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Message-ID: <alpine.LFD.1.10.0808290827110.3300@nehalem.linux-foundation.org>
Date: Fri, 29 Aug 2008 08:31:08 -0700 (PDT)
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Ingo Molnar <mingo@...e.hu>
cc: Yinghai Lu <yhlu.kernel@...il.com>,
Thomas Gleixner <tglx@...utronix.de>,
"H. Peter Anvin" <hpa@...or.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Jesse Barnes <jbarnes@...tuousgeek.org>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: split e820 reserved entries record to late v4
On Fri, 29 Aug 2008, Ingo Molnar wrote:
> >
> > 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?
Correct.
> I thought it would only succeed if the new resource was smaller than (a
> subset of) the existing resource.
No, that's "request_resource()".
Yeah, I know, the resource code is complicated, and I wish it wasn't, but
the whole issue with nesting resources correctly simply _is_ fairly
complex.
So "insert_resource()" literally tries to fit a resource into an existing
tree, at the right level, whatever level that is.
In contrast, "request_resource()" is about exclusivity, and tries to
request a "leaf" resource - and it refuses to work if there are resources
it clashes with that cover the same range.
> In the other direction, when a newly inserted resource is a superset of
> the existing resource, i thought we'd fail.
For request_resource, yes.
> 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
Now THAT is somethign that the resource structs simply cannot handle. At
that point you'd get a failure even from insert_resource(), because it no
longer nests in the tree. You would have to split the range in order for
it to nest properly.
Linus
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