powerpc: Fix /dev/oldmem interface for kdump

A change to __ioremap() broke reading /dev/oldmem because we're no
longer able to ioremap pfn 0 (d177c207, "[PATCH] powerpc: IOMMU: don't
ioremap null addresses").

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 <michael@ellerman.id.au>
Signed-off-by: Sachin Sant <sachinp@in.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

diff --git a/arch/powerpc/kernel/crash_dump.c b/arch/powerpc/kernel/crash_dump.c
index e0debcca0bfadaf03dbc6f3c35a56f1ad4a3aee2..a323c9b32ee12f76604631a532e2c5dc85436aa1 100644 (file)
--- a/arch/powerpc/kernel/crash_dump.c
+++ b/arch/powerpc/kernel/crash_dump.c
@@ -86,6 +86,19 @@ static int __init parse_savemaxmem(char *p)
 }
 __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
@@ -107,16 +120,16 @@ ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
        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;
 }