Re: RT Xen on ARM - R-Car series

["Roger Pau Monné" <roger.pau@citrix.com>]

On Thu, Feb 07, 2019 at 11:42:16AM +0200, Andrii Anisov wrote:
> Hello All,
> 
> On 06.02.19 23:03, Stefano Stabellini wrote:
> > That's great. Could you or Roger take care of cleaning up the patch and
> > properly submitting it to the list?
> 
> I can take it for cleaning up.
> 
> > And also double check that it won't
> > break any guests (at least the ones we know about: Linux and Windows on
> > x86).
> 
> I'm not sure I could properly check it for x86. For sure can't do that for windows guest.

I've been thinking about this with other Citrix folks, and I'm not
sure the proposed patch is a good solution. It's not possible for us
to know whether there's a kernel somewhere relying on changing the
virtual address of the runtime state area without issuing a new
hypercall.

If such kernel existed by making this change we would introduce random
memory corruption to that kernel, which would be very hard to track
and considered a regression.

I think the best way to move forward is to pick my patch and introduce
a new hypercall that instead of a virtual address takes a guest
physical address. Will you be OK with this Andrii?

Note that the Linux kernel would also need to be modified to make use
of this new hypercall, but that's likely close to a 1 line change.

Thanks, Roger.

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