Re: [PATCH v2 3/3] arm64: kexec_file: add crash dump support

[Bhupesh Sharma]

On 11/14/2019 10:45 AM, AKASHI Takahiro wrote:
> Enabling crash dump (kdump) includes
> * prepare contents of ELF header of a core dump file, /proc/vmcore,
>    using crash_prepare_elf64_headers(), and
> * add two device tree properties, "linux,usable-memory-range" and
>    "linux,elfcorehdr", which represent respectively a memory range
>    to be used by crash dump kernel and the header's location
>
> Signed-off-by: AKASHI Takahiro <takahiro.akashi@xxxxxxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Will Deacon <will.deacon@xxxxxxx>
> Reviewed-by: James Morse <james.morse@xxxxxxx>
> ---
>   arch/arm64/include/asm/kexec.h         |   4 +
>   arch/arm64/kernel/kexec_image.c        |   4 -
>   arch/arm64/kernel/machine_kexec_file.c | 106 ++++++++++++++++++++++++-
>   3 files changed, 106 insertions(+), 8 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kexec.h b/arch/arm64/include/asm/kexec.h
> index 12a561a54128..d24b527e8c00 100644
> --- a/arch/arm64/include/asm/kexec.h
> +++ b/arch/arm64/include/asm/kexec.h
> @@ -96,6 +96,10 @@ static inline void crash_post_resume(void) {}
>   struct kimage_arch {
>   	void *dtb;
>   	unsigned long dtb_mem;
> +	/* Core ELF header buffer */
> +	void *elf_headers;
> +	unsigned long elf_headers_mem;
> +	unsigned long elf_headers_sz;
>   };
>   
>   extern const struct kexec_file_ops kexec_image_ops;
> diff --git a/arch/arm64/kernel/kexec_image.c b/arch/arm64/kernel/kexec_image.c
> index 29a9428486a5..af9987c154ca 100644
> --- a/arch/arm64/kernel/kexec_image.c
> +++ b/arch/arm64/kernel/kexec_image.c
> @@ -47,10 +47,6 @@ static void *image_load(struct kimage *image,
>   	struct kexec_segment *kernel_segment;
>   	int ret;
>   
> -	/* We don't support crash kernels yet. */
> -	if (image->type == KEXEC_TYPE_CRASH)
> -		return ERR_PTR(-EOPNOTSUPP);
> -
>   	/*
>   	 * We require a kernel with an unambiguous Image header. Per
>   	 * Documentation/arm64/booting.rst, this is the case when image_size
> diff --git a/arch/arm64/kernel/machine_kexec_file.c b/arch/arm64/kernel/machine_kexec_file.c
> index 7b08bf9499b6..f1d1bb895fd2 100644
> --- a/arch/arm64/kernel/machine_kexec_file.c
> +++ b/arch/arm64/kernel/machine_kexec_file.c
> @@ -17,12 +17,15 @@
>   #include <linux/memblock.h>
>   #include <linux/of_fdt.h>
>   #include <linux/random.h>
> +#include <linux/slab.h>
>   #include <linux/string.h>
>   #include <linux/types.h>
>   #include <linux/vmalloc.h>
>   #include <asm/byteorder.h>
>   
>   /* relevant device tree properties */
> +#define FDT_PROP_KEXEC_ELFHDR	"linux,elfcorehdr"
> +#define FDT_PROP_MEM_RANGE	"linux,usable-memory-range"
>   #define FDT_PROP_INITRD_START	"linux,initrd-start"
>   #define FDT_PROP_INITRD_END	"linux,initrd-end"
>   #define FDT_PROP_BOOTARGS	"bootargs"
> @@ -40,6 +43,10 @@ int arch_kimage_file_post_load_cleanup(struct kimage *image)
>   	vfree(image->arch.dtb);
>   	image->arch.dtb = NULL;
>   
> +	vfree(image->arch.elf_headers);
> +	image->arch.elf_headers = NULL;
> +	image->arch.elf_headers_sz = 0;
> +
>   	return kexec_image_post_load_cleanup_default(image);
>   }
>   
> @@ -55,6 +62,31 @@ static int setup_dtb(struct kimage *image,
>   
>   	off = ret;
>   
> +	ret = fdt_delprop(dtb, off, FDT_PROP_KEXEC_ELFHDR);
> +	if (ret && ret != -FDT_ERR_NOTFOUND)
> +		goto out;
> +	ret = fdt_delprop(dtb, off, FDT_PROP_MEM_RANGE);
> +	if (ret && ret != -FDT_ERR_NOTFOUND)
> +		goto out;
> +
> +	if (image->type == KEXEC_TYPE_CRASH) {
> +		/* add linux,elfcorehdr */
> +		ret = fdt_appendprop_addrrange(dtb, 0, off,
> +				FDT_PROP_KEXEC_ELFHDR,
> +				image->arch.elf_headers_mem,
> +				image->arch.elf_headers_sz);
> +		if (ret)
> +			return (ret == -FDT_ERR_NOSPACE ? -ENOMEM : -EINVAL);
> +
> +		/* add linux,usable-memory-range */
> +		ret = fdt_appendprop_addrrange(dtb, 0, off,
> +				FDT_PROP_MEM_RANGE,
> +				crashk_res.start,
> +				crashk_res.end - crashk_res.start + 1);
> +		if (ret)
> +			return (ret == -FDT_ERR_NOSPACE ? -ENOMEM : -EINVAL);
> +	}
> +
>   	/* add bootargs */
>   	if (cmdline) {
>   		ret = fdt_setprop_string(dtb, off, FDT_PROP_BOOTARGS, cmdline);
> @@ -125,8 +157,8 @@ static int setup_dtb(struct kimage *image,
>   }
>   
>   /*
> - * More space needed so that we can add initrd, bootargs, kaslr-seed, and
> - * rng-seed.
> + * More space needed so that we can add initrd, bootargs, kaslr-seed,
> + * rng-seed, userable-memory-range and elfcorehdr.

