Re: [PATCH v7 2/4] arm64: kdump: reserve crashkenel above 4G for crash dump kernel

[Chen Zhou <chenzhou10@huawei.com>]

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?

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
> 
> .
>