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[34.145.75.25]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3ae6e7d429fsm10473502a91.2.2026.10.30.20.57.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 30 Oct 2026 20:57:34 -0700 (PDT) Date: Sat, 31 Oct 2026 03:57:31 +0000 From: Samiullah Khawaja To: Baolu Lu Cc: Joerg Roedel , Will Deacon , Jason Gunthorpe , David Woodhouse , Pranjal Shrivastava , Robin Murphy , Kevin Tian , Alex Williamson , Shuah Khan , iommu@lists.linux.dev, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Pratyush Yadav , Pasha Tatashin , David Matlack , Andrew Morton , Vipin Sharma , Ankit Soni , Nicolin Chen , John Starks Subject: Re: [PATCH v6 16/18] iommufd: Add APIs to preserve/unpreserve a vfio cdev Message-ID: References: <20261025021930.674647-1-skhawaja@google.com> <20261025021930.674647-17-skhawaja@google.com> <07a7f12c-3cd8-4c03-9304-af89c32e0b46@linux.intel.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <07a7f12c-3cd8-4c03-9304-af89c32e0b46@linux.intel.com> On Sat, Oct 31, 2026 at 11:31:47AM +0800, Baolu Lu wrote: >On 10/25/2026 10:19 AM, Samiullah Khawaja wrote: >>Add APIs that can be used to preserve and unpreserve a vfio cdev. Use >>the APIs exported by the IOMMU core to preserve/unpreserve device. >> >>The LUO token of the preserved iommufd is fetched and returned back to >>the caller as that can be used during restore to get the restored >>iommufd. >> >>Reviewed-by: Pranjal Shrivastava >>Signed-off-by: Samiullah Khawaja >>--- >> drivers/iommu/iommufd/device.c | 156 ++++++++++++++++++++++++ >> drivers/iommu/iommufd/iommufd_private.h | 6 + >> include/linux/iommufd.h | 29 +++++ >> 3 files changed, 191 insertions(+) >> >>diff --git a/drivers/iommu/iommufd/device.c b/drivers/iommu/iommufd/device.c >>index a664c70a6fe7..c8ea2e288240 100644 >>--- a/drivers/iommu/iommufd/device.c >>+++ b/drivers/iommu/iommufd/device.c >>@@ -2,6 +2,7 @@ >> /* Copyright (c) 2021-2022, NVIDIA CORPORATION & AFFILIATES >> */ >> #include >>+#include >> #include >> #include >> #include >>@@ -686,6 +687,10 @@ int iommufd_hw_pagetable_attach(struct iommufd_hw_pagetable *hwpt, >> int rc; >> mutex_lock(&igroup->lock); >>+ if (iommufd_device_is_preserved(idev)) { >>+ rc = -EBUSY; >>+ goto err_unlock; >>+ } >> attach = xa_cmpxchg(&igroup->pasid_attach, pasid, NULL, >> XA_ZERO_ENTRY, GFP_KERNEL); >>@@ -868,6 +873,10 @@ iommufd_device_do_replace(struct iommufd_device *idev, ioasid_t pasid, >> int rc; >> mutex_lock(&igroup->lock); >>+ if (iommufd_device_is_preserved(idev)) { >>+ rc = -EBUSY; >>+ goto err_unlock; >>+ } >> attach = xa_load(&igroup->pasid_attach, pasid); >> if (!attach) { >>@@ -1747,3 +1756,150 @@ int iommufd_get_hw_info(struct iommufd_ucmd *ucmd) >> iommufd_put_object(ucmd->ictx, &idev->obj); >> return rc; >> } > >Why is there no such check in iommufd_hw_pagetable_detach()? Detach can't fail, so it is blocked in the caller, vfio_df_ioctl_detach_pt() returns -EBUSY for a preserved device. The other detach path is unbind on close of the device file, which can't happen while LUO holds a reference to it. > >>+ >>+#ifdef CONFIG_IOMMU_LIVEUPDATE >>+static bool _iommufd_device_has_pasid_attachments(struct iommufd_device *idev) >>+{ >>+ struct iommufd_group *igroup = idev->igroup; >>+ unsigned long start = IOMMU_NO_PASID; >>+ >>+ if (xa_find_after(&igroup->pasid_attach, &start, UINT_MAX, XA_PRESENT)) >>+ return true; >>+ >>+ return false; >>+} >>+ >>+/** >>+ * iommufd_device_preserve() - Preserve an iommufd device across live update >>+ * @s: Live update session >>+ * @idev: Target iommufd device >>+ * @iommufd_tokenp: Pointer to store outgoing iommufd token >>+ * >>+ * Return: 0 on success, or negative error code. >>+ */ >>+int iommufd_device_preserve(struct liveupdate_session *s, >>+ struct iommufd_device *idev, >>+ u64 *iommufd_tokenp) >>+{ >>+ struct iommufd_hwpt_paging *hwpt_paging; >>+ struct iommufd_hw_pagetable *hwpt; >>+ struct iommufd_attach *attach; >>+ struct iommufd_group *igroup; >>+ int ret; >>+ >>+ if (!idev) >>+ return -EINVAL; >>+ >>+ if (iommufd_device_is_noiommu(idev)) >>+ return -EOPNOTSUPP; >>+ >>+ igroup = idev->igroup; >>+ mutex_lock(&igroup->lock); >>+ if (idev->liveupdate_preserved) { >>+ ret = -EBUSY; >>+ goto out; >>+ } >>+ >>+ if (_iommufd_device_has_pasid_attachments(idev)) { >>+ ret = -EOPNOTSUPP; >>+ goto out; >>+ } >>+ >>+ attach = xa_load(&igroup->pasid_attach, IOMMU_NO_PASID); >>+ if (!attach) { >>+ ret = -ENOENT; >>+ goto out; >>+ } >>+ >>+ if (!xa_load(&attach->device_array, idev->obj.id)) { >>+ ret = -ENOENT; >>+ goto out; >>+ } >>+ >>+ hwpt = attach->hwpt; >>+ if (!hwpt_is_paging(hwpt)) { >>+ ret = -EOPNOTSUPP; >>+ goto out; >>+ } >>+ >>+ hwpt_paging = to_hwpt_paging(hwpt); >>+ ret = liveupdate_get_token_outgoing(s, idev->ictx->file, iommufd_tokenp); >>+ if (ret) >>+ goto out; >>+ >>+ if (!hwpt_paging->liveupdate_preserved) { >>+ ret = -EINVAL; >>+ goto out; >>+ } >>+ >>+ ret = iommu_preserve_device(hwpt_paging->common.domain, >>+ idev->dev, >>+ *iommufd_tokenp); >>+ >>+ if (!ret) { >>+ igroup->num_liveupdate_preserved++; >>+ idev->liveupdate_preserved = true; >>+ } >>+out: >>+ mutex_unlock(&igroup->lock); >>+ return ret; >>+} >>+EXPORT_SYMBOL_NS_GPL(iommufd_device_preserve, "IOMMUFD"); >>+ >>+/** >>+ * iommufd_device_unpreserve() - Unpreserve an iommufd device >>+ * @s: Live update session >>+ * @idev: Target iommufd device >>+ */ >>+void iommufd_device_unpreserve(struct liveupdate_session *s, >>+ struct iommufd_device *idev) >>+{ >>+ struct iommufd_hwpt_paging *hwpt_paging; >>+ struct iommufd_hw_pagetable *hwpt; >>+ struct iommufd_attach *attach; >>+ struct iommufd_group *igroup; >>+ >>+ if (!idev) >>+ return; >>+ >>+ igroup = idev->igroup; >>+ mutex_lock(&igroup->lock); >>+ if (!idev->liveupdate_preserved) >>+ goto out; >>+ >>+ attach = xa_load(&igroup->pasid_attach, IOMMU_NO_PASID); >>+ if (!attach) { >>+ WARN(1, "IOMMU_NO_PASID attachment not found"); >>+ goto out; >>+ } >>+ >>+ hwpt = attach->hwpt; >>+ if (WARN(!hwpt_is_paging(hwpt), "Attached HWPT is not a paging HWPT")) >>+ goto out; >>+ >>+ hwpt_paging = to_hwpt_paging(hwpt); >>+ if (!hwpt_paging->liveupdate_preserved) { >>+ WARN(1, "Attached domain is not preserved"); >>+ goto out; >>+ } >>+ >>+ iommu_unpreserve_device(hwpt_paging->common.domain, idev->dev); >>+ igroup->num_liveupdate_preserved--; >>+ idev->liveupdate_preserved = false; >>+out: >>+ mutex_unlock(&igroup->lock); >>+} >>+EXPORT_SYMBOL_NS_GPL(iommufd_device_unpreserve, "IOMMUFD"); >>+ >>+/** >>+ * iommufd_device_is_preserved() - Check if an iommufd device is preserved >>+ * @idev: Target iommufd device >>+ * >>+ * Return: true if preserved, false otherwise. >>+ */ >>+bool iommufd_device_is_preserved(struct iommufd_device *idev) >>+{ >>+ return idev && idev->igroup && idev->igroup->num_liveupdate_preserved; >>+} > >How is it different from > > return idev && idev->liveupdate_preserved; > >? > >Device preservation requires a singleton group, so these two are >effectively the same. However, the latter seems more straightforward >given the function's name. Or anything I overlooked? Agreed. I kept the group counter for supporting non-singleton groups later down the road, but for now they are the same. I will use idev->liveupdate_preserved and drop num_liveupdate_preserved. > >>+EXPORT_SYMBOL_NS_GPL(iommufd_device_is_preserved, "IOMMUFD"); >>+#endif >>diff --git a/drivers/iommu/iommufd/iommufd_private.h b/drivers/iommu/iommufd/iommufd_private.h >>index 69d902b69b82..4760fffd2512 100644 >>--- a/drivers/iommu/iommufd/iommufd_private.h >>+++ b/drivers/iommu/iommufd/iommufd_private.h >>@@ -507,6 +507,9 @@ struct iommufd_group { >> struct xarray pasid_attach; >> struct iommufd_sw_msi_maps required_sw_msi; >> phys_addr_t sw_msi_start; >>+#ifdef CONFIG_IOMMU_LIVEUPDATE >>+ int num_liveupdate_preserved; >>+#endif >> }; >> /* >>@@ -524,6 +527,9 @@ struct iommufd_device { >> bool enforce_cache_coherency; >> struct iommufd_vdevice *vdev; >> bool destroying; >>+#ifdef CONFIG_IOMMU_LIVEUPDATE >>+ bool liveupdate_preserved; >>+#endif >> }; >> static inline struct iommufd_device * >>diff --git a/include/linux/iommufd.h b/include/linux/iommufd.h >>index 6e7efe83bc5d..80382aceca18 100644 >>--- a/include/linux/iommufd.h >>+++ b/include/linux/iommufd.h >>@@ -9,6 +9,7 @@ >> #include >> #include >> #include >>+#include >> #include >> #include >> #include >>@@ -213,6 +214,15 @@ int iommufd_access_rw(struct iommufd_access *access, unsigned long iova, >> int iommufd_vfio_compat_ioas_get_id(struct iommufd_ctx *ictx, u32 *out_ioas_id); >> int iommufd_vfio_compat_ioas_create(struct iommufd_ctx *ictx); >> int iommufd_vfio_compat_set_no_iommu(struct iommufd_ctx *ictx); >>+ >>+#ifdef CONFIG_IOMMU_LIVEUPDATE >>+int iommufd_device_preserve(struct liveupdate_session *s, >>+ struct iommufd_device *idev, >>+ u64 *iommufd_tokenp); >>+void iommufd_device_unpreserve(struct liveupdate_session *s, >>+ struct iommufd_device *idev); >>+bool iommufd_device_is_preserved(struct iommufd_device *idev); >>+#endif >> #else /* !CONFIG_IOMMUFD */ >> static inline struct iommufd_ctx *iommufd_ctx_from_file(struct file *file) >> { >>@@ -397,4 +407,23 @@ static inline void iommufd_viommu_destroy_mmap(struct iommufd_viommu *viommu, >> { >> _iommufd_destroy_mmap(viommu->ictx, &viommu->obj, offset); >> } >>+ >>+#if !IS_ENABLED(CONFIG_IOMMU_LIVEUPDATE) || !IS_ENABLED(CONFIG_IOMMUFD) >>+static inline int iommufd_device_preserve(struct liveupdate_session *s, >>+ struct iommufd_device *idev, >>+ u64 *iommufd_tokenp) >>+{ >>+ return 0; > >Why does it return success when IOMMU_LIVEUPDATE is disabled? This is intentional. vfio-pci live update works without IOMMU state preservation, so with IOMMU_LIVEUPDATE disabled the device is still preserved without its IOMMU state. Returning an error here would break that. I will add a comment explaining this. > >>+} >>+ >>+static inline void iommufd_device_unpreserve(struct liveupdate_session *s, >>+ struct iommufd_device *idev) >>+{ >>+} >>+ >>+static inline bool iommufd_device_is_preserved(struct iommufd_device *idev) >>+{ >>+ return false; >>+} >>+#endif >> #endif > >Thanks, >baolu Thanks, Sami