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Re: [PATCH v2 2/5] x86/vga: fix mapping of the VGA text buffer
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 18 Mar 2025 15:28:32 +0100
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- Cc: Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Tue, 18 Mar 2025 14:28:41 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 18.03.2025 14:11, Andrew Cooper wrote:
> On 18/03/2025 9:19 am, Roger Pau Monne wrote:
>> The call to ioremap_wc() in video_init() will always fail, because
>> video_init() is called ahead of vm_init_type(), and so the underlying
>> __vmap() call will fail to allocate the linear address space.
>>
>> Fix by reverting to the previous behavior and using ioremap() for the VGA
>> text buffer.
>>
>> Fixes: 81d195c6c0e2 ('x86: introduce ioremap_wc()')
>> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>
> This is somewhat ugly.
>
> ioremap() isn't really any better than ioremap_wc(); this only works
> because plain ioremap() has a special case for the bottom 1M where it
> does nothing and exits.
And this is exactly why I screwed up back then. Imo we would be better
off moving to using __va() directly here. Otherwise the same mistake
could be made again by someone (perhaps even me) noticing the less
efficient ioremap(), when ioremap_wc() really would be wanted.
Jan
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