpXonfqixMvit y8m0x6unNti2MZIUMy0m2gcE In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: MEt7EZIlynfU_8V01Mvaf0jsjZ95xcHf X-Proofpoint-Spam-Info: AW1haW4tMjYwNzI1MDEwNiBTYWx0ZWRfX5SSRZD3RzhKr eg7LujlosFchSd3dEAc2zLughDxYNar3WG+bI5Ct3YAuVd+Igp71+GERJ/3IMWEOn1ynEf/SHIn mCw7C5l1HG9L40bq/F9RvO/MBCO4d0o= X-Authority-Analysis: v=2.4 cv=E/z9Y6dl c=1 sm=1 tr=0 ts=6a649e3a cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==: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=XC0bjJr9udf0u12S4PsA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzI1MDEwNiBTYWx0ZWRfXwgTLg7+3xefm vMBHu7g+BuEaUb4uOSmZVp4ZMJr+4jivmCli/dXCI9UbTYfE/+IVl1XQygH3RLnGLAZTXcIwgA/ Zhh+EN+Zl5ZphgoOjq9O8E1RnY91gOYYg717fYrayAV8UMQaR2ObVBu4WkCuGqb31Q9QpN7dp0q Y6SbDc6Dc+jacsz0kSyDKbTge45Vcmkbevn3I2o6ldJJ3VzIBvPJjb25EqJY7XSpelfXvVbM8Cl 4xBy9GLGxEmeiwvsIEupIzsHleB9ceNvHYhq7GjjFNNlwPgzNAKfqqZ0IY+J86vWIpK3SB5Owv5 qPL476UEMdRmHWmMUjL5XFTTqHZ+VPsbxYr5LkBonykiwr6WCeug6eFTmUjAl7eoUer23OwoB2A TEUY06XFKAP+uRIhrHnQ6TCiLC4oreL39idSi88Ln4gX+XaGnvDmQX3k7qhjX7dECAjWxPb9QFc u+dBpMVSkoi2sOzkfHg== X-Proofpoint-GUID: MEt7EZIlynfU_8V01Mvaf0jsjZ95xcHf 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=2026-07-25_03,2026-07-24_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 priorityscore=1501 spamscore=0 clxscore=1015 phishscore=0 lowpriorityscore=0 bulkscore=0 malwarescore=0 impostorscore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607250106 On 7/24/26 4:18 PM, Matthew Rosato wrote: > 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()? Of course; should've added that in the first place. > > 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 I'm going to add them to cp_* functions, which means no fsm_io_helper. It's only interaction is for calling cp_get_orb anyway (and is the only one to do so), so it'll get covered in that path. > > 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; >