Re: [RFC 08/20] vfio/pci: Add VFIO_DEVICE_BIND_IOMMUFD

David Gibson
2021-09-29T06:27:54Z

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On Sun, Sep 19, 2021 at 02:38:36PM +0800, Liu Yi L wrote:
> This patch adds VFIO_DEVICE_BIND_IOMMUFD for userspace to bind the vfio
> device to an iommufd. No VFIO_DEVICE_UNBIND_IOMMUFD interface is provided
> because it's implicitly done when the device fd is closed.
>
> In concept a vfio device can be bound to multiple iommufds, each hosting
> a subset of I/O address spaces attached by this device.

I really feel like this many<->many mapping between devices is going
to be super-confusing, and therefore make it really hard to be
confident we have all the rules right for proper isolation.

That's why I was suggesting a concept like endpoints, to break this
into two many<->one relationships. I'm ok if that isn't visible in
the user API, but I think this is going to be really hard to keep
track of if it isn't explicit somewhere in the internals.

> However as a
> starting point (matching current vfio), only one I/O address space is
> supported per vfio device. It implies one device can only be attached
> to one iommufd at this point.
>
> Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
> ---
> drivers/vfio/pci/Kconfig | 1 +
> drivers/vfio/pci/vfio_pci.c | 72 ++++++++++++++++++++++++++++-
> drivers/vfio/pci/vfio_pci_private.h | 8 ++++
> include/uapi/linux/vfio.h | 30 ++++++++++++
> 4 files changed, 110 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/vfio/pci/Kconfig b/drivers/vfio/pci/Kconfig
> index 5e2e1b9a9fd3..3abfb098b4dc 100644
> --- a/drivers/vfio/pci/Kconfig
> +++ b/drivers/vfio/pci/Kconfig
> @@ -5,6 +5,7 @@ config VFIO_PCI
> depends on MMU
> select VFIO_VIRQFD
> select IRQ_BYPASS_MANAGER
> + select IOMMUFD
> help
> Support for the PCI VFIO bus driver. This is required to make
> use of PCI drivers using the VFIO framework.
> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> index 145addde983b..20006bb66430 100644
> --- a/drivers/vfio/pci/vfio_pci.c
> +++ b/drivers/vfio/pci/vfio_pci.c
> @@ -552,6 +552,16 @@ static void vfio_pci_release(struct vfio_device *core_vdev)
> vdev->req_trigger = NULL;
> }
> mutex_unlock(&vdev->igate);
> +
> + mutex_lock(&vdev->videv_lock);
> + if (vdev->videv) {
> + struct vfio_iommufd_device *videv = vdev->videv;
> +
> + vdev->videv = NULL;
> + iommufd_unbind_device(videv->idev);
> + kfree(videv);
> + }
> + mutex_unlock(&vdev->videv_lock);
> }
>
> mutex_unlock(&vdev->reflck->lock);
> @@ -780,7 +790,66 @@ static long vfio_pci_ioctl(struct vfio_device *core_vdev,
> container_of(core_vdev, struct vfio_pci_device, vdev);
> unsigned long minsz;
>
> - if (cmd == VFIO_DEVICE_GET_INFO) {
> + if (cmd == VFIO_DEVICE_BIND_IOMMUFD) {
> + struct vfio_device_iommu_bind_data bind_data;
> + unsigned long minsz;
> + struct iommufd_device *idev;
> + struct vfio_iommufd_device *videv;
> +
> + /*
> + * Reject the request if the device is already opened and
> + * attached to a container.
> + */
> + if (vfio_device_in_container(core_vdev))

Usually one would do argument sanity checks before checks that
actually depend on machine state.

> + return -ENOTTY;

This doesn't seem like the right error code. It's a perfectly valid
operation for this device - just not available right now.

