Re: [Xen-devel] [PATCH 4/5] xen: introduce XEN_GUEST_HANDLE_PARAM

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2012-08-06 at 16:43 +0100, Jan Beulich wrote:
> >>> On 06.08.12 at 16:12, Stefano Stabellini 
> >>> <stefano.stabellini@xxxxxxxxxxxxx> wrote:
> > Note: this change does not make any difference on x86 and ia64.
> > 
> > 
> > XEN_GUEST_HANDLE_PARAM is going to be used to distinguish guest pointers
> > stored in memory from guest pointers as hypercall parameters.
> 
> I have to admit that really dislike this, to a large part because of
> the follow up patch that clutters the corresponding function
> declarations even further. Plus I see no mechanism to convert
> between the two, yet I can't see how - long term at least - you
> could get away without such conversion.
> 
> Is it really a well thought through and settled upon decision to
> make guest handles 64 bits wide even on 32-bit ARM? After all,
> both x86 and PPC got away without doing so

Well, on x86 we have the compat XLAT layer, which is a pretty complex
piece of code, so "got away without" is a bit strong... We'd really
rather not have to have a non-trivial compat layer on arm too by having
the struct layouts be the same on 32/64.

Ian.



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