[tip:x86/boot] x86/debug: Extend the lower bound of crash kernel low reservations

From: tip-bot for Jiri Bohac
Date: Thu Jun 22 2017 - 07:14:53 EST

Commit-ID: fe2d48b805d01e14ddb8144de01de43171eb516f
Gitweb: http://git.kernel.org/tip/fe2d48b805d01e14ddb8144de01de43171eb516f
Author: Jiri Bohac <jbohac@xxxxxxx>
AuthorDate: Fri, 16 Jun 2017 18:16:02 +0200
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 22 Jun 2017 11:10:23 +0200

x86/debug: Extend the lower bound of crash kernel low reservations

The following change in 2013:

0212f9159694 ("x86: Add Crash kernel low reservation")

... introduced reserve_crashkernel_low(). This function is used to
reserve crash kernel memory either if crashkernel=size,low is given
on the command line or if the region reserved by reserve_crashkernel
is entirely above 4G.

reserve_crashkernel_low() tries to find a block of 'low_size' bytes.
But there seems to be no good reason to restrict the lower bound
of the range to 'low_size'.

Make memblock_find_in_range() search from the start of memory.

Signed-off-by: Jiri Bohac <jbohac@xxxxxxx>
Cc: Eric Biederman <ebiederm@xxxxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Yinghai Lu <yinghai@xxxxxxxxxx>
Link: http://lkml.kernel.org/r/20170616161602.2r7birrf2y3ylv6v@xxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
arch/x86/kernel/setup.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 0b4d3c6..848d048 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -503,7 +503,7 @@ static int __init reserve_crashkernel_low(void)
return 0;

- low_base = memblock_find_in_range(low_size, 1ULL << 32, low_size, CRASH_ALIGN);
+ low_base = memblock_find_in_range(0, 1ULL << 32, low_size, CRASH_ALIGN);
if (!low_base) {
pr_err("Cannot reserve %ldMB crashkernel low memory, please try smaller size.\n",
(unsigned long)(low_size >> 20));