Re: [PATCH v3] x86/boot: skip realmode init code when running as Xen PV guest

[Juergen Gross <jgross@xxxxxxxx>]

On 24.11.22 14:28, Borislav Petkov wrote:
> On Wed, Nov 23, 2022 at 12:45:23PM +0100, Juergen Gross wrote:
> > When running as a Xen PV guest there is no need for setting up the
> > realmode trampoline, as realmode isn't supported in this environment.
> >
> > Trying to setup the trampoline has been proven to be problematic in
> > some cases, especially when trying to debug early boot problems with
> > Xen requiring to keep the EFI boot-services memory mapped (some
> > firmware variants seem to claim basically all memory below 1M for boot
> > services).
> >
> > Introduce new x86_platform_ops operations for that purpose, which can
> > be set to a nop by the Xen PV specific kernel boot code.
> >
> > Fixes: 084ee1c641a0 ("x86, realmode: Relocator for realmode code")
> This text and Fixes: tag sounds like this needs to go to Linus and
> stable now?
Looking at the date when 084ee1c641a0 went in I don't think it _needs_
to go in now, but I wouldn't complain ...

> > diff --git a/arch/x86/realmode/init.c b/arch/x86/realmode/init.c
> > index 41d7669a97ad..247aca9f8ed1 100644
> > --- a/arch/x86/realmode/init.c
> > +++ b/arch/x86/realmode/init.c
> > @@ -200,14 +200,18 @@ static void __init set_real_mode_permissions(void)
> >         set_memory_x((unsigned long) text_start, text_size >> PAGE_SHIFT);
> >   }
> >   
> > -static int __init init_real_mode(void)
> > +void __init init_real_mode(void)
> >   {
> >         if (!real_mode_header)
> >                 panic("Real mode trampoline was not allocated");
> >   
> >   	setup_real_mode();
> >         set_real_mode_permissions();
> > +}
> >   
> > +static int __init call_init_real_mode(void)
> > +{
> > +       x86_platform.realmode_init();
> >         return 0;
> >   }
> > -early_initcall(init_real_mode);
> > +early_initcall(call_init_real_mode);
> I'll name that one "do_init_real_mode" as "call init" sounds weird.
Fine with me.

> Otherwise, it is as straightforward as it gets.
Thanks,


Juergen

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