Re: [Q] Guest mode in HVM

[rkuo@codeaurora.org]

On Tue, Mar 5, 2013 at 11:45 AM, <cotulla@yandex.ru> wrote:
> I have a question:
> Did I understand right that "HVM Guest mode" is actually native hexagon
> user mode?
> And native hexagon super mode is only used inside HVM during trap1 and
> exception handlers?

On certain versions of the architecture, yes, it effectively is pushed
into user mode.

> It's not possible to specify access mode for user/super mode in TLB.
> ...
> We are going to emulate separate memory access attributes (RWX) for linux
> kernel and linux user modes by using two different ASIDs for user and
> kernel mode per hw thread.

Right, the supervisor isn't subject to RWX bits, but it is still subject
to ASIDs.  I think there was some other nuance to the fault handling, but
that was the gist of it.

This brings us to hypervisors which we've sort of skirted in other emails.
 There will be changes in the Hexagon architecture from one version to
another, some of which will affect the guest operation and compatibility. 
Long term, "we" would like to have Linux just deal with the hypervisor
interface.

Of course, that isn't useful to anybody without the actual hypervisor.  We
recognize this and are working hard to try to release some version of a
functioning hypervisor for the community to continue tinkering with.  If
we get that out, perhaps that will be more preferable for you to work
on...

That said, I think it's great that you all are motivated enough to go for
a bare metal port in the first place (and it looks like you've made great
progress).  I see no reason to reject bare metal patches, but we would
need to keep things clean with ifdefs/config switches...


Thanks,
Richard Kuo


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