On Tue, Sep 28, 2021 at 09:35:05PM +0800, Lu Baolu wrote: > Another issue is, when putting a device into user-dma mode, all devices > belonging to the same iommu group shouldn't be bound with a kernel-dma > driver. Kevin's prototype checks this by READ_ONCE(dev->driver). This is > not lock safe as discussed below, > > https://lore.kernel.org/linux-iommu/20210927130935.GZ964074@xxxxxxxxxx/ > > Any guidance on this? Something like this? int iommu_set_device_dma_owner(struct device *dev, enum device_dma_owner mode, struct file *user_owner) { struct iommu_group *group = group_from_dev(dev); spin_lock(&iommu_group->dma_owner_lock); switch (mode) { case DMA_OWNER_KERNEL: if (iommu_group->dma_users[DMA_OWNER_USERSPACE]) return -EBUSY; break; case DMA_OWNER_SHARED: break; case DMA_OWNER_USERSPACE: if (iommu_group->dma_users[DMA_OWNER_KERNEL]) return -EBUSY; if (iommu_group->dma_owner_file != user_owner) { if (iommu_group->dma_users[DMA_OWNER_USERSPACE]) return -EPERM; get_file(user_owner); iommu_group->dma_owner_file = user_owner; } break; default: spin_unlock(&iommu_group->dma_owner_lock); return -EINVAL; } iommu_group->dma_users[mode]++; spin_unlock(&iommu_group->dma_owner_lock); return 0; } int iommu_release_device_dma_owner(struct device *dev, enum device_dma_owner mode) { struct iommu_group *group = group_from_dev(dev); spin_lock(&iommu_group->dma_owner_lock); if (WARN_ON(!iommu_group->dma_users[mode])) goto err_unlock; if (!iommu_group->dma_users[mode]--) { if (mode == DMA_OWNER_USERSPACE) { fput(iommu_group->dma_owner_file); iommu_group->dma_owner_file = NULL; } } err_unlock: spin_unlock(&iommu_group->dma_owner_lock); } Where, the driver core does before probe: iommu_set_device_dma_owner(dev, DMA_OWNER_KERNEL, NULL) pci_stub/etc does in their probe func: iommu_set_device_dma_owner(dev, DMA_OWNER_SHARED, NULL) And vfio/iommfd does when a struct vfio_device FD is attached: iommu_set_device_dma_owner(dev, DMA_OWNER_USERSPACE, group_file/iommu_file) Jason
