On 2/20/19 11:39 PM, Marek Marczykowski-Górecki wrote:
> On Wed, Feb 20, 2019 at 08:15:30PM +0000, Joao Martins wrote:
>> 2. PV Driver support (patches 17 - 39)
>>
>> We start by redirecting hypercalls from the backend to routines
>> which emulate the behaviour that PV backends expect i.e. grant
>> table and interdomain events. Next, we add support for late
>> initialization of xenbus, followed by implementing
>> frontend/backend communication mechanisms (i.e. grant tables and
>> interdomain event channels). Finally, introduce xen-shim.ko,
>> which will setup a limited Xen environment. This uses the added
>> functionality of Xen specific shared memory (grant tables) and
>> notifications (event channels).
>
> Does it mean backends could be run in another guest, similarly as on
> real Xen? AFAIK virtio doesn't allow that as virtio backends need
> arbitrary write access to guest memory. But grant tables provide enough
> abstraction to do that safely.
>
In this series not yet. Here we are trying to resemble how KVM drives its kernel
PV backends (i.e. vhost virtio).
The domU grant {un,}mapping could be added complementary. The main difference
between domU gntmap vs shim gntmap is that the former maps/unmaps the guest
page on the backend. Most of it is common code I think.
Joao
