[PATCH] powerpc: Fix /dev/oldmem for kdump

[Sachin P. Sant]

This one has been pending for a long time. Somehow never
made it upstream.

Resending the patch which fixes /dev/oldmem interface for kdump.

Tested with 2.6.26-rc8.

Signed-off-by : Michael Ellerman <[EMAIL PROTECTED]>


Fix /dev/oldmem for kdump

A change to __ioremap() broke reading /dev/oldmem because we're no
longer able to ioremap pfn 0 (d177c207ba16b1db31283e2d1fee7ad4a863584b).

We actually don't need to ioremap for anything that's part of the linear
mapping, so just read it directly.

Also make sure we're only reading one page or less at a time.

Signed-off-by : Michael Ellerman <[EMAIL PROTECTED]>
---

diff -Naurp old/arch/powerpc/kernel/crash_dump.c 
new/arch/powerpc/kernel/crash_dump.c
--- old/arch/powerpc/kernel/crash_dump.c        2008-06-25 07:28:20.000000000 
+0530
+++ new/arch/powerpc/kernel/crash_dump.c        2008-06-26 14:46:17.000000000 
+0530
@@ -83,6 +83,19 @@ static int __init parse_savemaxmem(char 
 }
 __setup("savemaxmem=", parse_savemaxmem);
 
+
+static size_t copy_oldmem_vaddr(void *vaddr, char *buf, size_t csize,
+                               unsigned long offset, int userbuf)
+{
+       if (userbuf) {
+               if (copy_to_user((char __user *)buf, (vaddr + offset), csize))
+                       return -EFAULT;
+       } else
+               memcpy(buf, (vaddr + offset), csize);
+
+       return csize;
+}
+
 /**
  * copy_oldmem_page - copy one page from "oldmem"
  * @pfn: page frame number to be copied
@@ -104,16 +117,16 @@ ssize_t copy_oldmem_page(unsigned long p
        if (!csize)
                return 0;
 
-       vaddr = __ioremap(pfn << PAGE_SHIFT, PAGE_SIZE, 0);
+       csize = min(csize, PAGE_SIZE);
 
-       if (userbuf) {
-               if (copy_to_user((char __user *)buf, (vaddr + offset), csize)) {
-                       iounmap(vaddr);
-                       return -EFAULT;
-               }
-       } else
-               memcpy(buf, (vaddr + offset), csize);
+       if (pfn < max_pfn) {
+               vaddr = __va(pfn << PAGE_SHIFT);
+               csize = copy_oldmem_vaddr(vaddr, buf, csize, offset, userbuf);
+       } else {
+               vaddr = __ioremap(pfn << PAGE_SHIFT, PAGE_SIZE, 0);
+               csize = copy_oldmem_vaddr(vaddr, buf, csize, offset, userbuf);
+               iounmap(vaddr);
+       }
 
-       iounmap(vaddr);
        return csize;
 }

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