vhost_iotlb: bound map allocation in add_range

vhost_iotlb_add_range_ctx() only retires an old entry when the table
has a non-zero limit, has exactly reached that limit and has
VHOST_IOTLB_FLAG_RETIRE set. Non-retiring tables can keep allocating
entries after reaching their configured limit.

Existing vhost devices allocate their IOTLB with max_iotlb_entries from
vhost.c, which defaults to 2048 and is tunable by module parameter. Use
the caller-provided limit at the allocation point instead of adding a
separate default in the common IOTLB helper, and reject non-positive
values in vhost paths that can report an error.

Other vhost IOTLB users should not create zero-limit tables when entries
can be populated from userspace or guest-controlled requests. Add
caller-side max_iotlb_entries parameters for mlx5 vDPA, VDUSE and
vhost-vDPA. Reject non-positive VDUSE and vhost-vDPA values, and require
at least two entries for vdpa_sim and mlx5 vDPA paths that install
full-range mappings, since those mappings are split into two IOTLB
entries.

Handle full-range mappings in the common helper by checking that the
IOTLB can hold both split entries before inserting the first half. This
avoids returning an error after leaving a half mapping behind.

When the table is full, keep the existing retire behavior for retiring
tables and return -ENOSPC for non-retiring tables. Reuse the retired map
node instead of freeing it and allocating a replacement, so a stream of
IOTLB updates cannot keep forcing GFP_ATOMIC allocations after the table
has reached its limit. If a zero-limit IOTLB still reaches the common
helper, treat it as a configuration error and return -EINVAL.

I found this bug myself, though the patch was written with AI assistance.

Fixes: 0bbe30668d89 ("vhost: factor out IOTLB")
Assisted-by: OpenAI-Codex:GPT-5
Signed-off-by: Linfeng Sun <linfeng.sun.dev@gamil.com>
Message-ID: <AMYAtgAiKmgYcSQT5ukl-4qq.3.1781960405943.Hmail.241270009@hdu.edu.cn>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

0 files changed, 0 insertions, 0 deletions