linux-kernel - Re: [PATCH] x86: split e820 reserved entries record to late v4

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Message-ID: <86802c440808290016m6af6ecc7l52f5c7eca7f29a02@mail.gmail.com>
Date:	Fri, 29 Aug 2008 00:16:31 -0700
From:	"Yinghai Lu" <yhlu.kernel@...il.com>
To:	"Ingo Molnar" <mingo@...e.hu>
Cc:	"Thomas Gleixner" <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Jesse Barnes" <jbarnes@...tuousgeek.org>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: split e820 reserved entries record to late v4

On Thu, Aug 28, 2008 at 11:58 PM, Ingo Molnar <mingo@...e.hu> wrote:
>
> * Yinghai Lu <yhlu.kernel@...il.com> wrote:
>
>> >  BIOS-e820: 0000000077ff0000 - 0000000078000000 (reserved)
>> >  BIOS-e820: 00000000e0000000 - 00000000f0000000 (reserved)
>> >  BIOS-e820: 00000000fec00000 - 0000000100000000 (reserved)
>> >
>> > which overlaps with the chipset PCI BAR (hpet) resource:
>> >
>> >   pci 0000:00:14.0: BAR has HPET at fed00000-fed003ff
>> >
>> > so due to this 1K conflict we take the full e820-reserved entry out and
>> > give the range 0xfec00000-0x100000000 as 'free'.
>>
>> you will get
>> fec00000 - ffffffff reserved
>>    fed0000 - fed003ff hpet
>>      fed0000 - fed003ff 0000:00:14.0
>
> ok - because it's fully contained insert_resource() will succeed? I
> thought it would only succeed if the new resource was smaller than (a
> subset of) the existing resource. In the other direction, when a newly
> inserted resource is a superset of the existing resource, i thought we'd
> fail.
>
> hypothetical scenario, what if we had neither a superset nor a subset
> scenario, but a partial overlap, between:
>
>> >  BIOS-e820: 00000000fec00000 - 0000000100000000 (reserved)
>
> and:
>
>> >   pci 0000:00:14.0: BAR has HPET at feb0f000-fec01000
>
> i.e. we have:
>
>      [... PCI BAR ...]
>            [... e820 reservation ...]
>
> in that case the insert_resource() will fail due to the conflict. Can we
> declare it in that case that the e820 reserved entry is mortally broken
> and we just ignore it?

yes, that will fail to insert ...

expand to 0xfeb0f000 - 0xfffffff and try again.?

may need to update insert_resource to return conflict resource ...

>
> At least we should emit a prominent warning if insert_resource() fails,
> and add in an mdelay(2000) so that the user sees it.
right

YH
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