linux-kernel - Re: [PATCH -v2 1/2] x86: Reserve [0xa0000, 0x100000] in e820 map

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Date:	Tue, 13 Apr 2010 15:02:07 -0600
From:	Bjorn Helgaas <bjorn.helgaas@...com>
To:	Yinghai <yinghai.lu@...cle.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Andy Isaacson <adi@...apodia.org>, guenter.roeck@...csson.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Renninger <trenn@...e.de>
Subject: Re: [PATCH -v2 1/2] x86: Reserve [0xa0000, 0x100000] in e820 map

On Mon, 2010-04-12 at 15:32 -0700, Yinghai wrote:
> Update e820 at first, and later put them resource tree.
> 
> -V2: reserved that early, no PCI BAR can use it, force them to get new one
> 
> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
> Cc: Guenter Roeck <guenter.roeck@...csson.com>
> Cc: Andy Isaacson <adi@...apodia.org>
> Tested-by: Andy Isaacson <adi@...apodia.org>
> Cc: Bjorn Helgaas <bjorn.helgaas@...com>
> Acked-by: H. Peter Anvin <hpa@...or.com>
> 
> ---
>  arch/x86/include/asm/setup.h |    1 -
>  arch/x86/kernel/head32.c     |    1 -
>  arch/x86/kernel/setup.c      |   19 +------------------
>  3 files changed, 1 insertion(+), 20 deletions(-)
> 
> Index: linux-2.6/arch/x86/include/asm/setup.h
> ===================================================================
> --- linux-2.6.orig/arch/x86/include/asm/setup.h
> +++ linux-2.6/arch/x86/include/asm/setup.h
> @@ -44,7 +44,6 @@ static inline void visws_early_detect(vo
>  extern unsigned long saved_video_mode;
>  
>  extern void reserve_standard_io_resources(void);
> -extern void i386_reserve_resources(void);
>  extern void setup_default_timer_irq(void);
>  
>  #ifdef CONFIG_X86_MRST
> Index: linux-2.6/arch/x86/kernel/head32.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/kernel/head32.c
> +++ linux-2.6/arch/x86/kernel/head32.c
> @@ -22,7 +22,6 @@ static void __init i386_default_early_se
>  {
>  	/* Initilize 32bit specific setup functions */
>  	x86_init.resources.probe_roms = probe_roms;
> -	x86_init.resources.reserve_resources = i386_reserve_resources;
>  	x86_init.mpparse.setup_ioapic_ids = setup_ioapic_ids_from_mpc;
>  
>  	reserve_ebda_region();

I like the fact that this makes x86_64 and x86_32 handle the legacy VGA
framebuffer the same way.

What about arch/x86/kernel/probe_roms_32.c?  That deals with expansion
ROMs in the 0xc0000-0xfffff range, including the VGA ROM.  We only build
it for x86_32; is that correct, or should it be unified, too?

> Index: linux-2.6/arch/x86/kernel/setup.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/kernel/setup.c
> +++ linux-2.6/arch/x86/kernel/setup.c
> @@ -693,7 +693,7 @@ static void __init trim_bios_range(void)
>  	 * area (640->1Mb) as ram even though it is not.
>  	 * take them out.
>  	 */
> -	e820_remove_range(BIOS_BEGIN, BIOS_END - BIOS_BEGIN, E820_RAM, 1);
> +	e820_add_region(BIOS_BEGIN, BIOS_END - BIOS_BEGIN, E820_RESERVED);

Let me see if I understand this.  On Andy's machine, the e820 map
doesn't mention the 0xa0000-0xf0000 range at all:

  BIOS-e820: 0000000000000000 - 000000000009ec00 (usable)
  BIOS-e820: 00000000000f0000 - 0000000000100000 (reserved)

e820_reserve_resources() inserts resources for some e820 entries (those
that start before 0x100000 or are not E820_RESERVED).  Andy's machine
didn't supply any e820 entries that cover 0xa0000-0xf0000, so we didn't
insert any resources there, and PCI assumed that range was available.

This patch adds the [0xa0000-0x100000] range as E820_RESERVED.  Since
that starts below 0x100000, e820_reserve_resources() will insert a
corresponding resource marked as BUSY.

Then the second patch prevents PCI from using that BUSY region to
allocate resources to devices.

Is my understanding correct?

I don't feel like I know enough about x86 architecture to ack this
patch, but I don't object to it.

Bjorn

>  	sanitize_e820_map(e820.map, ARRAY_SIZE(e820.map), &e820.nr_map);
>  }
>  
> @@ -1052,20 +1052,3 @@ void __init setup_arch(char **cmdline_p)
>  
>  	mcheck_init();
>  }
> -
> -#ifdef CONFIG_X86_32
> -
> -static struct resource video_ram_resource = {
> -	.name	= "Video RAM area",
> -	.start	= 0xa0000,
> -	.end	= 0xbffff,
> -	.flags	= IORESOURCE_BUSY | IORESOURCE_MEM
> -};
> -
> -void __init i386_reserve_resources(void)
> -{
> -	request_resource(&iomem_resource, &video_ram_resource);
> -	reserve_standard_io_resources();
> -}
> -
> -#endif /* CONFIG_X86_32 */

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