On Mar 7, 2020, at 5:06 AM, Chen Zhou [off-list ref] wrote:



On 2020/3/5 18:13, Prabhakar Kushwaha wrote:

quoted

On Mon, Dec 23, 2019 at 8:57 PM Chen Zhou [off-list ref] wrote:

quoted

Crashkernel=X tries to reserve memory for the crash dump kernel under
4G. If crashkernel=X,low is specified simultaneously, reserve spcified
size low memory for crash kdump kernel devices firstly and then reserve
memory above 4G.

Signed-off-by: Chen Zhou <redacted>
---
arch/arm64/kernel/setup.c |  8 +++++++-
arch/arm64/mm/init.c      | 31 +++++++++++++++++++++++++++++--
2 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
index 56f6645..04d1c87 100644
--- a/arch/arm64/kernel/setup.c
+++ b/arch/arm64/kernel/setup.c

@@ -238,7 +238,13 @@ static void __init request_standard_resources(void)
                   kernel_data.end <= res->end)
                       request_resource(res, &kernel_data);

#ifdef CONFIG_KEXEC_CORE
-               /* Userspace will find "Crash kernel" region in /proc/iomem. */
+               /*
+                * Userspace will find "Crash kernel" region in /proc/iomem.
+                * Note: the low region is renamed as Crash kernel (low).
+                */
+               if (crashk_low_res.end && crashk_low_res.start >= res->start &&
+                               crashk_low_res.end <= res->end)
+                       request_resource(res, &crashk_low_res);
               if (crashk_res.end && crashk_res.start >= res->start &&
                   crashk_res.end <= res->end)
                       request_resource(res, &crashk_res);

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index b65dffd..0d7afd5 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c

@@ -80,6 +80,7 @@ static void __init reserve_crashkernel(void)

{
       unsigned long long crash_base, crash_size;
       int ret;
+       phys_addr_t crash_max = arm64_dma32_phys_limit;

       ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(),
                               &crash_size, &crash_base);

@@ -87,12 +88,38 @@ static void __init reserve_crashkernel(void)
       if (ret || !crash_size)
               return;

+       ret = reserve_crashkernel_low();
+       if (!ret && crashk_low_res.end) {
+               /*
+                * If crashkernel=X,low specified, there may be two regions,
+                * we need to make some changes as follows:
+                *
+                * 1. rename the low region as "Crash kernel (low)"
+                * In order to distinct from the high region and make no effect
+                * to the use of existing kexec-tools, rename the low region as
+                * "Crash kernel (low)".
+                *
+                * 2. change the upper bound for crash memory
+                * Set MEMBLOCK_ALLOC_ACCESSIBLE upper bound for crash memory.
+                *
+                * 3. mark the low region as "nomap"
+                * The low region is intended to be used for crash dump kernel
+                * devices, just mark the low region as "nomap" simply.
+                */
+               const char *rename = "Crash kernel (low)";
+
+               crashk_low_res.name = rename;
+               crash_max = MEMBLOCK_ALLOC_ACCESSIBLE;
+               memblock_mark_nomap(crashk_low_res.start,
+                                   resource_size(&crashk_low_res));
+       }
+
       crash_size = PAGE_ALIGN(crash_size);

       if (crash_base == 0) {
               /* Current arm64 boot protocol requires 2MB alignment */
-               crash_base = memblock_find_in_range(0, arm64_dma32_phys_limit,
-                               crash_size, SZ_2M);
+               crash_base = memblock_find_in_range(0, crash_max, crash_size,
+                               SZ_2M);
               if (crash_base == 0) {
                       pr_warn("cannot allocate crashkernel (size:0x%llx)\n",
                               crash_size);
--

I tested this patch series on ARM64-ThunderX2 with no issue with
bootargs crashkenel=X@Y crashkernel=250M,low

$ dmesg | grep crash
[    0.000000] crashkernel reserved: 0x0000000b81200000 -
0x0000000c81200000 (4096 MB)
[    0.000000] Kernel command line:
BOOT_IMAGE=/boot/vmlinuz-5.6.0-rc4+
root=UUID=866b8df3-14f4-4e11-95a1-74a90ee9b694 ro
crashkernel=4G@0xb81200000 crashkernel=250M,low nowatchdog earlycon
[   29.310209]     crashkernel=250M,low

$  kexec -p -i /boot/vmlinuz-`uname -r`
--initrd=/boot/initrd.img-`uname -r` --reuse-cmdline
$ echo 1 > /proc/sys/kernel/sysrq ; echo c > /proc/sysrq-trigger

But when i tried with crashkernel=4G crashkernel=250M,low as bootargs.
Kernel is not able to allocate memory.
[    0.000000] cannot allocate crashkernel (size:0x100000000)
[    0.000000] Kernel command line:
BOOT_IMAGE=/boot/vmlinuz-5.6.0-rc4+
root=UUID=866b8df3-14f4-4e11-95a1-74a90ee9b694 ro crashkernel=4G
crashkernel=250M,low nowatchdog
[   29.332081]     crashkernel=250M,low

does crashkernel=X@Y mandatory to get allocated beyond 4G?
am I missing something?

   crashkernel=4G

   You need to look at the memory map on node 0  from dmesg     ( or /proc/iomem ) to determine if there is any memory in that range  - 0x100000000 == 1st byte above 4G .

On the Arm server class machines  I’ve seen the 1st usable memory range above 4G is 32G area. It is platform dependent where the 1st range is. 

I can't reproduce the problem in my environment, can you test with other size,
such as "crashkernel=1G crashkernel=250M,low", see if there is the same issue.

Besides, crashkernel=X@Y isn't mandatory to get allocated beyond 4G,
can you show the whole file /proc/iomem.

Thanks,
Chen Zhou

quoted

--pk

.

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