linux-kernel - Re: [PATCH] Prevent reserving RAM in the region already reserved by BIOS

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Message-ID: <AANLkTikYcu6fM3yLoYIZOGZXgsRUfCgJeWS51Sjo-Fny@mail.gmail.com>
Date:	Wed, 19 May 2010 15:58:33 -0700
From:	Mathieu Rondonneau <mathieu.rondonneau@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Yinghai <yinghai.lu@...cle.com>, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] Prevent reserving RAM in the region already reserved by 
	BIOS

Thanks for the feedback.

No, I don' t see any changes in the /proc/iomem.

I am trying to prevent a ioremap of a 4K size on a non aligned 4K
address that is below the ISA_START_ADDRESS.

The problem generates a oops about overlapping.
I have a fix which instruct to not to do any re-map if the section
name is "reserved".
Which is not really clean.
I am looking for a clean way to tell the ioremap function to not remap
bios reserved memory.
That' s why I thought the e820 would be a good start.

I will continue looking into this. It does not crash the systems. A
warning generates the oops.

-Mathieu


On Wed, May 19, 2010 at 10:43 AM, H. Peter Anvin <hpa@...or.com> wrote:
> On 05/19/2010 10:40 AM, Yinghai wrote:
>> On 05/18/2010 10:35 PM, Mathieu Rondonneau wrote:
>>> Does it make sense to prevent looking for stolen RAM below the ISA section.
>>>
>>>
>>> Signed-off-by: Mathieu Rondonneau <mathieu.rondonneau@...il.com>
>>> ---
>>>  arch/x86/kernel/e820.c |    2 ++
>>>  1 files changed, 2 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
>>> index 7bca3c6..322c9c3 100644
>>> --- a/arch/x86/kernel/e820.c
>>> +++ b/arch/x86/kernel/e820.c
>>> @@ -1156,6 +1156,8 @@ void __init e820_reserve_resources_late(void)
>>>                         end = MAX_RESOURCE_SIZE;
>>>                 if (start >= end)
>>>                         continue;
>>> +               if (end < ISA_START_ADDRESS)
>>> +                       continue;
>>>                 printk(KERN_DEBUG "reserve RAM buffer: %016llx - %016llx ",
>>>                                start, end);
>>>                 reserve_region_with_split(&iomem_resource, start, end,
>>
>> do you notice any changes in /proc/iomem?
>>
>
> It should be harmless to reserve memory which is already reserved, so
> this patch is at best a no-op.  Furthermore, it introduces another
> instance of special address space (ISA_START_ADDRESS in this case) which
> is never a good thing.
>
>        -hpa
>
>
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