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

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Date:	Fri, 29 Aug 2008 00:52:43 -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 Fri, Aug 29, 2008 at 12:28 AM, Ingo Molnar <mingo@...e.hu> wrote:
>
> * Yinghai Lu <yhlu.kernel@...il.com> wrote:
>
>> 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 ...
>
> yes, that sounds an excellent idea - i was thinking of something
> muchmore complex like breaking up the reserved entry - but indeed just
> creating a large enough superset should be perfect. I.e. extend both
> start and end until we fit fully. [or reach some natural boundary such
> as 0 or 4GB]
>
>> > 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
>
> btw., perhaps we should try this: first try a request_resource(). If
> that fails it means we overlap with something - then we should already
> printk a warning. (e820 reserved entries should never conflict with PCI
> resources, should they?)
>
> then try an insert_resource(). If that too fails it means a partial
> overlap - printk another warning. Try the extension (within reasonable
> limits) and retry.
>
> Does that sound worthwile?

request_resource should always fail at that case, because we are using
iomem_resource at first parent...

YH
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