[v2,0/2] vhost-vdpa: Add support for NO-IOMMU mode

Message

Srujana Challa Sept. 20, 2024, 2:05 p.m. UTC

This patchset introduces support for an UNSAFE, no-IOMMU mode in the
vhost-vdpa driver. When enabled, this mode provides no device isolation,
no DMA translation, no host kernel protection, and cannot be used for
device assignment to virtual machines. It requires RAWIO permissions
and will taint the kernel.

This mode requires enabling the "enable_vhost_vdpa_unsafe_noiommu_mode"
option on the vhost-vdpa driver and also negotiate the feature flag
VHOST_BACKEND_F_NOIOMMU. This mode would be useful to get
better performance on specifice low end machines and can be leveraged
by embedded platforms where applications run in controlled environment.

First patch introduces a module parameter
"enable_vhost_vdpa_unsafe_noiommu_mode", while the second patch
introduces a feature flag VHOST_BACKEND_F_NOIOMMU to the vhost vdpa
driver to support NO-IOMMU mode.

This feature flag indicates to userspace that the driver can safely
operate in NO-IOMMU mode. If the flag is not present, userspace should
assume NO-IOMMU mode is unsupported and must not proceed.

v1->v2:
- Introduced new feature flag to vhost backend features for negotiating
  NO-IOMMU feature.

Srujana Challa (2):
  vhost-vdpa: introduce module parameter for no-IOMMU mode
  vhost-vdpa: introduce NO-IOMMU backend feature bit

 drivers/vhost/vdpa.c             | 39 +++++++++++++++++++++++++++++++-
 include/uapi/linux/vhost_types.h |  2 ++
 2 files changed, 40 insertions(+), 1 deletion(-)