linux-kernel - Re: [PATCH] x86: split e820 reserved entries record to late v2

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Date:	Thu, 28 Aug 2008 23:16:47 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Yinghai Lu <yhlu.kernel@...il.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	David Witbrodt <dawitbro@...global.net>,
	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 v2

* Yinghai Lu <yhlu.kernel@...il.com> wrote:

> +void __init e820_reserve_resources_late(void)
> +{
> +	int i;
> +	struct resource *res;
> +
> +	res = e820_res;
> +	for (i = 0; i < e820.nr_map; i++) {
> +		if (e820.map[i].type == E820_RESERVED && res->start >= (1ULL<<20))
> +			insert_resource(&iomem_resource, res);
> +		res++;
> +	}
> +}

Here we have the problem of overlap i outlined earlier: if there's a 
partial overlap at this stage (as i think it can happen in the hpet case 
on David's box), we wont insert the E820_RESERVED resource.

The hpet hang will be solved, because we dont reprogram the BAR, but we 
now keep the formerly e820-reserved area as 'free' - which the PCI code 
could allocate new resources into - which could cause other problems 
(hangs, non-working devices, etc.) down the line.

Which most likely wont happen currently in practice (there's enough free 
space elsewhere), but it's still a not truly 'free' area and it would be 
nice to have a complete and correct picture, based on all sources of 
information we have.

	Ingo
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