Subject: [PATCH} x86, kdump: auto set crashkernel low size

Current code does not set low range for crashkernel if
the user does not specify that.

That cause regressions on system that does not support
intel_iommu properly.

Chao said his system does work well on 3.8 without extra parameter.
and iommu does not work with kdump.

Set low automatically if the user does not specify that.

For system that does support IOMMU with kdump properly, user could
specify crashkernel_low=0 to save that 72M low ram.

Reported-by: WANG Chao <chaowang@redhat.com>
Signed-off-by: Yinghai Lu <yinghai@kernel.org>

---
 arch/x86/kernel/setup.c |   15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

Index: linux-2.6/arch/x86/kernel/setup.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/setup.c
+++ linux-2.6/arch/x86/kernel/setup.c
@@ -521,19 +521,28 @@ static void __init reserve_crashkernel_l
 	unsigned long long low_base = 0, low_size = 0;
 	unsigned long total_low_mem;
 	unsigned long long base;
+	bool auto_set = false;
 	int ret;
 
 	total_low_mem = memblock_mem_size(1UL<<(32-PAGE_SHIFT));
 	ret = parse_crashkernel_low(boot_command_line, total_low_mem,
 						&low_size, &base);
-	if (ret != 0 || low_size <= 0)
-		return;
+	if (ret != 0) {
+		/* default swiotlb size and overflow: 64M + 8M */
+		low_size = 72UL << 20;
+		auto_set = true;
+	} else {
+		/* passed with crashkernel_low=0 ? */
+		if (!low_size)
+			return;
+	}
 
 	low_base = memblock_find_in_range(low_size, (1ULL<<32),
 					low_size, alignment);
 
 	if (!low_base) {
-		pr_info("crashkernel low reservation failed - No suitable area found.\n");
+		if (!auto_set)
+			pr_info("crashkernel low reservation failed - No suitable area found.\n");
 
 		return;
 	}