Re: [PATCH v2 10/10] vfio/pci: Add VFIO_DEVICE_GET_PCI_HOT_RESET_GROUP_INFO

Alex Williamson
2023-03-27T19:27:18Z

On Mon, 27 Mar 2023 02:34:58 -0700
Yi Liu <yi.l.liu@intel.com> wrote:

> This is a preparation for vfio device cdev as cdev gives userspace the
> capability to open device cdev fd and management stack (e.g. libvirt)
> could pass the device fd to the actual user (e.g. QEMU). As a result,
> the actual user has no idea about the device's bus:devfn information.
> This is a problem when user uses VFIO_DEVICE_GET_PCI_HOT_RESET_INFO to
> know the hot reset affected device scope as this ioctl returns bus:devfn
> info. For the fd passing usage, the acutal user cannot map the bus:devfn
> to the devices it has opened via the fd passed from management stack. So
> a new ioctl is required.
>
> This new ioctl reports the list of iommufd dev_id that is opened by the
> user. If there is affected device that is not bound to vfio driver or
> opened by another user, this command shall fail with -EPERM. For the
> noiommu mode in the vfio device cdev path, this shall fail as no dev_id
> would be generated, hence nothing to report.
>
> This ioctl is useless to the users that open vfio group as such users
> have no idea about the iommufd dev_id and it can use the existing
> VFIO_DEVICE_GET_PCI_HOT_RESET_INFO. The user that uses the traditional
> mode vfio group/container would be failed if invoking this ioctl. But
> the user that uses the iommufd compat mode vfio group/container shall
> succeed. This is harmless as long as user cannot make use of it and
> should use VFIO_DEVICE_GET_PCI_HOT_RESET_INFO.

So VFIO_DEVICE_GET_PCI_HOT_RESET_INFO reports a group and bdf, but
VFIO_DEVICE_GET_PCI_HOT_RESET_*GROUP*_INFO is meant for the non-group,
cdev use case and returns a dev_id rather than a group???

Additionally, VFIO_DEVICE_GET_PCI_HOT_RESET_INFO has a flags arg that
isn't used, why do we need a new ioctl vs defining
VFIO_PCI_HOT_RESET_FLAG_IOMMUFD_DEV_ID. In fact, we could define
vfio_dependent_device as:

struct vfio_pci_dependent_device {
union {
__u32 group_id;
__u32 dev_id;
}
__u16 segment;
__u8 bus;
__u8 devfn;
};

If the user calls with the above flag, dev_id is valid, otherwise
group_id. Perhaps segment:buus:devfn could still be filled in with a
NULL/invalid dev_id if the user doesn't have permissions for the device
so that debugging from userspace isn't so opaque. Thanks,

