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Thu, 17 Sep 2026 02:23:33 +0000 (GMT) Received: from [9.61.177.109] (unknown [9.61.177.109]) by smtpav04.wdc07v.mail.ibm.com (Postfix) with ESMTP; Thu, 17 Sep 2026 02:23:33 +0000 (GMT) Message-ID: Date: Wed, 16 Sep 2026 22:23:33 -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 v6 3/4] s390/pci: Fence FMB enable/disable via debugfs for passthrough devices To: Omar Elghoul , linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: hca@linux.ibm.com, gor@linux.ibm.com, agordeev@linux.ibm.com, borntraeger@linux.ibm.com, svens@linux.ibm.com, schnelle@linux.ibm.com, alifm@linux.ibm.com, farman@linux.ibm.com, gbayer@linux.ibm.com, pasic@linux.ibm.com, alex@shazbot.org References: <20260916213222.233-1-oelghoul@linux.ibm.com> <20260916213222.233-4-oelghoul@linux.ibm.com> From: Matthew Rosato Content-Language: en-US In-Reply-To: <20260916213222.233-4-oelghoul@linux.ibm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwOTE3MDAyNSBTYWx0ZWRfX9yox+ai1R+MM /+skpQtq+MZyT5UcrkUIKyKBfJMd5UbULc5DTMJsv0zyTOUUG+UfmKsw/Pi+LOmZyYJDD/1liBX hoow+ame2tfS110E2we0b2OZfclRIBIN30kktImp1Z9yAEm/09n5uxeYV275jqKo9JrUPH1aYhS dYoPVBEQKNscMMaThnUpwdPNtU9XBeQk+1blQjyC3AZmH8TuGs0EAn3APfoTeEIRiY32bdNFKcl LAqf4Z54Cnq9Cl3mpLrnmAovRaOCbxfv3hGY9qNGQ50/nkOTxBX+uSWFdzHii3sKi92EkznUTT6 CmkbcmZLr0KvY9b0wn6PoU6Uhy/x/DBAaTs+Wx1E/3wR20wkLW28ZAD3K9++IdNclnMcPQooVfa cB7PzIQDYsNmWZgUUriKwnxg9rpcOzusQEcpEJxm6Prx3KBTWIL2jQfJ1u1LzoZ0XIWD+eDASi9 r3t1D507hsXt6gqLfBg== X-Proofpoint-Spam-Info: AW1haW4tMjYwOTE3MDAyNSBTYWx0ZWRfX0ObCrYXqgcCL +trB20xnDqJWPr/WxR51uuh3pyTYB1IsnKX+PodqV0wkbsoGTMbz+fwbkzeonfv1L92IPVaDdHR U8gzY22jblIrKkaYw44v29eihL+7KqU= X-Authority-Analysis: v=2.4 cv=Zsx4uN7G c=1 sm=1 tr=0 ts=6aab4f28 cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=IkcTkHD0fZMA:10 a=VdqzKS8jKosA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=VnNF1IyMAAAA:8 a=ZFlax1m07u7ZzGQ5DBIA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-ORIG-GUID: AEP-M6-l56XtAxMXekora4CmkBM-o6TU X-Proofpoint-GUID: AEP-M6-l56XtAxMXekora4CmkBM-o6TU X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-09-16_03,2026-09-16_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 impostorscore=0 clxscore=1015 priorityscore=1501 lowpriorityscore=0 bulkscore=0 adultscore=0 phishscore=0 spamscore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2609040000 definitions=main-2609170025 On 9/16/26 5:32 PM, Omar Elghoul wrote: > Introduce a fence over enabling or disabling FMB via debugfs when the zPCI > device is associated with a KVM. This will prevent processes on the host > from tampering with the FMB while the guest is still using it, which may > cause partial counter resets and inconsistent reads which have no parallel > in the architecture. > > For VFIO devices that are not associated with a KVM (i.e., for userspace > drivers other than QEMU), this fence does not take effect. > > Signed-off-by: Omar Elghoul Reviewed-by: Matthew Rosato > --- > arch/s390/pci/pci_debug.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/arch/s390/pci/pci_debug.c b/arch/s390/pci/pci_debug.c > index 44f026ead414..afc52bd5271a 100644 > --- a/arch/s390/pci/pci_debug.c > +++ b/arch/s390/pci/pci_debug.c > @@ -153,6 +153,12 @@ static ssize_t pci_perf_seq_write(struct file *file, const char __user *ubuf, > if (rc) > return rc; > > + mutex_lock(&zdev->kzdev_lock); > + if (zdev->kzdev) { > + rc = -EPERM; > + goto out_unlock_kzdev; > + } > + > mutex_lock(&zdev->fmb_lock); > switch (val) { > case 0: > @@ -163,6 +169,9 @@ static ssize_t pci_perf_seq_write(struct file *file, const char __user *ubuf, > break; > } > mutex_unlock(&zdev->fmb_lock); > + > +out_unlock_kzdev: > + mutex_unlock(&zdev->kzdev_lock); > return rc ? rc : count; > } >