[PATCH] kdump: read previous kernel's memory

- Moving the crash_dump.c file to arch dependent part as kmap_atomic_pfn is
  specific to i386 and highmem may not exist in other archs.

- Use ioremap for x86_64 to map the previous kernel memory.

- In copy_oldmem_page(), we now directly copy to the user/kernel buffer and
  avoid the unneccesary copy to a kmalloc'd page.

Signed-off-by: Rachita Kothiyal <rachita@in.ibm.com>
Signed-off-by: Vivek Goyal <vgoyal@in.ibm.com>
Cc: Andi Kleen <ak@muc.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 74 insertions, 0 deletions

diff --git a/arch/i386/kernel/crash_dump.c b/arch/i386/kernel/crash_dump.c
new file mode 100644
index 00000000000..3f532df488b
--- /dev/null
+++ b/arch/i386/kernel/crash_dump.c
@@ -0,0 +1,74 @@
+/*
+ *      kernel/crash_dump.c - Memory preserving reboot related code.
+ *
+ *      Created by: Hariprasad Nellitheertha (hari@in.ibm.com)
+ *      Copyright (C) IBM Corporation, 2004. All rights reserved
+ */
+
+#include <linux/errno.h>
+#include <linux/highmem.h>
+#include <linux/crash_dump.h>
+
+#include <asm/uaccess.h>
+
+static void *kdump_buf_page;
+
+/**
+ * copy_oldmem_page - copy one page from "oldmem"
+ * @pfn: page frame number to be copied
+ * @buf: target memory address for the copy; this can be in kernel address
+ *      space or user address space (see @userbuf)
+ * @csize: number of bytes to copy
+ * @offset: offset in bytes into the page (based on pfn) to begin the copy
+ * @userbuf: if set, @buf is in user address space, use copy_to_user(),
+ *      otherwise @buf is in kernel address space, use memcpy().
+ *
+ * Copy a page from "oldmem". For this page, there is no pte mapped
+ * in the current kernel. We stitch up a pte, similar to kmap_atomic.
+ *
+ * Calling copy_to_user() in atomic context is not desirable. Hence first
+ * copying the data to a pre-allocated kernel page and then copying to user
+ * space in non-atomic context.
+ */
+ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
+                               size_t csize, unsigned long offset, int userbuf)
+{
+        void  *vaddr;
+
+        if (!csize)
+                return 0;
+
+        vaddr = kmap_atomic_pfn(pfn, KM_PTE0);
+
+        if (!userbuf) {
+                memcpy(buf, (vaddr + offset), csize);
+                kunmap_atomic(vaddr, KM_PTE0);
+        } else {
+                if (!kdump_buf_page) {
+                        printk(KERN_WARNING "Kdump: Kdump buffer page not"
+                                " allocated\n");
+                        return -EFAULT;
+                }
+                copy_page(kdump_buf_page, vaddr);
+                kunmap_atomic(vaddr, KM_PTE0);
+                if (copy_to_user(buf, (kdump_buf_page + offset), csize))
+                        return -EFAULT;
+        }
+
+        return csize;
+}
+
+static int __init kdump_buf_page_init(void)
+{
+        int ret = 0;
+
+        kdump_buf_page = kmalloc(PAGE_SIZE, GFP_KERNEL);
+        if (!kdump_buf_page) {
+                printk(KERN_WARNING "Kdump: Failed to allocate kdump buffer"
+                         " page\n");
+                ret = -ENOMEM;
+        }
+
+        return ret;
+}
+arch_initcall(kdump_buf_page_init);