[PATCH] [v2] x86: update memory map about hypervisor-reserved area

[PATCH] [v2] x86: update memory map about hypervisor-reserved area

[Dave Hansen]

changes from v1:
 * fix the actual address since the reserved area is larger than
   the guard hole

--

From: Dave Hansen <dave.hansen@linux.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@linux.intel.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: x86@kernel.org
Cc: linux-mm@kvack.org
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.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	2014-09-18 12:43:55.672230059 -0700
+++ b/Documentation/x86/x86_64/mm.txt	2014-09-18 12:55:17.642795338 -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 - ffff87ffffffffff (=43 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
_

[tip:x86/mm] x86/mm: Update memory map description to list hypervisor-reserved area

[tip-bot for Dave Hansen]

Commit-ID:  beb9147e95a75f41c984d7235cf6d59f3ca2d5db
Gitweb:     http://git.kernel.org/tip/beb9147e95a75f41c984d7235cf6d59f3ca2d5db
Author:     Dave Hansen <dave.hansen@linux.intel.com>
AuthorDate: Thu, 18 Sep 2014 12:56:06 -0700
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 19 Sep 2014 12:48:02 +0200

x86/mm: Update memory map description to list hypervisor-reserved area

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@linux.intel.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Link: http://lkml.kernel.org/r/20140918195606.841389D2@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 Documentation/x86/x86_64/mm.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Documentation/x86/x86_64/mm.txt b/Documentation/x86/x86_64/mm.txt
index afe68dd..052ee64 100644
--- a/Documentation/x86/x86_64/mm.txt
+++ b/Documentation/x86/x86_64/mm.txt
@@ -5,7 +5,7 @@ Virtual memory map with 4 level page tables:
 
 0000000000000000 - 00007fffffffffff (=47 bits) user space, different per mm
 hole caused by [48:63] sign extension
-ffff800000000000 - ffff80ffffffffff (=40 bits) guard hole
+ffff800000000000 - ffff87ffffffffff (=43 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