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From: "Thomas Hellström" <>
To: Linux Kernel <>
Subject: Support for i386 PATs
Date: Sat, 27 Jan 2007 10:20:18 +0100	[thread overview]
Message-ID: <> (raw)


Does anybody have a strong opinion against adding support for
i386 Page Attribute Tables?

The main benefit would be that one can have write-combining memory
regions without setting up MTRRs. This will come in handy for a
device we're working with where the device driver needs to allocate the
display memory directly from system memory, and it may be difficult to fit
the mtrr alignment constraints.

The PAT may be set up at boot time with fixed backwards-compatible
memory types for the different PAT entries + defines like the following:

#define _PAGE_PAT_WB   xxx
#define _PAGE_PAT_WT   xxx
#define _PAGE_PAT_UC0 xxx
#define _PAGE_PAT_UC1 xxx
#define _PAGE_PAT_WC   xxx

which can be used in parallel with the old _PAGE_PWT and _PAGE_PCD bits.

The idea is that new memory types, WC for example, will use the pat entries
7 downto 4, whereas 0-3 are left to boot setting to maintain backwards 

1) The _PAGE_BIT_PAT will be the same as _PAGE_PSE, and _PAGE_PROTNONE.
As I understand it, _PAGE_PROTNONE is not used when the page is present, 
so this might not be an issue.
What about _PAGE_PSE?

2) The PATs need to be setup for each processor just after system boot.
Where is the best place to do this?

/Thomas Hellström

             reply	other threads:[~2007-01-27  9:20 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-01-27  9:20 Thomas Hellström [this message]
2007-01-27  9:33 ` Avi Kivity
2007-01-28 21:48 ` Dave Jones
2007-01-30 15:50   ` Thomas Hellström
2007-01-27 10:59 Mikael Pettersson
2007-01-28  7:54 ` H. Peter Anvin

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