Re: [PATCH v2 2/5] x86/vga: fix mapping of the VGA text buffer

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Tue, Mar 18, 2025 at 03:28:32PM +0100, Jan Beulich wrote:
> 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.

I can switch to using __va(), that's fine.  I guess we should then
remove the special casing for the low 1MB in ioremap()?

Thanks, Roger.