linux-kernel - Re: [PATCH] x86/pci: make pci_mem

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Message-ID: <20090416165640.GA13927@elte.hu>
Date:	Thu, 16 Apr 2009 18:56:40 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Yinghai Lu <yinghai@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-pci@...r.kernel.org, yannick.roehlly@...e.fr
Subject: Re: [PATCH] x86/pci: make pci_mem_start to be aligned only -v3

* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Thu, 16 Apr 2009, Jesse Barnes wrote:
> > 
> > Any comments on this one, Linus?  Should I include your ack?
> 
> I'm not ready to ack it, no. I don't think the suggested patch is very 
> clean or necessarily sensible as-is. It seems very ad-hoc. 
> 
> I was literally thinking of something like 
>  "round up from the last RAM by X"
>  "round up from the last reserved region by Y"
>  "pick the bigger of the two"
> 
> with helper functions for the two cases and comments along the 
> lines of why we do it. Something that was a bit more obvious about 
> what it's doing and why.

That's sensible - but i'd also like to inject hpa's add-on idea: if 
we do that then we should do it _explicitly_ and _visibly_, by 
injecting an artificial e820 reservation range to all expected 
"vulnerable" holes we cannot fully trust.

We'd do that after all the fixed resources are allocated, but before 
dynamic PCI allocations.

That prevents the PCI layer from dynamically allocating anything 
into that protective zone, and documents it as well (and makes it 
visible in boot logs, etc.) - instead of just a silent rule 
somewhere that no-one will really see if it breaks.

Or would this be a bad idea for some obvious reason i missed?

	Ingo
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