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 that his system does work well on 3.8 without extra parameter.
even iommu does not work with kdump.

Set crashkernel_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.

-v3: add swiotlb_size() according to Konrad.

Reported-by: WANG Chao <chaow...@redhat.com>
Tested-by: WANG Chao <chaow...@redhat.com>
Signed-off-by: Yinghai Lu <ying...@kernel.org>

---
 arch/x86/kernel/setup.c |   15 ++++++++++++---
 include/linux/swiotlb.h |    1 +
 lib/swiotlb.c           |   19 +++++++++++++++----
 3 files changed, 28 insertions(+), 7 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
@@ -522,19 +522,28 @@ 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) {
+               /* swiotlb size and etc 8M */
+               low_size = swiotlb_size_or_default() + (8UL<<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;
        }
Index: linux-2.6/include/linux/swiotlb.h
===================================================================
--- linux-2.6.orig/include/linux/swiotlb.h
+++ linux-2.6/include/linux/swiotlb.h
@@ -25,6 +25,7 @@ extern int swiotlb_force;
 extern void swiotlb_init(int verbose);
 int swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose);
 extern unsigned long swiotlb_nr_tbl(void);
+unsigned long swiotlb_size_or_default(void);
 extern int swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs);
 
 /*
Index: linux-2.6/lib/swiotlb.c
===================================================================
--- linux-2.6.orig/lib/swiotlb.c
+++ linux-2.6/lib/swiotlb.c
@@ -105,9 +105,9 @@ setup_io_tlb_npages(char *str)
        if (!strcmp(str, "force"))
                swiotlb_force = 1;
 
-       return 1;
+       return 0;
 }
-__setup("swiotlb=", setup_io_tlb_npages);
+early_param("swiotlb", setup_io_tlb_npages);
 /* make io_tlb_overflow tunable too? */
 
 unsigned long swiotlb_nr_tbl(void)
@@ -115,6 +115,18 @@ unsigned long swiotlb_nr_tbl(void)
        return io_tlb_nslabs;
 }
 EXPORT_SYMBOL_GPL(swiotlb_nr_tbl);
+
+/* default to 64MB */
+#define IO_TLB_DEFAULT_SIZE (64UL<<20)
+unsigned long swiotlb_size_or_default(void)
+{
+       unsigned long size;
+
+       size = io_tlb_nslabs << IO_TLB_SHIFT;
+
+       return size ? size : (IO_TLB_DEFAULT_SIZE);
+}
+
 /* Note that this doesn't work with highmem page */
 static dma_addr_t swiotlb_virt_to_bus(struct device *hwdev,
                                      volatile void *address)
@@ -188,8 +200,7 @@ int __init swiotlb_init_with_tbl(char *t
 void  __init
 swiotlb_init(int verbose)
 {
-       /* default to 64MB */
-       size_t default_size = 64UL<<20;
+       size_t default_size = IO_TLB_DEFAULT_SIZE;
        unsigned char *vstart;
        unsigned long bytes;
 
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