nitpick:
s/userable-memory-range/usable-memory-range

>    */
>   #define DTB_EXTRA_SPACE 0x1000
>   
> @@ -174,6 +206,43 @@ static int create_dtb(struct kimage *image,
>   	}
>   }
>   
> +static int prepare_elf_headers(void **addr, unsigned long *sz)
> +{
> +	struct crash_mem *cmem;
> +	unsigned int nr_ranges;
> +	int ret;
> +	u64 i;
> +	phys_addr_t start, end;
> +
> +	nr_ranges = 1; /* for exclusion of crashkernel region */
> +	for_each_mem_range(i, &memblock.memory, NULL, NUMA_NO_NODE,
> +					MEMBLOCK_NONE, &start, &end, NULL)
> +		nr_ranges++;
> +
> +	cmem = kmalloc(sizeof(struct crash_mem) +
> +			sizeof(struct crash_mem_range) * nr_ranges, GFP_KERNEL);
> +	if (!cmem)
> +		return -ENOMEM;
> +
> +	cmem->max_nr_ranges = nr_ranges;
> +	cmem->nr_ranges = 0;
> +	for_each_mem_range(i, &memblock.memory, NULL, NUMA_NO_NODE,
> +					MEMBLOCK_NONE, &start, &end, NULL) {
> +		cmem->ranges[cmem->nr_ranges].start = start;
> +		cmem->ranges[cmem->nr_ranges].end = end - 1;
> +		cmem->nr_ranges++;
> +	}
> +
> +	/* Exclude crashkernel region */
> +	ret = crash_exclude_mem_range(cmem, crashk_res.start, crashk_res.end);
> +
> +	if (!ret)
> +		ret =  crash_prepare_elf64_headers(cmem, true, addr, sz);
> +
> +	kfree(cmem);
> +	return ret;
> +}
> +
>   int load_other_segments(struct kimage *image,
>   			unsigned long kernel_load_addr,
>   			unsigned long kernel_size,
> @@ -181,14 +250,43 @@ int load_other_segments(struct kimage *image,
>   			char *cmdline)
>   {
>   	struct kexec_buf kbuf;
> -	void *dtb = NULL;
> -	unsigned long initrd_load_addr = 0, dtb_len;
> +	void *headers, *dtb = NULL;
> +	unsigned long headers_sz, initrd_load_addr = 0, dtb_len;
>   	int ret = 0;
>   
>   	kbuf.image = image;
>   	/* not allocate anything below the kernel */
>   	kbuf.buf_min = kernel_load_addr + kernel_size;
>   
> +	/* load elf core header */
> +	if (image->type == KEXEC_TYPE_CRASH) {
> +		ret = prepare_elf_headers(&headers, &headers_sz);
> +		if (ret) {
> +			pr_err("Preparing elf core header failed\n");
> +			goto out_err;
> +		}
> +
> +		kbuf.buffer = headers;
> +		kbuf.bufsz = headers_sz;
> +		kbuf.mem = 0;

With commit c19d050f8088 ("arm64/kexec: Use consistent convention of 
initializing 'kxec_buf.mem' with KEXEC_BUF_MEM_UNKNOWN"), we are trying 
to standardize the way of setting up initial value of 'kbuf.mem'. So we 
can use the following notion (in v3?) instead:
		kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;

> +		kbuf.memsz = headers_sz;
> +		kbuf.buf_align = SZ_64K; /* largest supported page size */
> +		kbuf.buf_max = ULONG_MAX;
> +		kbuf.top_down = true;
> +
> +		ret = kexec_add_buffer(&kbuf);
> +		if (ret) {
> +			vfree(headers);
> +			goto out_err;
> +		}
> +		image->arch.elf_headers = headers;
> +		image->arch.elf_headers_mem = kbuf.mem;
> +		image->arch.elf_headers_sz = headers_sz;
> +
> +		pr_debug("Loaded elf core header at 0x%lx bufsz=0x%lx memsz=0x%lx\n",
> +			 image->arch.elf_headers_mem, headers_sz, headers_sz);
> +	}
> +
>   	/* load initrd */
>   	if (initrd) {
>   		kbuf.buffer = initrd;

Thanks,
Bhupesh