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

[Prabhakar Kushwaha]

On Mon, Dec 23, 2019 at 8:57 PM Chen Zhou <chenzhou10@xxxxxxxxxx> 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@xxxxxxxxxx>
> ---
>  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?

--pk