[PATCH 3/3] x86/crash: Allocate enough low memory when crashkernel=high

[Borislav Petkov]

From: Joerg Roedel <jroedel@xxxxxxx>

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>
Acked-by: Baoquan He <bhe@xxxxxxxxxx>
Cc: Baoquan He <bhe@xxxxxxxxxx>
Cc: Dave Young <dyoung@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: JÃrg RÃdel <joro@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
Cc: kexec@xxxxxxxxxxxxxxxxxxx
Cc: x86-ml <x86@xxxxxxxxxx>
Link: http://lkml.kernel.org/r/1433500202-25531-4-git-send-email-joro@xxxxxxxxxx
[ Reflow comment. ]
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
---
 arch/x86/kernel/setup.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index d74ac33290ae..5a697e56634c 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -531,12 +531,15 @@ 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 ? */
-- 
2.3.5

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