> +
> + minsz = offsetofend(struct vfio_device_iommu_bind_data, dev_cookie);
> +
> + if (copy_from_user(&bind_data, (void __user *)arg, minsz))
> + return -EFAULT;
> +
> + if (bind_data.argsz < minsz ||
> + bind_data.flags || bind_data.iommu_fd < 0)
> + return -EINVAL;
> +
> + mutex_lock(&vdev->videv_lock);
> + /*
> + * Allow only one iommufd per device until multiple
> + * address spaces (e.g. vSVA) support is introduced
> + * in the future.
> + */
> + if (vdev->videv) {
> + mutex_unlock(&vdev->videv_lock);
> + return -EBUSY;
> + }
> +
> + idev = iommufd_bind_device(bind_data.iommu_fd,
> + &vdev->pdev->dev,
> + bind_data.dev_cookie);
> + if (IS_ERR(idev)) {
> + mutex_unlock(&vdev->videv_lock);
> + return PTR_ERR(idev);
> + }
> +
> + videv = kzalloc(sizeof(*videv), GFP_KERNEL);
> + if (!videv) {
> + iommufd_unbind_device(idev);
> + mutex_unlock(&vdev->videv_lock);
> + return -ENOMEM;
> + }
> + videv->idev = idev;
> + videv->iommu_fd = bind_data.iommu_fd;
> + /*
> + * A security context has been established. Unblock
> + * user access.
> + */
> + if (atomic_read(&vdev->block_access))
> + atomic_set(&vdev->block_access, 0);
> + vdev->videv = videv;
> + mutex_unlock(&vdev->videv_lock);
> +
> + return 0;
> + } else if (cmd == VFIO_DEVICE_GET_INFO) {
> struct vfio_device_info info;
> struct vfio_info_cap caps = { .buf = NULL, .size = 0 };
> unsigned long capsz;
> @@ -2031,6 +2100,7 @@ static int vfio_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
> mutex_init(&vdev->vma_lock);
> INIT_LIST_HEAD(&vdev->vma_list);
> init_rwsem(&vdev->memory_lock);
> + mutex_init(&vdev->videv_lock);
>
> ret = vfio_pci_reflck_attach(vdev);
> if (ret)
> diff --git a/drivers/vfio/pci/vfio_pci_private.h b/drivers/vfio/pci/vfio_pci_private.h
> index f12012e30b53..bd784accac35 100644
> --- a/drivers/vfio/pci/vfio_pci_private.h
> +++ b/drivers/vfio/pci/vfio_pci_private.h
> @@ -14,6 +14,7 @@
> #include <linux/types.h>
> #include <linux/uuid.h>
> #include <linux/notifier.h>
> +#include <linux/iommufd.h>
>
> #ifndef VFIO_PCI_PRIVATE_H
> #define VFIO_PCI_PRIVATE_H
> @@ -99,6 +100,11 @@ struct vfio_pci_mmap_vma {
> struct list_head vma_next;
> };
>
> +struct vfio_iommufd_device {
> + struct iommufd_device *idev;

Could this be embedded to avoid multiple layers of pointers?

> + int iommu_fd;
> +};
> +
> struct vfio_pci_device {
> struct vfio_device vdev;
> struct pci_dev *pdev;
> @@ -144,6 +150,8 @@ struct vfio_pci_device {
> struct list_head vma_list;
> struct rw_semaphore memory_lock;
> atomic_t block_access;
> + struct mutex videv_lock;
> + struct vfio_iommufd_device *videv;
> };
>
> #define is_intx(vdev) (vdev->irq_type == VFIO_PCI_INTX_IRQ_INDEX)
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index ef33ea002b0b..c902abd60339 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -190,6 +190,36 @@ struct vfio_group_status {
>
> /* --------------- IOCTLs for DEVICE file descriptors --------------- */
>
> +/*
> + * VFIO_DEVICE_BIND_IOMMUFD - _IOR(VFIO_TYPE, VFIO_BASE + 19,
> + * struct vfio_device_iommu_bind_data)
> + *
> + * Bind a vfio_device to the specified iommufd
> + *
> + * The user should provide a device cookie when calling this ioctl. The
> + * cookie is later used in iommufd for capability query, iotlb invalidation
> + * and I/O fault handling.
> + *
> + * User is not allowed to access the device before the binding operation
> + * is completed.
> + *
> + * Unbind is automatically conducted when device fd is closed.
> + *
> + * Input parameters:
> + * - iommu_fd;
> + * - dev_cookie;
> + *
> + * Return: 0 on success, -errno on failure.
> + */
> +struct vfio_device_iommu_bind_data {
> + __u32 argsz;
> + __u32 flags;
> + __s32 iommu_fd;
> + __u64 dev_cookie;
> +};
> +
> +#define VFIO_DEVICE_BIND_IOMMUFD _IO(VFIO_TYPE, VFIO_BASE + 19)
> +
> /**
> * VFIO_DEVICE_GET_INFO - _IOR(VFIO_TYPE, VFIO_BASE + 7,
> * struct vfio_device_info)

--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson

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