Hi Takahiro,

On Thu, 2015-03-26 at 17:28 +0900, AKASHI Takahiro wrote:

On system kernel, the memory region used by crash dump kernel must be
specified by "crashkernel=X at Y" boot parameter. reserve_crashkernel()
will allocate the region in "System RAM" and reserve it for later use.

On crash dump kernel, memory region information in system kernel is
described in a specific region specified by "elfcorehdr=X at Y" boot parameter.
reserve_elfcorehdr() will set aside the region to avoid data destruction
by the kernel.

Crash dump kernel will access memory regions in system kernel via
copy_oldmem_page(), which reads a page with ioremap'ing it assuming that

s/page with/page by/

such pages are not part of main memory of crash dump kernel.
This is true under non-UEFI environment because kexec-tools modifies
a device tree adding "usablemem" attributes to memory sections.
Under UEFI, however, this is not true because UEFI remove memory sections
in a device tree and export all the memory regions, even though they belong
to system kernel.

So we should add "mem=X[MG]" boot parameter to limit the meory size and

s/meory/memory/

I would recommend against adding paths in source files.  It often
happens that files with paths are moved, but the file comments are not
updated.

+ *
+ * Copyright (C) 2014 Linaro Limited
+ * Author: AKASHI Takahiro [off-list ref]
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/crash_dump.h>
+#include <linux/errno.h>
+#include <linux/io.h>
+#include <linux/memblock.h>
+#include <linux/uaccess.h>
+#include <asm/memory.h>
+
+/**
+ * copy_oldmem_page() - copy one page from old kernel memory
+ * @pfn: page frame number to be copied
+ * @buf: buffer where the copied page is placed
+ * @csize: number of bytes to copy
+ * @offset: offset in bytes into the page
+ * @userbuf: if set, @buf is int he user address space

s/is int he user/is a user/

+ *
+ * This function copies one page from old kernel memory into buffer pointed by
+ * @buf. If @buf is in userspace, set @userbuf to %1. Returns number of bytes
+ * copied or negative error in case of failure.
+ */
+ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
+			 size_t csize, unsigned long offset,
+			 int userbuf)

Since userbuf is a binary flag, I think type bool would be better.
Change the comments from 'set' and '1' to 'true'.

Should offset be type size_t?

+{
+	void *vaddr;
+
+	if (!csize)
+		return 0;
+
+	vaddr = ioremap(pfn << PAGE_SHIFT, PAGE_SIZE);
+	if (!vaddr)
+		return -ENOMEM;
+
+	if (userbuf) {
+		if (copy_to_user(buf, vaddr + offset, csize)) {
+			iounmap(vaddr);
+			return -EFAULT;
+		}
+	} else {
+		memcpy(buf, vaddr + offset, csize);
+	}
+
+	iounmap(vaddr);
+
+	return csize;
+}
+
+/**
+ * elfcorehdr_read - read from ELF core header
+ * @buf: buffer where the data is placed
+ * @csize: number of bytes to read
+ * @ppos: address in the memory
+ *
+ * This function reads @count bytes from elf core header which exists
+ * on crash dump kernel's memory.
+ */
+ssize_t elfcorehdr_read(char *buf, size_t count, u64 *ppos)

Should ppos be type phys_addr_t *?

Can we use 0x%llx here and below and avoid these casts?

Maybe have a blank line here?

+	/*
+	 * reserve_crashkernel() and reserver_elfcorehdr() must be called

s/reserver_elfcorehdr/reserve_elfcorehdr/

+	 * before arm64_bootmem_init() because dma_contiguous_reserve()
+	 * may conflict with those regions.
+	 */
+#ifdef CONFIG_KEXEC
+	reserve_crashkernel();
+#endif
+#ifdef CONFIG_CRASH_DUMP
+	reserve_elfcorehdr();
+#endif
 	arm64_memblock_init();
 
 	paging_init();
 	request_standard_resources();
+#ifdef CONFIG_KEXEC
+	/* kexec-tool will detect the region with /proc/iomem */

There are more kexec user programs than kexec-tools, so I think
something like 'user space tools' would be better.

+	insert_resource(&iomem_resource, &crashk_res);
+#endif
 
 	early_ioremap_reset();