Subject: [PATCH v12 11/16] arm64: kdump: reserve memory for crash dump kernel

From: [email-masked] (AKASHI Takahiro)
Date: Wed, 16 Dec 2015 14:19:26 +0900

On 12/16/2015 02:29 AM, Will Deacon wrote:
> On Tue, Nov 24, 2015 at 10:25:34PM +0000, Geoff Levand wrote:
>> From: AKASHI Takahiro <[email-masked]>
>>
>> On primary kernel, the memory region used by crash dump kernel must be
>> specified by "crashkernel=" boot parameter. reserve_crashkernel()
>> will allocate and reserve the region for later use.
>>
>> User space tools will be able to find the region marked as "Crash kernel"
>> in /proc/iomem.
>>
>> Signed-off-by: AKASHI Takahiro <[email-masked]>
>> ---
>>   arch/arm64/kernel/setup.c |  7 +++++-
>>   arch/arm64/mm/init.c      | 54 +++++++++++++++++++++++++++++++++++++++++++++++
>>   2 files changed, 60 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
>> index 8119479..f9fffc9 100644
>> --- a/arch/arm64/kernel/setup.c
>> +++ b/arch/arm64/kernel/setup.c
>> @@ -31,7 +31,6 @@
>>   #include <linux/screen_info.h>
>>   #include <linux/init.h>
>>   #include <linux/kexec.h>
>> -#include <linux/crash_dump.h>
>>   #include <linux/root_dev.h>
>>   #include <linux/cpu.h>
>>   #include <linux/interrupt.h>
>> @@ -221,6 +220,12 @@ static void __init request_standard_resources(void)
>>   		    kernel_data.end <= res->end)
>>   			request_resource(res, &kernel_data);
>>   	}
>> +
>> +#ifdef CONFIG_KEXEC
>> +	/* User space tools will find "Crash kernel" region in /proc/iomem. */
>> +	if (crashk_res.end)
>> +		insert_resource(&iomem_resource, &crashk_res);
>> +#endif
>
> Why can't this bit be moved into reserved_crashkernel, at the end?

Because
- I want to call reserve_crashkernel() as early as possbile, (so before
   request_standard_resources()), and
- if inserting "Crash kernel" region is done before request_standard_resources(),
   request_resource() for "System RAM" region which contains "Crash kernel" will
   fail and the entry will be lost from /proc/iomem.

>>   }
>>
>>   #ifdef CONFIG_BLK_DEV_INITRD
>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>> index 17bf39a..24f0a1c 100644
>> --- a/arch/arm64/mm/init.c
>> +++ b/arch/arm64/mm/init.c
>> @@ -34,6 +34,7 @@
>>   #include <linux/dma-contiguous.h>
>>   #include <linux/efi.h>
>>   #include <linux/swiotlb.h>
>> +#include <linux/kexec.h>
>>
>>   #include <asm/fixmap.h>
>>   #include <asm/memory.h>
>> @@ -66,6 +67,55 @@ static int __init early_initrd(char *p)
>>   early_param("initrd", early_initrd);
>>   #endif
>>
>> +#ifdef CONFIG_KEXEC
>> +/*
>> + * reserve_crashkernel() - reserves memory for crash kernel
>> + *
>> + * This function reserves memory area given in "crashkernel=" kernel command
>> + * line parameter. The memory reserved is used by dump capture kernel when
>> + * primary kernel is crashing.
>> + */
>> +static void __init reserve_crashkernel(void)
>> +{
>> +	unsigned long long crash_size = 0, crash_base = 0;
>> +	int ret;
>> +
>> +	ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(),
>> +				&crash_size, &crash_base);
>> +	if (ret)
>> +		return;
>
> What's the point in ret?

parse_crashkernel() will returns -EINVAL if
- the boot command line doesn't contain "crashkernel=" parameter, or
- "crashkernel=" parameter has an invalid synstax of value
Otherwise returns 0.

So just returning should be OK, but just in case that the syntax is OK, but
that a resulting crash_size gets 0, I will add a check like:
     if (!crash_size)
         return;

>> +
>> +	if (crash_base == 0) {
>> +		crash_base = memblock_alloc(crash_size, 1 << 21);
>
> What is this magic number? How about SZ_2M and a comment mentioning the
> arm64 boot protocol?

Right. I will do so.

>> +		if (crash_base == 0) {
>> +			pr_warn("Unable to allocate crashkernel (size:%llx)\n",
>> +				crash_size);
>> +			return;
>> +		}
>> +	} else {
>> +		/* User specifies base address explicitly. */
>> +		if (!memblock_is_region_memory(crash_base, crash_size) ||
>> +			memblock_is_region_reserved(crash_base, crash_size)) {
>> +			pr_warn("crashkernel has wrong address or size\n");
>> +			return;
>> +		}
>> +
>> +		if (crash_base & ((1 << 21) - 1)) {
>
> IS_ALIGNED

OK.

>> +			pr_warn("crashkernel base address is not 2MB aligned\n");
>> +			return;
>> +		}
>> +
>> +		memblock_reserve(crash_base, crash_size);
>> +	}
>> +
>> +	pr_info("Reserving %lldMB of memory at %lldMB for crashkernel\n",
>> +		crash_size >> 20, crash_base >> 20);
>> +
>> +	crashk_res.start = crash_base;
>> +	crashk_res.end = crash_base + crash_size - 1;
>> +}
>
> #else
>
> static void __init reserve_crashkernel(void) {};

OK.

Thanks,
-Takahiro AKASHI

> Will