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Wed, 30 Sep 2026 16:03:21 -0400 (EDT) Date: Wed, 30 Sep 2026 14:03:19 -0600 From: Alex Williamson To: Omar Elghoul Cc: linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, hca@linux.ibm.com, gor@linux.ibm.com, agordeev@linux.ibm.com, borntraeger@linux.ibm.com, svens@linux.ibm.com, schnelle@linux.ibm.com, mjrosato@linux.ibm.com, alifm@linux.ibm.com, farman@linux.ibm.com, gbayer@linux.ibm.com, pasic@linux.ibm.com, frankja@linux.ibm.com, imbrenda@linux.ibm.com, alex@shazbot.org Subject: Re: [PATCH v7 4/4] vfio-pci/zdev: Add VFIO FMB device features Message-ID: <20260930140319.66a27f1c@shazbot.org> In-Reply-To: <53c94059-fe7f-48e9-9588-ee07a40d45de@linux.ibm.com> References: <20260922195141.94548-1-oelghoul@linux.ibm.com> <20260922195141.94548-5-oelghoul@linux.ibm.com> <20260930125750.7a5bc3a8@shazbot.org> <53c94059-fe7f-48e9-9588-ee07a40d45de@linux.ibm.com> X-Mailer: Claws Mail 4.4.0 (GTK 3.24.52; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Wed, 30 Sep 2026 15:40:40 -0400 Omar Elghoul wrote: > On 9/30/26 2:57 PM, Alex Williamson wrote: > > On Tue, 22 Sep 2026 15:51:41 -0400 > > Omar Elghoul wrote: > >> diff --git a/drivers/vfio/pci/vfio_pci_zdev.c b/drivers/vfio/pci/vfio_pci_zdev.c > >> index f47f36314a1c..b028de8e08a4 100644 > >> --- a/drivers/vfio/pci/vfio_pci_zdev.c > >> +++ b/drivers/vfio/pci/vfio_pci_zdev.c > >> @@ -219,3 +219,63 @@ void vfio_pci_zdev_close_device(struct vfio_pci_core_device *vdev) > >> if (zpci_kvm_hook.kvm_unregister) > >> zpci_kvm_hook.kvm_unregister(zdev); > >> } > >> + > >> +int vfio_pci_zdev_feature_fmb_enable(struct vfio_pci_core_device *vdev, u32 flags, > >> + void __user *arg, size_t argsz) > >> +{ > >> + struct zpci_dev *zdev; > >> + struct vfio_device_feature_zpci_fmb_enable fmb_enable; > >> + int ret; > >> + > >> + ret = vfio_check_feature(flags, argsz, VFIO_DEVICE_FEATURE_SET, sizeof(fmb_enable)); > >> + if (ret != 1) > >> + return ret; > >> + > >> + zdev = to_zpci(vdev->pdev); > >> + if (!zdev) > >> + return -ENODEV; > >> + > >> + if (copy_from_user(&fmb_enable, arg, sizeof(fmb_enable))) > >> + return -EFAULT; > >> + > >> + guard(mutex)(&zdev->fmb_lock); > >> + > >> + if (fmb_enable.enabled) > >> + return zpci_fmb_reenable_device(zdev); > >> + return zpci_fmb_disable_device(zdev); > >> +} > >> + > >> +int vfio_pci_zdev_feature_fmb_read(struct vfio_pci_core_device *vdev, u32 flags, > >> + void __user *arg, size_t argsz) > >> +{ > >> + struct zpci_dev *zdev; > >> + struct vfio_device_feature_zpci_fmb_read fmb_read; > >> + struct zpci_fmb fmb_bounce; > >> + int ret; > >> + > >> + ret = vfio_check_feature(flags, argsz, VFIO_DEVICE_FEATURE_GET, sizeof(fmb_read)); > >> + if (ret != 1) > >> + return ret; > >> + > >> + zdev = to_zpci(vdev->pdev); > >> + if (!zdev) > >> + return -ENODEV; > >> + > >> + if (copy_from_user(&fmb_read, arg, sizeof(fmb_read))) > >> + return -EFAULT; > >> + if (!fmb_read.data) > >> + return -EINVAL; > >> + > >> + mutex_lock(&zdev->fmb_lock); > >> + if (!zdev->fmb_enabled) { > >> + mutex_unlock(&zdev->fmb_lock); > >> + return -ENOMSG; > >> + } > >> + > >> + memcpy(&fmb_bounce, zdev->fmb, zdev->fmb_length); > >> + mutex_unlock(&zdev->fmb_lock); > > > > A scoped guard would be preferable for consistency with the enable > > path. > > I thought of that too, but then we'd do copy_to_user() while holding the > mutex for longer than is necessary, which I think was pointed out in an > earlier version. Depends how you use it: scoped_guard(mutex, &zdev->fmb_lock) { if (!zdev->fmb_enabled) return -ENOMSG; memcpy(&fmb_bounce, zdev->fmb, zdev->fmb_length); } if (copy_to_user(u64_to_user_ptr(fmb_read.data), &fmb_bounce, zdev->fmb_length)) return -EFAULT; Thanks, Alex