Re: [PATCH RFC 00/15] vhost-user: isolated memory

On 2026/07/24 7:29, ConKite wrote:
> This patch series implements a memory isolation mode in vhost-user. The
> purpose of this mode is to provide the option of additional security by
> eliminating direct access of guest memory by vhost-user devices.
> At a high level this works by:
> 
> 1. Adding qdev and qapi properties required to enable isolation mode for
>     various devices.
> 2. Allocating an isolation memory region in an anonymous file and mapping it
>     to host memory.  This isolation region will hold the bounce buffers and
>     vrings necessary to move data.
> 3. Using a vhost-iova-tree to allocate and track the mapping between
>     guest regions and their corresponding bounce buffers in the isolation
>     memory.
> 4. Creating shadow virtqueues to intercept request notifications.  As
>     kick and call events are received by an svq, it copies buffer
>     contents and descriptors between isolation and guest memory before
>     notifying the backend or guest.
> 
> Note: This project is currently in a partially functional state. For
> example, in testing vhost-user-input and a keyboard, keystrokes may
> register correctly or be double counted depending on the combination
> of backend daemon and guest OS used. However, the desire is to make
> this work public at this stage for comment on the overall
> approach.

I guess this intends to achieve something similar to IOMMU and also 
Linux's swiotlb for the VMM (please correct me if I'm wrong):

 > Other edge case scenarios arise for bounce buffers. For example, when
 > IOMMU mappings are set up for a DMA operation to/from a device that is
 > considered “untrusted”, the device should be given access only to the
 > memory containing the data being transferred. But if that memory
 > occupies only part of an IOMMU granule, other parts of the granule may
 > contain unrelated kernel data. Since IOMMU access control is
 > per-granule, the untrusted device can gain access to the unrelated
 > kernel data. This problem is solved by bounce buffering the DMA
 > operation and ensuring that unused portions of the bounce buffers do
 > not contain any unrelated kernel data.

https://docs.kernel.org/next/core-api/swiotlb.html#usage-scenarios

It would be nice if the security property this feature provides is 
explicitly stated, ideally as documentation.

I also hope this could fix vhost-user for TCG:
https://gitlab.com/qemu-project/qemu/-/work_items/2092

Perhaps the memory isolation should be enabled by default for TCG.

Implementation-wise, there are rough edges as you stated. Some of them 
can be fixed by more closely following what vhost-user does for the 
non-isolated case and what vhost-vdpa does with shadow virtqueues.

Regards,
Akihiko Odaki

> 
> Signed-off-by: Connor Kite <[email protected]>
> ---
> ConKite (2):
>        vhost-user: Consolidate chardev property definitions
>        vhost-user: Add memory-isolation qdev property to vhost-user devices
> 
> Connor Kite (13):
>        backends/cryptodev-vhost-user: add memory isolation bool
>        net/vhost-user: add memory isolation
>        vhost-user: add memory_isolation to VhostUserState
>        util/iova-tree: g_tree_foreach wrapper
>        hw/virtio: iova_tree_foreach wrapper
>        hw/virtio/vhost-shadow-virtqueue: used handler
>        hw/virtio/vhost-shadow-virtqueue: specified vring placement
>        hw/virtio/vhost-shadow-virtqueue: range boundary in translation
>        hw/virtio/vhost-user: create isolation region
>        hw/virtio/vhost-user: send isolation regions to device
>        hw/virtio/vhost-user: add shadow virtqueues and eventfd intercepts
>        hw/virtio/vhost-user: handle data movement with shadow vqs
>        hw/virtio/vhost-user: shadow vq cleanup
> 
>   backends/cryptodev-vhost-user.c      |  24 +-
>   backends/vhost-user.c                |   4 +-
>   hw/block/vhost-user-blk.c            |   4 +-
>   hw/display/vhost-user-gpu.c          |   4 +-
>   hw/scsi/vhost-user-scsi.c            |   4 +-
>   hw/virtio/vhost-iova-tree.c          |  15 ++
>   hw/virtio/vhost-iova-tree.h          |   3 +
>   hw/virtio/vhost-shadow-virtqueue.c   |  30 ++-
>   hw/virtio/vhost-shadow-virtqueue.h   |  17 ++
>   hw/virtio/vhost-stub.c               |   3 +-
>   hw/virtio/vhost-user-base.c          |  13 +-
>   hw/virtio/vhost-user-fs.c            |   4 +-
>   hw/virtio/vhost-user-gpio.c          |   4 -
>   hw/virtio/vhost-user-i2c.c           |   5 -
>   hw/virtio/vhost-user-input.c         |   5 -
>   hw/virtio/vhost-user-rng.c           |   5 -
>   hw/virtio/vhost-user-rtc.c           |   4 -
>   hw/virtio/vhost-user-scmi.c          |   4 +-
>   hw/virtio/vhost-user-snd.c           |   1 -
>   hw/virtio/vhost-user-spi.c           |   5 -
>   hw/virtio/vhost-user-test-device.c   |   1 -
>   hw/virtio/vhost-user-vsock.c         |   4 +-
>   hw/virtio/vhost-user.c               | 441 ++++++++++++++++++++++++++++++++++-
>   include/hw/virtio/vhost-user-base.h  |   1 +
>   include/hw/virtio/vhost-user-blk.h   |   1 +
>   include/hw/virtio/vhost-user-fs.h    |   1 +
>   include/hw/virtio/vhost-user-scmi.h  |   1 +
>   include/hw/virtio/vhost-user-vsock.h |   1 +
>   include/hw/virtio/vhost-user.h       |   6 +-
>   include/hw/virtio/virtio-gpu.h       |   1 +
>   include/hw/virtio/virtio-scsi.h      |   1 +
>   include/qemu/iova-tree.h             |  13 ++
>   include/system/vhost-user-backend.h  |   3 +-
>   net/passt.c                          |  16 +-
>   net/vhost-user.c                     |  11 +-
>   qapi/net.json                        |  15 +-
>   qapi/qom.json                        |   6 +-
>   util/iova-tree.c                     |   5 +
>   38 files changed, 622 insertions(+), 64 deletions(-)
> ---
> base-commit: 006a22cb26998998385b104db1ff9466ef2f3153
> change-id: 20260604-vhost-user-isolated-memory-070ed4833ee7
> 
> Best regards,