[tip:x86/kdump] x86/crash: Allocate enough low memory when crashkernel=high

[tip-bot for Joerg Roedel]

Commit-ID:  94fb9334182284e8e7e4bcb9125c25dc33af19d4
Gitweb:     http://git.kernel.org/tip/94fb9334182284e8e7e4bcb9125c25dc33af19d4
Author:     Joerg Roedel <jroedel@xxxxxxx>
AuthorDate: Wed, 10 Jun 2015 17:49:42 +0200
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 11 Jun 2015 08:28:39 +0200

x86/crash: Allocate enough low memory when crashkernel=high

When the crash kernel is loaded above 4GiB in memory, the
first kernel allocates only 72MiB of low-memory for the DMA
requirements of the second kernel. On systems with many
devices this is not enough and causes device driver
initialization errors and failed crash dumps. Testing by
SUSE and Redhat has shown that 256MiB is a good default
value for now and the discussion has lead to this value as
well. So set this default value to 256MiB to make sure there
is enough memory available for DMA.

Signed-off-by: Joerg Roedel <jroedel@xxxxxxx>
[ Reflow comment. ]
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Acked-by: Baoquan He <bhe@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Dave Young <dyoung@xxxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: JÃrg RÃdel <joro@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
Cc: kexec@xxxxxxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/1433500202-25531-4-git-send-email-joro@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/kernel/setup.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index d74ac33..cba8288 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -531,12 +531,14 @@ static void __init reserve_crashkernel_low(void)
 	if (ret != 0) {
 		/*
 		 * two parts from lib/swiotlb.c:
-		 *	swiotlb size: user specified with swiotlb= or default.
-		 *	swiotlb overflow buffer: now is hardcoded to 32k.
-		 *		We round it to 8M for other buffers that
-		 *		may need to stay low too.
+		 * -swiotlb size: user-specified with swiotlb= or default.
+		 *
+		 * -swiotlb overflow buffer: now hardcoded to 32k. We round it
+		 * to 8M for other buffers that may need to stay low too. Also
+		 * make sure we allocate enough extra low memory so that we
+		 * don't run out of DMA buffers for 32-bit devices.
 		 */
-		low_size = swiotlb_size_or_default() + (8UL<<20);
+		low_size = max(swiotlb_size_or_default() + (8UL<<20), 256UL<<20);
 		auto_set = true;
 	} else {
 		/* passed with crashkernel=0,low ? */
--
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