linux-kernel - [PATCH] x86: update memory map about hypervisor-reserved area

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Message-Id: <20140918154621.F16A2C86@viggo.jf.intel.com>
Date:	Thu, 18 Sep 2014 08:46:21 -0700
From:	Dave Hansen <dave@...1.net>
To:	linux-kernel@...r.kernel.org
Cc:	Dave Hansen <dave@...1.net>, dave.hansen@...ux.intel.com,
	ryabinin.a.a@...il.com, dvyukov@...gle.com, andi@...stfloor.org,
	x86@...nel.org, linux-mm@...ck.org, tglx@...utronix.de,
	mingo@...hat.com
Subject: [PATCH] x86: update memory map about hypervisor-reserved area


From: Dave Hansen <dave.hansen@...ux.intel.com>

Peter Anvin says:
> 0xffff880000000000 is the lowest usable address because we have
> agreed to leave 0xffff800000000000-0xffff880000000000 for the
> hypervisor or other non-OS uses.

Let's call this out in the documentation.

This came up during the kernel address sanitizer discussions
where it was proposed to use this area for other kernel things.

Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Andrey Ryabinin <ryabinin.a.a@...il.com>
Cc: Dmitry Vyukov <dvyukov@...gle.com>
Cc: Andi Kleen <andi@...stfloor.org>
Cc: x86@...nel.org
Cc: linux-mm@...ck.org
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
---

 b/Documentation/x86/x86_64/mm.txt |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff -puN Documentation/x86/x86_64/mm.txt~update-x86-mm-doc Documentation/x86/x86_64/mm.txt
--- a/Documentation/x86/x86_64/mm.txt~update-x86-mm-doc	2014-09-17 21:44:10.499781092 -0700
+++ b/Documentation/x86/x86_64/mm.txt	2014-09-17 21:44:31.852740822 -0700
@@ -5,7 +5,7 @@ Virtual memory map with 4 level page tab
 
 0000000000000000 - 00007fffffffffff (=47 bits) user space, different per mm
 hole caused by [48:63] sign extension
-ffff800000000000 - ffff80ffffffffff (=40 bits) guard hole
+ffff800000000000 - ffff80ffffffffff (=40 bits) guard hole, reserved for hypervisor
 ffff880000000000 - ffffc7ffffffffff (=64 TB) direct mapping of all phys. memory
 ffffc80000000000 - ffffc8ffffffffff (=40 bits) hole
 ffffc90000000000 - ffffe8ffffffffff (=45 bits) vmalloc/ioremap space
_
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