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<91402b62c9325b5cbe1824604f9ea2208bdc5385.camel@linux.ibm.com> Subject: Re: [PATCH v8 3/4] s390/pci: Fence FMB enable/disable via debugfs for passthrough devices From: Niklas Schnelle 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, mjrosato@linux.ibm.com, alifm@linux.ibm.com, farman@linux.ibm.com, gbayer@linux.ibm.com, pasic@linux.ibm.com, alex@shazbot.org, frankja@linux.ibm.com, imbrenda@linux.ibm.com In-Reply-To: <20261005154557.57801-4-oelghoul@linux.ibm.com> References: <20261005154557.57801-1-oelghoul@linux.ibm.com> <20261005154557.57801-4-oelghoul@linux.ibm.com> Autocrypt: addr=schnelle@linux.ibm.com; prefer-encrypt=mutual; keydata=mQINBGHm3M8BEAC+MIQkfoPIAKdjjk84OSQ8erd2OICj98+GdhMQpIjHXn/RJdCZLa58k /ay5x0xIHkWzx1JJOm4Lki7WEzRbYDexQEJP0xUia0U+4Yg7PJL4Dg/W4Ho28dRBROoJjgJSLSHwc 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ZJ3cWmC86IFOIXS73KD6Q4JLCVZJhhWl X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYxMDA1MDA3MyBTYWx0ZWRfX8PvlQeaP8l9J oLsVhD+SRDOS4uPToOy5xM5922dHdCBvlQrU9SXj7XrRsTR8tTCXlS6vtN42syBpU1mQwGUrJ6n XfbJoj0TPfTDQGIrKbGO18h5h1TeWR53cLtofPub5Gtml8DdMesQgQqt75Vve5xAK4TjTuomuG4 gHaOGsSUDszUoyN3NFjXmhXM196/VROuDdLfGOoM10HRORIeLLUkBfbHtV0NIw/BtXnCOPWZnjO 95tn6kH0bT/BoPbjqlxp6cTfKGQek0UfXHBcZzhvvUL2m9ZHVv8rFP8nKuVqmItTw/hLQWsbTnV /5tl+WzH3PXJ4hLTyUGKv3DtaDb3m6je9Sh3U2vNoODfZIQe3T8sFwKUQ9vr37PD/4MJL/PFlLY cBi4D0wYS7BFsypCdlMDd7BAZl81PH9Ggc0bTV64ZwgktOwVN3z2SSywUtGxDgv434Vs0RNg+Rm 7AFr0LJm9stQRfHqPwA== X-Proofpoint-Spam-Info: AW1haW4tMjYxMDA1MDA3MyBTYWx0ZWRfX9LShBYr3sWEU sJ11Qu66XsZGj1TLsmSPKyaAl4pxwKMYo/5NcGjXhBbbqJZk7SAjxiGoV3qP9QcLy2E0HVdv5s4 W+M2vSHD1FTs7dBIAj0aLrq0Cy55fok= 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=2026-10-05_05,2026-10-05_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 malwarescore=0 spamscore=0 lowpriorityscore=0 priorityscore=1501 phishscore=0 impostorscore=0 adultscore=0 clxscore=1015 bulkscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2609040000 definitions=main-2610050073 On Mon, 2026-10-05 at 11:45 -0400, Omar Elghoul wrote: > Introduce a fence over enabling or disabling FMB via debugfs when the zPC= I > 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 paralle= l > in the architecture. >=20 > For VFIO devices that are not associated with a KVM (i.e., for userspace > drivers other than QEMU), this fence does not take effect. >=20 > Signed-off-by: Omar Elghoul > Reviewed-by: Matthew Rosato > --- > arch/s390/pci/pci_debug.c | 9 +++++++++ > 1 file changed, 9 insertions(+) >=20 > 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; > =20 > + mutex_lock(&zdev->kzdev_lock); > + if (zdev->kzdev) { > + rc =3D -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; > } > =20 Looks good, thank! Reviewed-by: Niklas Schnelle