Re: [Xen-devel] [PATCH 04/19] xen: arm: provide and use a handle_raz_wi helper

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Thu, 2015-04-02 at 16:14 +0100, Julien Grall wrote:
> Hi Ian,
> 
> On 31/03/2015 11:07, Ian Campbell wrote:
> > Reduces the use of goto in the trap handlers to none.
> >
> > Some explcitily 32-bit types become register_t here, but that's OK, on
> 
> s/explcitily/explicitly/
> 
> > 32-bit they are 32-bit already and on 64-bit it is fine/harmless to
> > set the larger register, a 32-bit guest won't see the top half in any
> > case.
> 
> What about 32-bit userspace on 64-bit kernel? Are we sure that a guest 
> kernel won't only save the bottom half of the register?

That would be fine, since the userspace couldn't see the top half anyway
so not saving it doesn't hurt.

In any case, the trap here has been talking from 32-bit mode and that is
where we will return, so I'm not sure the guest kernel enters the
picture, does it?

Ian.


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