Re: Looking for examples of vhost-user backends using VHOST_USER_SLAVE_IOTLB_MSG

Re: Looking for examples of vhost-user backends using VHOST_USER_SLAVE_IOTLB_MSG

[Alex Bennée]

Alex Bennée <alex.bennee@linaro.org> writes:

(apologies, empty reply to see if qemu-devel accepts this)

> Hi,
>
> As part of looking at implementing vhost-user daemons which don't have
> complete access to a guests address space we noticed the vhost-user spec
> has a definition for VHOST_USER_SLAVE_IOTLB_MSG's. Specifically the
> message VHOST_IOTLB_ACCESS_FAIL looks like it could be used to delegate
> the mapping of memory by the master/frontend so the backend can access
> it.
>
> As far as I can see no backends currently use this message and the
> specific handling of VHOST_IOTLB_ACCESS_FAIL in QEMU doesn't do much
> more than report an error.
>
> The VHOST_IOTLB_MISS does have some handling but the commentary seems to
> imply this is needed for the in kernel vhost kernel support (perhaps
> when real hardware is filling in a buffer being forwarded to a VirtIO
> device?).
>
> Can anyone point to any backends that implement these messages?
>
> We have implemented a Xen Vhost User Frontend:
>
>   https://github.com/vireshk/xen-vhost-frontend
>
> which currently uses a lightly hacked Xen privcmd device to map all of
> the guests memory. We want to investigate using the stricter gntdev
> device where buffers for individual transactions can be mapped into the
> backend domains before being released at the end of the transaction. We
> want to keep the hypervisor specific code in the frontend so the backend
> can stay portable between different hypervisors.
>
> Thanks,


-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro