Re: [Intel-gfx] [PATCH v7 9/9] vfio/pci: Allow passing zero-length fd array in VFIO_DEVICE_PCI_HOT_RESET

Liu, Yi L
2023-06-09T00:14:05Z

> From: Alex Williamson <alex.williamson@redhat.com>
> Sent: Friday, June 9, 2023 6:30 AM
>
> On Fri, 2 Jun 2023 05:15:15 -0700
> Yi Liu <yi.l.liu@intel.com> wrote:
>
> > This is the way user to invoke hot-reset for the devices opened by cdev
> > interface. User should check the flag VFIO_PCI_HOT_RESET_FLAG_DEV_ID_OWNED
> > in the output of VFIO_DEVICE_GET_PCI_HOT_RESET_INFO ioctl before doing
> > hot-reset for cdev devices.
> >
> > Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
> > Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> > Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
> > Tested-by: Yanting Jiang <yanting.jiang@intel.com>
> > Signed-off-by: Yi Liu <yi.l.liu@intel.com>
> > ---
> > drivers/vfio/pci/vfio_pci_core.c | 61 ++++++++++++++++++++++++++------
> > include/uapi/linux/vfio.h | 14 ++++++++
> > 2 files changed, 64 insertions(+), 11 deletions(-)
> >
> > diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> > index a615a223cdef..b0eadafcbcf5 100644
> > --- a/drivers/vfio/pci/vfio_pci_core.c
> > +++ b/drivers/vfio/pci/vfio_pci_core.c
> > @@ -181,7 +181,8 @@ static void vfio_pci_probe_mmaps(struct vfio_pci_core_device
> *vdev)
> > struct vfio_pci_group_info;
> > static void vfio_pci_dev_set_try_reset(struct vfio_device_set *dev_set);
> > static int vfio_pci_dev_set_hot_reset(struct vfio_device_set *dev_set,
> > - struct vfio_pci_group_info *groups);
> > + struct vfio_pci_group_info *groups,
> > + struct iommufd_ctx *iommufd_ctx);
> >
> > /*
> > * INTx masking requires the ability to disable INTx signaling via PCI_COMMAND
> > @@ -1308,8 +1309,7 @@ vfio_pci_ioctl_pci_hot_reset_groups(struct
> vfio_pci_core_device *vdev,
> > if (ret)
> > return ret;
> >
> > - /* Somewhere between 1 and count is OK */
> > - if (!array_count || array_count > count)
> > + if (array_count > count)
> > return -EINVAL;
> >
> > group_fds = kcalloc(array_count, sizeof(*group_fds), GFP_KERNEL);
> > @@ -1358,7 +1358,7 @@ vfio_pci_ioctl_pci_hot_reset_groups(struct
> vfio_pci_core_device *vdev,
> > info.count = array_count;
> > info.files = files;
> >
> > - ret = vfio_pci_dev_set_hot_reset(vdev->vdev.dev_set, &info);
> > + ret = vfio_pci_dev_set_hot_reset(vdev->vdev.dev_set, &info, NULL);
> >
> > hot_reset_release:
> > for (file_idx--; file_idx >= 0; file_idx--)
> > @@ -1381,13 +1381,21 @@ static int vfio_pci_ioctl_pci_hot_reset(struct
> vfio_pci_core_device *vdev,
> > if (hdr.argsz < minsz || hdr.flags)
> > return -EINVAL;
> >
> > + /* zero-length array is only for cdev opened devices */
> > + if (!!hdr.count == vfio_device_cdev_opened(&vdev->vdev))
> > + return -EINVAL;
> > +
> > /* 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;
> >
> > - return vfio_pci_ioctl_pci_hot_reset_groups(vdev, hdr.count, slot, arg);
> > + if (hdr.count)
> > + return vfio_pci_ioctl_pci_hot_reset_groups(vdev, hdr.count, slot, arg);
> > +
> > + return vfio_pci_dev_set_hot_reset(vdev->vdev.dev_set, NULL,
> > + vfio_iommufd_device_ictx(&vdev->vdev));
> > }
> >
> > static int vfio_pci_ioctl_ioeventfd(struct vfio_pci_core_device *vdev,
> > @@ -2354,13 +2362,16 @@ const struct pci_error_handlers
> vfio_pci_core_err_handlers = {
> > };
> > EXPORT_SYMBOL_GPL(vfio_pci_core_err_handlers);
> >
> > -static bool vfio_dev_in_groups(struct vfio_pci_core_device *vdev,
> > +static bool vfio_dev_in_groups(struct vfio_device *vdev,
> > struct vfio_pci_group_info *groups)
> > {
> > unsigned int i;
> >
> > + if (!groups)
> > + return false;
> > +
> > for (i = 0; i < groups->count; i++)
> > - if (vfio_file_has_dev(groups->files[i], &vdev->vdev))
> > + if (vfio_file_has_dev(groups->files[i], vdev))
> > return true;
> > return false;
> > }
> > @@ -2436,7 +2447,8 @@ static int vfio_pci_dev_set_pm_runtime_get(struct
> vfio_device_set *dev_set)
> > * get each memory_lock.
> > */
> > static int vfio_pci_dev_set_hot_reset(struct vfio_device_set *dev_set,
> > - struct vfio_pci_group_info *groups)
> > + struct vfio_pci_group_info *groups,
> > + struct iommufd_ctx *iommufd_ctx)
> > {
> > struct vfio_pci_core_device *cur_mem;
> > struct vfio_pci_core_device *cur_vma;
> > @@ -2466,11 +2478,38 @@ static int vfio_pci_dev_set_hot_reset(struct
> vfio_device_set *dev_set,
> > goto err_unlock;
> >
> > list_for_each_entry(cur_vma, &dev_set->device_list, vdev.dev_set_list) {
> > + bool owned;
> > +
> > /*
> > - * Test whether all the affected devices are contained by the
> > - * set of groups provided by the user.
> > + * Test whether all the affected devices can be reset by the
> > + * user.
> > + *
> > + * If called from a group opened device and the user provides
> > + * a set of groups, all the devices in the dev_set should be
> > + * contained by the set of groups provided by the user.
> > + *
> > + * If called from a cdev opened device and the user provides
> > + * a zero-length array, all the devices in the dev_set must
> > + * be bound to the same iommufd_ctx as the input iommufd_ctx.
> > + * If there is any device that has not been bound to any
> > + * iommufd_ctx yet, check if its iommu_group has any device
> > + * bound to the input iommufd_ctx. Such devices can be
> > + * considered owned by the input iommufd_ctx as the device
> > + * cannot be owned by another iommufd_ctx when its iommu_group
> > + * is owned.
> > + *
> > + * Otherwise, reset is not allowed.
> > */
> > - if (!vfio_dev_in_groups(cur_vma, groups)) {
> > + if (iommufd_ctx) {
> > + int devid = vfio_iommufd_device_hot_reset_devid(&cur_vma-
> >vdev,
> > + iommufd_ctx);
> > +
> > + owned = (devid != VFIO_PCI_DEVID_NOT_OWNED);
> > + } else {
> > + owned = vfio_dev_in_groups(&cur_vma->vdev, groups);
> > + }
> > +
> > + if (!owned) {
> > ret = -EINVAL;
> > goto err_undo;
> > }
> > diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> > index 70cc31e6b1ce..f753124e1c82 100644
> > --- a/include/uapi/linux/vfio.h
> > +++ b/include/uapi/linux/vfio.h
> > @@ -690,6 +690,9 @@ enum {
> > * affected devices are represented in the dev_set and also owned by
> > * the user. This flag is available only when
> > * flag VFIO_PCI_HOT_RESET_FLAG_DEV_ID is set, otherwise reserved.
> > + * When set, user could invoke VFIO_DEVICE_PCI_HOT_RESET with a zero
> > + * length fd array on the calling device as the ownership is validated
> > + * by iommufd_ctx.
> > *
> > * Return: 0 on success, -errno on failure:
> > * -enospc = insufficient buffer, -enodev = unsupported for device.
> > @@ -721,6 +724,17 @@ struct vfio_pci_hot_reset_info {
> > * VFIO_DEVICE_PCI_HOT_RESET - _IOW(VFIO_TYPE, VFIO_BASE + 13,
> > * struct vfio_pci_hot_reset)
> > *
> > + * Userspace requests hot reset for the devices it operates. Due to the
> > + * underlying topology, multiple devices can be affected in the reset
> > + * while some might be opened by another user. To avoid interference
> > + * the calling user must ensure all affected devices are owned by itself.
>
> This phrasing suggest to me that we're placing the responsibility on
> the user to avoid resetting another user's devices.

