Re: [Xen-devel] [RFC v1 6/8] x86/init: use linker table for i386 early setup

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Tue, Dec 15, 2015 at 02:16:35PM -0800, Luis R. Rodriguez wrote:
> From: "Luis R. Rodriguez" <mcgrof@xxxxxxxx>
> 
> This also annotates this is only used for PC and
> lguest hardware subarchitectures.
> 
> Signed-off-by: Luis R. Rodriguez <mcgrof@xxxxxxxx>

On Xen the code path (before this patch) was:
xen_start_kernel->i386_start_kernel->i386_default_early_setup

and now you remove the i386_default_early_setup call?

The mpparse.setup_ioapic_ids is irrelevant as under Xen code it
does:

709                 /* Avoid searching for BIOS MP tables */
1710                 x86_init.mpparse.find_smp_config = x86_init_noop;
1711                 x86_init.mpparse.get_smp_config = x86_init_uint_noop;

Great, MP tables is completly ignored.


The next one : i386_reserve_resources

Looks to be reserving VGA RAM .. which is a bit pointless when you
have no legacy devices.

The reserve_standard_io_resources means the /proc/ioport is smaller now.

Actually looking under an PV guest it is:

# cat /proc/ioports 
0000-001f : dma1
0020-0021 : pic1
0040-0043 : timer0
0050-0053 : timer1
0060-0060 : keyboard
0064-0064 : keyboard
0070-0071 : rtc_cmos
0080-008f : dma page reg
00a0-00a1 : pic2
00c0-00df : dma2
00f0-00ff : fpu
# cat /proc/iomem
00000000-00000fff : reserved
00001000-0009ffff : System RAM
000a0000-000fffff : reserved

Which means /proc/ioports won't have anything in it (with your change)


And /proc/iomem will have the  000a0000-000fffff region available (maybe?)
Ah no. We mark it as reserved in the early part of boot:

[    0.000000] Xen: [mem 0x00000000000a0000-0x00000000000fffff] reserved

I am curious - what does your kernel run as PV look like?

Thanks.

> ---
>  arch/x86/kernel/head32.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kernel/head32.c b/arch/x86/kernel/head32.c
> index 768fa3888066..1db8eec5b0e2 100644
> --- a/arch/x86/kernel/head32.c
> +++ b/arch/x86/kernel/head32.c
> @@ -21,12 +21,15 @@
>  #include <asm/bootparam_utils.h>
>  #include <asm/x86_init.h>
>  
> -static void __init i386_default_early_setup(void)
> +static void __init i386_set_setup_funcs(void)
>  {
>       /* Initialize 32bit specific setup functions */
>       x86_init.resources.reserve_resources = i386_reserve_resources;
>       x86_init.mpparse.setup_ioapic_ids = setup_ioapic_ids_from_mpc;
>  }
> +x86_init_early(BIT(X86_SUBARCH_PC) |
> +            BIT(X86_SUBARCH_LGUEST),
> +            NULL, NULL, i386_set_setup_funcs);
>  
>  asmlinkage __visible void __init i386_start_kernel(void)
>  {
> @@ -41,9 +44,6 @@ asmlinkage __visible void __init i386_start_kernel(void)
>       case X86_SUBARCH_CE4100:
>               x86_ce4100_early_setup();
>               break;
> -     default:
> -             i386_default_early_setup();
> -             break;
>       }
>  
>       x86_init_fn_init_tables();
> -- 
> 2.6.2
> 

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