Alex

> Signed-off-by: Yi Liu <yi.l.liu@intel.com>
> ---
> drivers/vfio/pci/vfio_pci_core.c | 98 ++++++++++++++++++++++++++++++++
> include/uapi/linux/vfio.h | 47 +++++++++++++++
> 2 files changed, 145 insertions(+)
>
> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> index 19f5b075d70a..45edf4e9b98b 100644
> --- a/drivers/vfio/pci/vfio_pci_core.c
> +++ b/drivers/vfio/pci/vfio_pci_core.c
> @@ -1181,6 +1181,102 @@ static int vfio_pci_ioctl_reset(struct vfio_pci_core_device *vdev,
> return ret;
> }
>
> +static struct pci_dev *
> +vfio_pci_dev_set_resettable(struct vfio_device_set *dev_set);
> +
> +static int vfio_pci_ioctl_get_pci_hot_reset_group_info(
> + struct vfio_pci_core_device *vdev,
> + struct vfio_pci_hot_reset_group_info __user *arg)
> +{
> + unsigned long minsz =
> + offsetofend(struct vfio_pci_hot_reset_group_info, count);
> + struct vfio_pci_hot_reset_group_info hdr;
> + struct iommufd_ctx *iommufd, *cur_iommufd;
> + u32 count = 0, index = 0, *devices = NULL;
> + struct vfio_pci_core_device *cur;
> + bool slot = false;
> + int ret = 0;
> +
> + if (copy_from_user(&hdr, arg, minsz))
> + return -EFAULT;
> +
> + if (hdr.argsz < minsz)
> + return -EINVAL;
> +
> + hdr.flags = 0;
> +
> + /* Can we do a slot or bus reset or neither? */
> + if (!pci_probe_reset_slot(vdev->pdev->slot))
> + slot = true;
> + else if (pci_probe_reset_bus(vdev->pdev->bus))
> + return -ENODEV;
> +
> + mutex_lock(&vdev->vdev.dev_set->lock);
> + if (!vfio_pci_dev_set_resettable(vdev->vdev.dev_set)) {
> + ret = -EPERM;
> + goto out_unlock;
> + }
> +
> + iommufd = vfio_iommufd_physical_ictx(&vdev->vdev);
> + if (!iommufd) {
> + ret = -EPERM;
> + goto out_unlock;
> + }
> +
> + /* How many devices are affected? */
> + ret = vfio_pci_for_each_slot_or_bus(vdev->pdev, vfio_pci_count_devs,
> + &count, slot);
> + if (ret)
> + goto out_unlock;
> +
> + WARN_ON(!count); /* Should always be at least one */
> +
> + /*
> + * If there's enough space, fill it now, otherwise return -ENOSPC and
> + * the number of devices affected.
> + */
> + if (hdr.argsz < sizeof(hdr) + (count * sizeof(*devices))) {
> + ret = -ENOSPC;
> + hdr.count = count;
> + goto reset_info_exit;
> + }
> +
> + devices = kcalloc(count, sizeof(*devices), GFP_KERNEL);
> + if (!devices) {
> + ret = -ENOMEM;
> + goto reset_info_exit;
> + }
> +
> + list_for_each_entry(cur, &vdev->vdev.dev_set->device_list, vdev.dev_set_list) {
> + cur_iommufd = vfio_iommufd_physical_ictx(&cur->vdev);
> + if (cur->vdev.open_count) {
> + if (cur_iommufd != iommufd) {
> + ret = -EPERM;
> + break;
> + }
> + ret = vfio_iommufd_physical_devid(&cur->vdev, &devices[index]);
> + if (ret)
> + break;
> + index++;
> + }
> + }
> +
> +reset_info_exit:
> + if (copy_to_user(arg, &hdr, minsz))
> + ret = -EFAULT;
> +
> + if (!ret) {
> + if (copy_to_user(&arg->devices, devices,
> + hdr.count * sizeof(*devices)))
> + ret = -EFAULT;
> + }
> +
> + kfree(devices);
> +out_unlock:
> + mutex_unlock(&vdev->vdev.dev_set->lock);
> + return ret;
> +}
> +
> static int vfio_pci_ioctl_get_pci_hot_reset_info(
> struct vfio_pci_core_device *vdev,
> struct vfio_pci_hot_reset_info __user *arg)
> @@ -1404,6 +1500,8 @@ long vfio_pci_core_ioctl(struct vfio_device *core_vdev, unsigned int cmd,
> return vfio_pci_ioctl_get_irq_info(vdev, uarg);
> case VFIO_DEVICE_GET_PCI_HOT_RESET_INFO:
> return vfio_pci_ioctl_get_pci_hot_reset_info(vdev, uarg);
> + case VFIO_DEVICE_GET_PCI_HOT_RESET_GROUP_INFO:
> + return vfio_pci_ioctl_get_pci_hot_reset_group_info(vdev, uarg);
> case VFIO_DEVICE_GET_REGION_INFO:
> return vfio_pci_ioctl_get_region_info(vdev, uarg);
> case VFIO_DEVICE_IOEVENTFD:
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index 25432ef213ee..61b801dfd40b 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -669,6 +669,53 @@ struct vfio_pci_hot_reset_info {
>
> #define VFIO_DEVICE_GET_PCI_HOT_RESET_INFO _IO(VFIO_TYPE, VFIO_BASE + 12)
>
> +/**
> + * VFIO_DEVICE_GET_PCI_HOT_RESET_GROUP_INFO - _IOWR(VFIO_TYPE, VFIO_BASE + 12,
> + * struct vfio_pci_hot_reset_group_info)
> + *
> + * This is used in the vfio device cdev mode. It returns the list of
> + * affected devices (represented by iommufd dev_id) when hot reset is
> + * issued on the current device with which this ioctl is invoked. It
> + * only includes the devices that are opened by the current user in the
> + * time of this command is invoked. This list may change when user opens
> + * new device or close opened device, hence user should re-invoke it
> + * after open/close devices. This command has no guarantee on the result
> + * of VFIO_DEVICE_PCI_HOT_RESET since the not-opened affected device can
> + * be by other users in the window between the two ioctls. If the affected
> + * devices are opened by multiple users, the VFIO_DEVICE_PCI_HOT_RESET
> + * shall fail, detail can check the description of VFIO_DEVICE_PCI_HOT_RESET.
> + *
> + * For the users that open vfio group/container, this ioctl is useless as
> + * they have no idea about the iommufd dev_id returned by this ioctl. For
> + * the users of the traditional mode vfio group/container, this ioctl will
> + * fail as this mode does not use iommufd hence no dev_id to report back.
> + * For the users of the iommufd compat mode vfio group/container, this ioctl
> + * would succeed as this mode uses iommufd as container fd. But such users
> + * still have no idea about the iommufd dev_id as the dev_id is only stored
> + * in kernel in this mode. For the users of the vfio group/container, the
> + * VFIO_DEVICE_GET_PCI_HOT_RESET_INFO should be used to know the hot reset
> + * affected devices.
> + *
> + * Return: 0 on success, -errno on failure:
> + * -enospc = insufficient buffer;
> + * -enodev = unsupported for device;
> + * -eperm = no permission for device, this error comes:
> + * - when there are affected devices that are opened but
> + * not bound to the same iommufd with the current device
> + * with which this ioctl is invoked,
> + * - there are affected devices that are not bound to vfio
> + * driver yet.
> + * - no valid iommufd is bound (e.g. noiommu mode)
> + */
> +struct vfio_pci_hot_reset_group_info {
> + __u32 argsz;
> + __u32 flags;
> + __u32 count;
> + __u32 devices[];
> +};
> +
> +#define VFIO_DEVICE_GET_PCI_HOT_RESET_GROUP_INFO _IO(VFIO_TYPE, VFIO_BASE + 18)
> +
> /**
> * VFIO_DEVICE_PCI_HOT_RESET - _IOW(VFIO_TYPE, VFIO_BASE + 13,
> * struct vfio_pci_hot_reset)