Re: [PATCH 1/5] arm64: kdump: reserve memory for crash dump kernel

From: Pratyush Anand
Date: Fri Apr 10 2015 - 02:37:18 EST

On Friday 10 April 2015 11:27 AM, AKASHI Takahiro wrote:
Hi Pratyush,

On 04/09/2015 10:09 PM, Pratyush Anand wrote:
Hi Takahiro,

On Thursday 26 March 2015 01:58 PM, AKASHI Takahiro wrote:
Crash dump kernel will access memory regions in system kernel via
copy_oldmem_page(), which reads a page with ioremap'ing it assuming that
such pages are not part of main memory of crash dump kernel.
This is true under non-UEFI environment because kexec-tools modifies
a device tree adding "usablemem" attributes to memory sections.
Under UEFI, however, this is not true because UEFI remove memory
in a device tree and export all the memory regions, even though they
to system kernel.

So we should add "mem=X[MG]" boot parameter to limit the meory size and
avoid hitting the following assertion in ioremap():
if (WARN_ON(pfn_valid(__phys_to_pfn(phys_addr))))
return NULL;

Well I am using your updated kexec-tool which has support of automatic
addition of "mem=" parameter. I found that this
warning is still appearing and therefore another error about "Kdump:
vmcore not initialized".

Memory address for which ioremap failed was almost at the top of
crash_reserved_mem. So I modified kexec-tool [1] to
accept user specific mem= parameter with a value lesser than physical
location which was being remapped, however still
the warning was there.

Further I noticed that there is no reserved memblock with nonzero
memblock_region->size when early_mem ->
memblock_enforce_memory_limit is called. Therefore this mem= param is
not limiting memory location in my case.

On crash dump kernel? Sounds strange.
Can you send me the followings for both 1st kernel and crash dump kernel?
(add memblock_debug to cmd line for verbose messages)

- boot log (dmesg)
- cat /proc/iomem

sending them in a private mail is fine.


I was just wondering, why do not we use ioremap_cache instead of
ioremap in copy_oldmem_page?

Good point.
My next version of kdump patch uses ioremap_cache() for another reason.

Thanks that you have already changed it. I am using ioremap_cache and I am able to get /proc/vmcore :)
ioremap allocates VAs with memory attribute DEVICE which might not be correct for RAM area.ioremap_cache is using memory attribute NORMAL which seems more logical for RAM areas.

# As I'm discussing with Mark about kvm issue, I'm holding off
submitting it.

I am using one more modification on top of your patches for finding crashkernel address automatically. If that seems fine to you then may be I can send you that patch and you can add that in your next rev.

Author: Pratyush Anand <panand@xxxxxxxxxx>
Date: Tue Apr 7 08:14:55 2015 +0530

arm64/kdump: Find free area for crash kernel memory

If crashkernel=X@0 is passed to the kernel then this patch will find
free memory area of size X for crash kernel.

Signed-off-by: Pratyush Anand <panand@xxxxxxxxxx>

diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
index 94694897beea..90b0b9d138f6 100644
--- a/arch/arm64/kernel/setup.c
+++ b/arch/arm64/kernel/setup.c
@@ -368,10 +368,18 @@ static void __init reserve_crashkernel(void)
if (ret)

- ret = memblock_reserve(crash_base, crash_size);
- if (ret < 0) {
+ /* 0 means: find the address automatically */
+ if (crash_base <= 0) {
+ crash_base = memblock_alloc(crash_size, 2 << 20);
+ if (!crash_base) {
+ pr_warn("Could not find free memory for crashkernel\n");
+ return;
+ }
+ } else if (memblock_reserve(crash_base, crash_size) < 0) {
pr_warn("crashkernel reservation failed - memory is in use (0x%lx)\n",
- (unsigned long)crash_base);
+ (unsigned long)crash_base);

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