Re: [Xen-devel] 32-on-64: pvfb issue

[Markus Armbruster <armbru@xxxxxxxxxx>]

Gerd Hoffmann <kraxel@xxxxxxx> writes:

>   Hi,
>
> There is a problem with the virtual framebuffer: The page directory in
> the shared page (xenfb_page->pd[]) is unsigned long and thus has
> different sizes on 32bit and 64bit.  The alignment is different too. And
> on top of that the frontend driver doesn't clear the shared page, which
> makes it difficult to autodetect the bitsize.  I've tried nevertheless,
> patch (untested!) attached for comments.  In the long run this code is
> supposed to be replaced by grant tables anyway, so it is probably okay
> to live with the hack for the time being.  We could of course also fix
> the struct if we can afford breaking the interface.  As it is quite new
> and probably (hmm, does fc6 ship it?) not widely used yet that might be
> an option.

Breaking the API now is right out of the question, I fear :)

You can evolve the API.  Let the frontend put something in xenstore[*]
that lets the backend detect which page layout to use.  Make sure the
backend can deal with old and new frontend.  I doubt it's worthwhile
here.

Excuse my ignorance, but why do you have to guess the guest's size?
Doesn't dom0 know?


[*] I suggested to put version ID right into the page, but that was
shot down in favor of xenstore.

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