x86, kdump: fix invalid access on i386 sparsemem

Impact: fix kdump crash on 32-bit sparsemem kernels

Since linux-2.6.27, kdump has failed on i386 sparsemem kernel.
1st-kernel gets a panic just before switching to 2nd-kernel.

The cause is that a kernel accesses invalid mem_section by
page_to_pfn(image->swap_page) at machine_kexec().
image->swap_page is allocated if kexec for hibernation, but
it is not allocated if kdump. So if kdump, a kernel should
not access the mem_section corresponding to image->swap_page.

The attached patch fixes this invalid access.
Signed-off-by: Ken'ichi Ohmichi <oomichi@mxs.nes.nec.co.jp>
Cc: kexec-ml <kexec@lists.infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/machine_kexec_32.c

@@ -162,7 +162,10 @@ void machine_kexec(struct kimage *image)
 	page_list[VA_PTE_0] = (unsigned long)kexec_pte0;
 	page_list[PA_PTE_1] = __pa(kexec_pte1);
 	page_list[VA_PTE_1] = (unsigned long)kexec_pte1;
-	page_list[PA_SWAP_PAGE] = (page_to_pfn(image->swap_page) << PAGE_SHIFT);
+
+	if (image->type == KEXEC_TYPE_DEFAULT)
+		page_list[PA_SWAP_PAGE] = (page_to_pfn(image->swap_page)
+						<< PAGE_SHIFT);
 
 	/* The segment registers are funny things, they have both a
 	 * visible and an invisible part.  Whenever the visible part is