linux-kernel - Re: [patch] x86, pat: fix reserve

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Message-ID: <20090109231316.GE6472@linux-os.sc.intel.com>
Date:	Fri, 9 Jan 2009 15:13:16 -0800
From:	Suresh Siddha <suresh.b.siddha@...el.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"tvignaud@...driva.com" <tvignaud@...driva.com>
Subject: Re: [patch] x86, pat: fix reserve_memtype() for legacy 1MB range

On Fri, Jan 09, 2009 at 02:55:55PM -0800, H. Peter Anvin wrote:
> Suresh Siddha wrote:
> > On Fri, Jan 09, 2009 at 02:39:31PM -0800, H. Peter Anvin wrote:
> >> Suresh Siddha wrote:
> >>> Here X is trying to map first 8KB of memory using /dev/mem. Existing
> >>> code treats first 0-4KB of memory as non-RAM and 4KB-8KB as RAM. Recent
> >>> code changes don't allow to map memory with different attributes
> >>> at the same time.
> >>>
> >> Why was 0-4 KB marked as non-RAM?  It is most definitely RAM, and should
> >> be WB.
> > 
> > While in reality it is RAM, we have CONFIG_STRICT_DEVMEM which doesn't allow
> > apps to map RAM pages using /dev/mem. And to allow app's to map the
> > legacy 0-4KB bios data page, we consider it as non-RAM.
> 
> Permission to map and memory type should not be connected.  Just to 
> clarify, when mapped, was it still WB?

yes it is. It's just treated and tracked differently.
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