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

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Date:	Tue, 13 Apr 2010 14:08:21 -0700
From:	Yinghai <yinghai.lu@...cle.COM>
To:	Bjorn Helgaas <bjorn.helgaas@...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 04/13/2010 02:02 PM, Bjorn Helgaas wrote:
> 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?

looks that file could be dropped.

We already put 0xa0000 - 0x100000 to reserved region.

> 
>> 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?

yes.

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

Thanks

Yinghai
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