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SubjectRe: [PATCH v7 2/4] arm64: kdump: reserve crashkenel above 4G for crash dump kernel
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> On Mar 7, 2020, at 5:06 AM, Chen Zhou <chenzhou10@huawei.com> wrote:
>
>
>
> On 2020/3/5 18:13, Prabhakar Kushwaha wrote:
>> On Mon, Dec 23, 2019 at 8:57 PM Chen Zhou <chenzhou10@huawei.com> wrote:
>>>
>>> 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 <chenzhou10@huawei.com>
>>> ---
>>> 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
>
>>
>> --pk
>>
>> .
>>
>
>
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