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

[Juergen Gross]

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);
  }

+void __init init_real_mode(void)
  {
        if (!real_mode_header)
                panic("Real mode trampoline was not allocated");

        set_real_mode_permissions();
+}

+{
+       x86_platform.realmode_init();
        return 0;
  }
-early_initcall(init_real_mode);
+early_initcall(call_init_real_mode);

-static int __init init_real_mode(void) setup_real_mode(); +static int __init call_init_real_mode(void)

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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