[PATCH v6 0/3] vhost: fix device IOTLB feature lifecycle

[Jia Jia <physicalmtea@gmail.com>]

Both vhost-vsock and vhost-net can leave the device IOTLB attached when
userspace clears VIRTIO_F_ACCESS_PLATFORM. They can also replace an
existing IOTLB with a new empty table when a later feature update keeps
ACCESS_PLATFORM enabled, for example when updating logging.

When the IOTLB mode changes, the vring addresses previously supplied by
userspace no longer have the same address-space meaning. Leaving those
addresses installed would allow an old IOVA to be used as a direct
userspace address after the IOTLB is detached.

This series invalidates the vring access state during IOTLB transitions,
makes IOTLB initialization idempotent, and uses a common teardown helper
for vhost-vsock and vhost-net. IOTLB mode changes are applied even while a
virtqueue backend is attached. The device-wide IOTLB is dropped first, each
virtqueue then clears its IOTLB pointer and cached ring access under its own
mutex, and the old table is freed only after every virtqueue has completed
the handoff.

A successful live mode change leaves the backend attached but invalidates
the cached vring addresses. Userspace must configure the vring addresses for
the new address mode before data processing can resume. When
ACCESS_PLATFORM is enabled, the usual IOTLB miss/update protocol repopulates
the new table.

Changes since v5:
- invalidate desc, avail, used, logging state, and metadata on IOTLB
  transitions;
- apply IOTLB mode changes while a backend is attached, following the
  per-virtqueue handoff suggested in review;
- apply the IOTLB teardown to vhost-net as well as vhost-vsock.

Jia Jia (3):
  vhost: invalidate vring access on IOTLB transitions
  vhost/vsock: discard IOTLB when ACCESS_PLATFORM is cleared
  vhost/net: discard IOTLB when ACCESS_PLATFORM is cleared

 drivers/vhost/net.c   |  8 ++++++--
 drivers/vhost/vhost.c | 53 ++++++++++++++++++++++++++++++++++++++++-
 drivers/vhost/vhost.h |  1 +
 drivers/vhost/vsock.c | 10 ++++++---
 4 files changed, 66 insertions(+), 6 deletions(-)