[Discussion] Xen grants and access permissions

[Viresh Kumar <viresh.kumar@xxxxxxxxxx>]

Hi Oleksandr,

As you already know, I am looking at how we can integrate the Xen
grants work in our implementation of Rust based Xen vhost frontend [1].

The hypervisor independent vhost-user backends [2] talk to
xen-vhost-frontend using the standard vhost-user protocol [3]. Every
memory region that the backends get access to are sent to it by the
frontend as memory region descriptors, which contain only address and
size information and lack any permission flags.

I noticed that with Xen grants, there are strict memory access
restrictions, where a memory region may be marked READ only and we
can't map it as RW anymore, trying that just fails. Because the
standard vhost-user protocol doesn't have any permission flags, the
vhost libraries (in Rust) can't do anything else but try to map
everything as RW.

I am wondering how do I proceed on this as I am very much stuck here.

-- 
viresh

[1] https://github.com/vireshk/xen-vhost-frontend
[2] https://github.com/rust-vmm/vhost-device
[3] https://qemu.readthedocs.io/en/latest/interop/vhost-user.html
[4] 
https://qemu.readthedocs.io/en/latest/interop/vhost-user.html#memory-regions-description