[PATCH 1/4] x86, kdump: Set crashkernel_low automatically

Yinghai Lu
2013-04-02T17:20:32Z

Chao said that kdump does does work well on his system on 3.8
without extra parameter, even iommu does not work with kdump.
And now have to append crashkernel_low=Y in first kernel to make
kdump work.

We have now modified crashkernel=X to allocate memory beyong 4G (if
available) and do not allocate low range for crashkernel if the user
does not specify that with crashkernel_low=Y. This causes regression
if iommu is not enabled. Without iommu, swiotlb needs to be setup in
first 4G and there is no low memory available to second kernel.

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.
-v4: add comments what 8M is for according to hpa.
also update more crashkernel_low= in kernel-parameters.txt
-v5: update changelog according to Vivek.

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

---
Documentation/kernel-parameters.txt | 15 ++++++++++++---
arch/x86/kernel/setup.c | 20 +++++++++++++++++---
include/linux/swiotlb.h | 1 +
lib/swiotlb.c | 19 +++++++++++++++----
4 files changed, 45 insertions(+), 10 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 +521,33 @@ 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) {
+ /*
+ * two parts from lib/swiotlb.c:
+ * swiotlb size: user specified with swiotlb= or default.
+ * swiotlb overflow buffer: now is hardcoded to 32k,
+ * round to 8M to cover more others.
+ */
+ 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;

Index: linux-2.6/Documentation/kernel-parameters.txt
===================================================================
--- linux-2.6.orig/Documentation/kernel-parameters.txt
+++ linux-2.6/Documentation/kernel-parameters.txt
@@ -596,9 +596,6 @@ bytes respectively. Such letter suffixes
is selected automatically. Check
Documentation/kdump/kdump.txt for further details.

- crashkernel_low=size[KMG]
- [KNL, x86] parts under 4G.
-
crashkernel=range1:size1[,range2:size2,...][@offset]
[KNL] Same as above, but depends on the memory
in the running system. The syntax of range is
@@ -606,6 +603,18 @@ bytes respectively. Such letter suffixes
a memory unit (amount[KMG]). See also
Documentation/kdump/kdump.txt for an example.

+ crashkernel_low=size[KMG]
+ [KNL, x86_64] range under 4G. When crashkernel= is
+ passed, kernel allocate physical memory region
+ above 4G, that cause second kernel crash on system
+ that need swiotlb later. Kernel would try to allocate
+ some region below 4G automatically. This one let
+ user to specify own low range under 4G for second
+ kernel instead.
+ 0: to disable low allocation on systems that do not
+ need swiotlb, that will save 72M low ram in first
+ kernel.
+
cs89x0_dma= [HW,NET]
Format: <dma>