x86, kexec, 64bit: Only set ident mapping for ram.

We should set mappings only for usable memory ranges under max_pfn
Otherwise causes same problem that is fixed by

x86, mm: Only direct map addresses that are marked as E820_RAM

This patch exposes pfn_mapped array, and only sets ident mapping for ranges
in that array.

This patch relies on new kernel_ident_mapping_init that could handle existing
pgd/pud between different calls.

Signed-off-by: Yinghai Lu <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Cc: Alexander Duyck <[e-mail]>
Signed-off-by: H. Peter Anvin <[e-mail]>

arch/x86/include/asm/page.h

···
 
 struct page;
 
+#include <linux/range.h>
+extern struct range pfn_mapped[];
+extern int nr_pfn_mapped;
+
 static inline void clear_user_page(void *page, unsigned long vaddr,
 				   struct page *pg)
 {

arch/x86/kernel/machine_kexec_64.c

···
 
 	level4p = (pgd_t *)__va(start_pgtable);
 	clear_page(level4p);
-	result = kernel_ident_mapping_init(&info, level4p,
-						0, max_pfn << PAGE_SHIFT);
-	if (result)
-		return result;
+	for (i = 0; i < nr_pfn_mapped; i++) {
+		mstart = pfn_mapped[i].start << PAGE_SHIFT;
+		mend   = pfn_mapped[i].end << PAGE_SHIFT;
+
+		result = kernel_ident_mapping_init(&info,
+						 level4p, mstart, mend);
+		if (result)
+			return result;
+	}
 
 	/*
 	 * segments's mem ranges could be outside 0 ~ max_pfn,

arch/x86/mm/init.c

···
 	return nr_range;
 }
 
-static struct range pfn_mapped[E820_X_MAX];
-static int nr_pfn_mapped;
+struct range pfn_mapped[E820_X_MAX];
+int nr_pfn_mapped;
 
 static void add_pfn_range_mapped(unsigned long start_pfn, unsigned long end_pfn)
 {