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([2a01:e0a:59e:9d80:527b:9dff:feef:3874]) by smtp.gmail.com with ESMTPSA id s4-20020a372c04000000b007456c75edbbsm4223342qkh.129.2023.04.05.01.02.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 05 Apr 2023 01:02:18 -0700 (PDT) Message-ID: Date: Wed, 5 Apr 2023 10:02:13 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.5.0 Reply-To: eric.auger@redhat.com Subject: Re: [PATCH v3 05/12] vfio/pci: Allow passing zero-length fd array in VFIO_DEVICE_PCI_HOT_RESET Content-Language: en-US To: Alex Williamson , Yi Liu Cc: jgg@nvidia.com, kevin.tian@intel.com, joro@8bytes.org, robin.murphy@arm.com, cohuck@redhat.com, nicolinc@nvidia.com, kvm@vger.kernel.org, mjrosato@linux.ibm.com, chao.p.peng@linux.intel.com, yi.y.sun@linux.intel.com, peterx@redhat.com, jasowang@redhat.com, shameerali.kolothum.thodi@huawei.com, lulu@redhat.com, suravee.suthikulpanit@amd.com, intel-gvt-dev@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, linux-s390@vger.kernel.org, xudong.hao@intel.com, yan.y.zhao@intel.com, terrence.xu@intel.com, yanting.jiang@intel.com References: <20230401144429.88673-1-yi.l.liu@intel.com> <20230401144429.88673-6-yi.l.liu@intel.com> <20230404141838.6a4efdd4.alex.williamson@redhat.com> From: Eric Auger In-Reply-To: <20230404141838.6a4efdd4.alex.williamson@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-s390@vger.kernel.org On 4/4/23 22:18, Alex Williamson wrote: > On Sat, 1 Apr 2023 07:44:22 -0700 > Yi Liu wrote: > >> as an alternative method for ownership check when iommufd is used. In >> this case all opened devices in the affected dev_set are verified to >> be bound to a same valid iommufd value to allow reset. It's simpler >> and faster as user does not need to pass a set of fds and kernel no >> need to search the device within the given fds. >> >> a device in noiommu mode doesn't have a valid iommufd, so this method >> should not be used in a dev_set which contains multiple devices and one >> of them is in noiommu. The only allowed noiommu scenario is that the >> calling device is noiommu and it's in a singleton dev_set. >> >> Suggested-by: Jason Gunthorpe >> Signed-off-by: Jason Gunthorpe >> Reviewed-by: Jason Gunthorpe >> Tested-by: Yanting Jiang >> Signed-off-by: Yi Liu >> --- >> drivers/vfio/pci/vfio_pci_core.c | 42 +++++++++++++++++++++++++++----- >> include/uapi/linux/vfio.h | 9 ++++++- >> 2 files changed, 44 insertions(+), 7 deletions(-) >> >> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c >> index 3696b8e58445..b68fcba67a4b 100644 >> --- a/drivers/vfio/pci/vfio_pci_core.c >> +++ b/drivers/vfio/pci/vfio_pci_core.c >> @@ -180,7 +180,8 @@ static void vfio_pci_probe_mmaps(struct vfio_pci_core_device *vdev) >> struct vfio_pci_group_info; >> static void vfio_pci_dev_set_try_reset(struct vfio_device_set *dev_set); >> static int vfio_pci_dev_set_hot_reset(struct vfio_device_set *dev_set, >> - struct vfio_pci_group_info *groups); >> + struct vfio_pci_group_info *groups, >> + struct iommufd_ctx *iommufd_ctx); >> >> /* >> * INTx masking requires the ability to disable INTx signaling via PCI_COMMAND >> @@ -1277,7 +1278,7 @@ vfio_pci_ioctl_pci_hot_reset_groups(struct vfio_pci_core_device *vdev, >> return ret; >> >> /* Somewhere between 1 and count is OK */ >> - if (!hdr->count || hdr->count > count) >> + if (hdr->count > count) >> return -EINVAL; >> >> group_fds = kcalloc(hdr->count, sizeof(*group_fds), GFP_KERNEL); >> @@ -1326,7 +1327,7 @@ vfio_pci_ioctl_pci_hot_reset_groups(struct vfio_pci_core_device *vdev, >> info.count = hdr->count; >> info.files = files; >> >> - ret = vfio_pci_dev_set_hot_reset(vdev->vdev.dev_set, &info); >> + ret = vfio_pci_dev_set_hot_reset(vdev->vdev.dev_set, &info, NULL); >> >> hot_reset_release: >> for (file_idx--; file_idx >= 0; file_idx--) >> @@ -1341,6 +1342,7 @@ static int vfio_pci_ioctl_pci_hot_reset(struct vfio_pci_core_device *vdev, >> { >> unsigned long minsz = offsetofend(struct vfio_pci_hot_reset, count); >> struct vfio_pci_hot_reset hdr; >> + struct iommufd_ctx *iommufd; >> bool slot = false; >> >> if (copy_from_user(&hdr, arg, minsz)) >> @@ -1355,7 +1357,12 @@ static int vfio_pci_ioctl_pci_hot_reset(struct vfio_pci_core_device *vdev, >> else if (pci_probe_reset_bus(vdev->pdev->bus)) >> return -ENODEV; >> >> - return vfio_pci_ioctl_pci_hot_reset_groups(vdev, &hdr, slot, arg); >> + if (hdr.count) >> + return vfio_pci_ioctl_pci_hot_reset_groups(vdev, &hdr, slot, arg); >> + >> + iommufd = vfio_iommufd_physical_ictx(&vdev->vdev); >> + >> + return vfio_pci_dev_set_hot_reset(vdev->vdev.dev_set, NULL, iommufd); >> } >> >> static int vfio_pci_ioctl_ioeventfd(struct vfio_pci_core_device *vdev, >> @@ -2327,6 +2334,9 @@ static bool vfio_dev_in_groups(struct vfio_pci_core_device *vdev, >> { >> unsigned