Re: [Qemu-devel] [PATCH 0/3] Vhost: no more leak QEMU virtual addresses to user backend

[Maxime Coquelin <maxime.coquelin@redhat.com>]

On 12/21/2017 04:53 AM, Michael S. Tsirkin wrote:
> On Wed, Dec 20, 2017 at 04:07:41PM +0000, Stefan Hajnoczi wrote:
>> On Tue, Dec 19, 2017 at 07:11:26PM +0100, Maxime Coquelin wrote:
>>> Before this series, QEMU process virtual addresses are sent to the
>>> user backend as user addresses.
>>>
>>> Passing these virtual addresses aren't useful, as the backend doesn't
>>> direct access to QEMU address space.
>>>
>>> It does make sense however for kernel backend, which can access QEMU
>>> address space.
>>>
>>> This series introduce a new enum set by the backend stating whether it
>>> prefers using QEMU Virtual addresses or Guest physical addresses as
>>> User address, and make vhost-user backend to use Guest physical
>>> addresses.
>>>
>>> Maxime Coquelin (3):
>>>    vhost-user: rename VhostUserMemory userspace_addr field to user_addr
>>>    vhost: introduce backend's user address type
>>>    vhost-user: no more leak QEMU virtual addresses to user backend
>>>
>>>   hw/virtio/vhost-backend.c         |  1 +
>>>   hw/virtio/vhost-user.c            |  6 ++++--
>>>   hw/virtio/vhost.c                 | 16 ++++++++++++----
>>>   include/hw/virtio/vhost-backend.h |  6 ++++++
>>>   4 files changed, 23 insertions(+), 6 deletions(-)
>>>
>>> -- 
>>> 2.14.3
>>>
>>
>> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> 
> This makes make check fail. Any idea why?
> 

That's interesting, it fails because the rings aren't initialized with
vhost-user-test (even without my series, but we don't notice).

It fails in vhost_virtqueue_start(), because vq->desc is NULL.

Adding some debug prints shows that vq->desc_phys, vq->avail_phys and 
vq->used_phys are all 0 for both queues.

So when using QEMU VAs as user addresses, vq->desc, vq->used and
vq->avail are translated to a non-NULL address, and it doesn't fail.

Only the multiqueue test returns non-zero and different addresses
between the rings.

I'm looking into it.

Regards,
Maxime