This responsibility is not new. Is it? 😊

> Perhaps these
> paragraphs could be replaced with:
>
> A PCI hot reset results in either a bus or slot reset which may affect
> other devices sharing the bus/slot. The calling user must have
> ownership of the full set of affected devices as determined by the
> VFIO_DEVICE_GET_PCI_HOT_RESET_INFO ioctl.
>
> When called on a device file descriptor acquired through the vfio
> group interface, the user is required to provide proof of ownership
> of those affected devices via the group_fds array in struct
> vfio_pci_hot_reset.
>
> When called on a direct cdev opened vfio device, the flags field of
> struct vfio_pci_hot_reset_info reports the ownership status of the
> affected devices and this ioctl must be called with an empty group_fds
> array. See above INFO ioctl definition for ownership requirements.
>
> Mixed usage of legacy groups and cdevs across the set of affected
> devices is not supported.

Above is better.

> Other than this and the couple other comments, the series looks ok to
> me. We still need acks from Jason for iommufd on 3-5. Thanks,

Thanks, perhaps one more version after getting feedback from Jason.

Regards,
Yi Liu

> Alex
>
> > + *
> > + * As the ownership described by VFIO_DEVICE_GET_PCI_HOT_RESET_INFO, the
> > + * cdev opened devices must exclusively provide a zero-length fd array and
> > + * the group opened devices must exclusively use an array of group fds for
> > + * proof of ownership. Mixed access to devices between cdev and legacy
> > + * groups are not supported by this interface.
> > + *
> > * Return: 0 on success, -errno on failure.
> > */
> > struct vfio_pci_hot_reset {