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AHgh+RpIO5jSI51pGDRseszpRtBcdiS1mJJ/hvXnzAwo61qVQRkAFQEPO0rsbpX/VDvpt+CWP3Z7LgCxCOE=@vger.kernel.org X-Gm-Message-State: AOJu0Yx0cfNP5xzJZ0SpSZRCsA8nogu+kdVfP0tVAdz4uYmku++RiWY6 TJpMhY5K9ddWWfzgUoF1TaVxpG4cs5mFoVV4IGPhmhYY/PwsnLop9yyQKjQnI3nJ7QaA08Pi/cU Zv/qp44ou1g== X-Received: from pfbcr14.prod.google.com ([2002:a05:6a00:f0e:b0:84a:2de2:315f]) (user=vipinsh job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:94f5:b0:82f:2b0:2809 with SMTP id d2e1a72fcca58-84889637281mr13764500b3a.1.1784042116875; Tue, 14 Jul 2026 08:15:16 -0700 (PDT) Date: Tue, 14 Jul 2026 08:14:52 -0700 In-Reply-To: <20260714151505.3466855-1-vipinsh@google.com> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260714151505.3466855-1-vipinsh@google.com> X-Mailer: git-send-email 2.55.0.795.g602f6c329a-goog Message-ID: <20260714151505.3466855-8-vipinsh@google.com> Subject: [PATCH v5 07/20] vfio: Introduce vfio_find_device() helper From: Vipin Sharma To: kexec@lists.infradead.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kvm@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org Cc: ajayachandra@nvidia.com, alex@shazbot.org, amastro@fb.com, ankita@nvidia.com, apopple@nvidia.com, bhelgaas@google.com, chrisl@kernel.org, christian.koenig@amd.com, corbet@lwn.net, dmatlack@google.com, graf@amazon.com, jacob.pan@linux.microsoft.com, jgg@nvidia.com, jgg@ziepe.ca, jrhilke@google.com, julianr@linux.ibm.com, kees@kernel.org, kevin.tian@intel.com, leon@kernel.org, leonro@nvidia.com, lukas@wunner.de, mattev@meta.com, michal.winiarski@intel.com, parav@nvidia.com, pasha.tatashin@soleen.com, praan@google.com, pratyush@kernel.org, rananta@google.com, rientjes@google.com, rodrigo.vivi@intel.com, rppt@kernel.org, saeedm@nvidia.com, schnelle@linux.ibm.com, skhan@linuxfoundation.org, skhawaja@google.com, vipinsh@google.com, vivek.kasireddy@intel.com, witu@nvidia.com, yanjun.zhu@linux.dev, yi.l.liu@intel.com Content-Type: text/plain; charset="UTF-8" Introduce vfio_find_device() to discover a registered vfio_device from vfio_device_class matching user-provided criteria. To ensure safe lifecycle handling, vfio_find_device() acquires a registration reference (device->refcount) via vfio_device_try_get_registration() rather than relying solely on device.kref taken in class_find_device(). Holding only kref allows vendor modules to unload while external callers hold device pointers, leading to a kernel panic on release. Callers must release the device via vfio_device_put_registration(). Additionally, move refcount_set() prior to vfio_device_add() in __vfio_register_dev() so device->refcount is initialized before the device is published to class lookups, avoiding registration data races. On vfio_device_add() failure, the error path drops the initial registration reference and waits for completion to drain any reference taken by a concurrent lookup before returning the error to the driver. Signed-off-by: Vipin Sharma --- drivers/vfio/vfio_main.c | 64 +++++++++++++++++++++++++++++++++++++--- include/linux/vfio.h | 2 ++ 2 files changed, 62 insertions(+), 4 deletions(-) diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c index 2437af031169..e91fd83dc58d 100644 --- a/drivers/vfio/vfio_main.c +++ b/drivers/vfio/vfio_main.c @@ -13,6 +13,7 @@ #include #include #include +#include #include #include #include @@ -359,17 +360,20 @@ static int __vfio_register_dev(struct vfio_device *device, goto err_out; } - ret = vfio_device_add(device); - if (ret) - goto err_out; - /* Refcounting can't start until the driver calls register */ refcount_set(&device->refcount, 1); + ret = vfio_device_add(device); + if (ret) + goto err_add; + vfio_device_group_register(device); vfio_device_debugfs_init(device); return 0; +err_add: + vfio_device_put_registration(device); + wait_for_completion(&device->comp); err_out: vfio_device_remove_group(device); return ret; @@ -1797,6 +1801,58 @@ int vfio_dma_rw(struct vfio_device *device, dma_addr_t iova, void *data, } EXPORT_SYMBOL(vfio_dma_rw); +struct vfio_device_match_data { + const void *data; + device_match_t match; +}; + +static int vfio_device_match_fn(struct device *dev, const void *data) +{ + struct vfio_device *vdev = container_of(dev, struct vfio_device, device); + const struct vfio_device_match_data *mdata = data; + + if (mdata->match(dev, mdata->data)) { + if (vfio_device_try_get_registration(vdev)) + return 1; + } + return 0; +} + +/** + * vfio_find_device - Find a registered VFIO device matching search criteria + * @data: Context data passed to the @match function + * @match: Device match callback function + * + * Finds a registered VFIO device in the vfio_device_class matching the search + * criteria specified by @match. + * + * On success, this function acquires a registration reference on the matched + * device via vfio_device_try_get_registration(). This pins the device and + * prevents its vendor driver module from unloading or unbinding while the + * reference is held. + * + * Return: Pointer to the matching vfio_device on success, or NULL if no + * matching device is found. The caller MUST release the acquired registration + * reference using vfio_device_put_registration() when finished with the device. + */ +struct vfio_device *vfio_find_device(const void *data, device_match_t match) +{ + struct vfio_device_match_data mdata = { .data = data, .match = match }; + struct device *device; + + device = class_find_device(&vfio_device_class, NULL, &mdata, vfio_device_match_fn); + if (!device) + return NULL; + + /* + * Drop standard kref reference. Caller holds reference from + * vfio_device_try_get_registration(). + */ + put_device(device); + return container_of(device, struct vfio_device, device); +} +EXPORT_SYMBOL_GPL(vfio_find_device); + /* * Module/class support */ diff --git a/include/linux/vfio.h b/include/linux/vfio.h index cf0d941d0410..42c3a9ae3a85 100644 --- a/include/linux/vfio.h +++ b/include/linux/vfio.h @@ -430,4 +430,6 @@ int vfio_virqfd_enable(void *opaque, int (*handler)(void *, void *), void vfio_virqfd_disable(struct virqfd **pvirqfd); void vfio_virqfd_flush_thread(struct virqfd **pvirqfd); +struct vfio_device *vfio_find_device(const void *data, device_match_t match); + #endif /* VFIO_H */ -- 2.55.0.795.g602f6c329a-goog