x86, kdump: Change copy_oldmem_page() to use cached addressing

The copy of /proc/vmcore to a user buffer proceeds much faster
if the kernel addresses memory as cached.

With this patch we have seen an increase in transfer rate from
less than 15MB/s to 80-460MB/s, depending on size of the
transfer. This makes a big difference in time needed to save a
system dump.
Signed-off-by: NCliff Wickman <cpw@sgi.com>
Acked-by: N"Eric W. Biederman" <ebiederm@xmission.com>
Cc: kexec@lists.infradead.org
Cc: <stable@kernel.org> # as far back as it would apply
LKML-Reference: <E1OtMLz-0001yp-Ia@eag09.americas.sgi.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

arch/x86/kernel/crash_dump_64.c

@@ -34,7 +34,7 @@ ssize_t copy_oldmem_page(unsigned long pfn, char *buf,
 	if (!csize)
 		return 0;
 
-	vaddr = ioremap(pfn << PAGE_SHIFT, PAGE_SIZE);
+	vaddr = ioremap_cache(pfn << PAGE_SHIFT, PAGE_SIZE);
 	if (!vaddr)
 		return -ENOMEM;