Re: [PATCH 5/8] xen/i386: make sure initial VGA/ISA mappings are not overridden

Jeremy Fitzhardinge
2009-05-08T15:08:59Z

Ingo Molnar wrote:
> * Jeremy Fitzhardinge <jeremy@goop.org> wrote:
>
>
>> From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
>>
>> arch/x86/mm/init_32.c overrides the ISA/VGA mappings with direct mappings
>> which do not have _PAGE_IOMAP set, thereby making the ISA space inaccessible.
>>
>> This patch adds to the existing hack to make sure the
>> pre-constructed ISA mappings are not incorrectly overwritten.
>>
>> This makes 32-bit dom0 VGA work properly.
>>
>
> I'm wondering, should we add this fix to .30 as well, is there any
> relevancy beyond dom0?
>

No, it only matters if the ISA region is mapping real hardware. For
domU we set up a set of dummy maps for ISA to mop up any stray
references, but they have no connection to underlying hardware.

This area is all a bit ugly, and I hope to ultimately address it by
making 32 and 64-bit use the same code for setting up the kernel
mappings (as the 64-bit code doesn't try to double-map the ISA area).

>> Thanks to Gerd Hoffman for pointing this out.
>>
>
> Please add Reported-by lines in such cases. That way not only does
> the reporting get reported prominently, but the tip-bot will Cc:
> Gerd too on the commit notification too. (which will sometimes spur
> further comments - while a commit hidden somewhere might not)
>

OK. I guess Diagnosed-by: would be the most appropriate tag in this case.

>> Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
>>
>
> Please also add impact-footers to all commits you queue up, if you
> want me to pull your tree directly. I can only guess at the impact
> of this one, is it:
>
> [ Impact: fix dom0-Xen-guest boot crash ]
>
> or:
>
> [ Impact: fix dom0-Xen-guest non-working VGA console ]
>
> ?
>
> (Please look at latest tip/master for examples about various impact
> lines, their precise format, and what we try to describe in them and
> how.)
>

OK, they're footers now?

Do you want me to respin these patches and repost?

J