int i; >> >> + if (!groups) >> + return false; >> + >> for (i = 0; i < groups->count; i++) >> if (vfio_file_has_dev(groups->files[i], &vdev->vdev)) >> return true; >> @@ -2402,13 +2412,25 @@ static int vfio_pci_dev_set_pm_runtime_get(struct vfio_device_set *dev_set) >> return ret; >> } >> >> +static bool vfio_dev_in_iommufd_ctx(struct vfio_pci_core_device *vdev, >> + struct iommufd_ctx *iommufd_ctx) >> +{ >> + struct iommufd_ctx *iommufd = vfio_iommufd_physical_ictx(&vdev->vdev); >> + >> + if (!iommufd) >> + return false; >> + >> + return iommufd == iommufd_ctx; >> +} >> + >> /* >> * We need to get memory_lock for each device, but devices can share mmap_lock, >> * therefore we need to zap and hold the vma_lock for each device, and only then >> * get each memory_lock. >> */ >> static int vfio_pci_dev_set_hot_reset(struct vfio_device_set *dev_set, >> - struct vfio_pci_group_info *groups) >> + struct vfio_pci_group_info *groups, >> + struct iommufd_ctx *iommufd_ctx) >> { >> struct vfio_pci_core_device *cur_mem; >> struct vfio_pci_core_device *cur_vma; >> @@ -2448,9 +2470,17 @@ static int vfio_pci_dev_set_hot_reset(struct vfio_device_set *dev_set, >> * >> * Otherwise all opened devices in the dev_set must be >> * contained by the set of groups provided by the user. >> + * >> + * If user provides a zero-length array, then all the >> + * opened devices must be bound to a same iommufd_ctx. >> + * >> + * If all above checks are failed, reset is allowed only if >> + * the calling device is in a singleton dev_set. >> */ >> if (cur_vma->vdev.open_count && >> - !vfio_dev_in_groups(cur_vma, groups)) { >> + !vfio_dev_in_groups(cur_vma, groups) && >> + !vfio_dev_in_iommufd_ctx(cur_vma, iommufd_ctx) && >> + (dev_set->device_count > 1)) { > This last condition looks buggy to me, we need all conditions to be > true to generate an error here, which means that for a singleton > dev_set, it doesn't matter what group fds are passed, if any, or whether > the iommufd context matches. I think in fact this means that the empty > array path is equally available for group use cases with a singleton > dev_set, but we don't enable it for multiple device dev_sets like we do > iommufd. > > You pointed out a previous issue with hot-reset info and no-iommu where > if other affected devices are not bound to vfio-pci the info ioctl > returns error. That's handled in the hot-reset ioctl by the fact that > all affected devices must be in the dev_set and therefore bound to > vfio-pci drivers. So it seems to me that aside from the spurious error > because we can't report an iommu group when none exists, and didn't > spot it to invent an invalid group for debugging, hot-reset otherwise > works with no-iommu just like it does for iommu backed devices. We > don't currently require singleton no-iommu dev_sets afaict. > > I'll also note that if the dev_set is singleton, this suggests that > pci_reset_function() can make use of bus reset, so a hot-reset is > accessible via VFIO_DEVICE_RESET if the appropriate reset method is > selected. > > Therefore, I think as written, the singleton dev_set hot-reset is > enabled for iommufd and (unintentionally?) for the group path, while > also negating a requirement for a group fd or that a provided group fd > actually matches the device in this latter case. The null-array > approach is not however extended to groups for more general use. > Additionally, limiting no-iommu hot-reset to singleton dev_sets > provides only a marginal functional difference vs VFIO_DEVICE_RESET. > Thanks, > > Alex What bout introducing a helper static bool is_reset_ok(pdev, groups, ctx) {     if (!pdev->vdev.open_count)         return true;     if (groups && vfio_dev_in_groups(pdev, groups))         return true;     if (ctx && vfio_dev_in_iommufd_ctx(pdev, ctx)         return true;     return false; } Assuming the above logic is correct I think this would make the code more readable Thanks Eric >> ret = -EINVAL; >> goto err_undo; >> } >> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h >> index f96e5689cffc..17aa5d09db41 100644 >> --- a/include/uapi/linux/vfio.h >> +++ b/include/uapi/linux/vfio.h >> @@ -679,7 +679,14 @@ struct vfio_pci_hot_reset_info { >> * the calling user must ensure all affected devices, if opened, are >> * owned by itself. >> * >> - * The ownership is proved by an array of group fds. >> + * The ownership can be proved by: >> + * - An array of group fds >> + * - A zero-length array >> + * >> + * In the last case all affected devices which are opened by this user >> + * must have been bound to a same iommufd. If the calling device is in >> + * noiommu mode (no valid iommufd) then it can be reset only if the reset >> + * doesn't affect other devices. >> * >> * Return: 0 on success, -errno on failure. >> */