x86/mm: Skip the hypervisor range when walking PGD

The range between 0xffff800000000000 and 0xffff87ffffffffff is reserved
for hypervisor and therefore we should not try to follow PGD's indexes
corresponding to those addresses.

While this has always been a problem, with the new W+X warning
mechanism ptdump_walk_pgd_level_core() can now be called during boot,
causing a PV Xen guest to crash.

[ tglx: Replaced the macro with a readable inline ]

Fixes: e1a58320a38d "x86/mm: Warn on W^X mappings"
Reported-by: Sander Eikelenboom <linux@eikelenboom.it>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: xen-devel@lists.xen.org
Link: http://lkml.kernel.org/r/1446749795-27764-1-git-send-email-boris.ostrovsky@oracle.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/mm/dump_pagetables.c

@@ -358,6 +358,21 @@ static void walk_pud_level(struct seq_file *m, struct pg_state *st, pgd_t addr,
 #define pgd_none(a)  pud_none(__pud(pgd_val(a)))
 #endif
 
+#ifdef CONFIG_X86_64
+static inline bool is_hypervisor_range(int idx)
+{
+	/*
+	 * ffff800000000000 - ffff87ffffffffff is reserved for
+	 * the hypervisor.
+	 */
+	return paravirt_enabled() &&
+		(idx >= pgd_index(__PAGE_OFFSET) - 16) &&
+		(idx < pgd_index(__PAGE_OFFSET));
+}
+#else
+static inline bool is_hypervisor_range(int idx) { return false; }
+#endif
+
 static void ptdump_walk_pgd_level_core(struct seq_file *m, pgd_t *pgd,
 				       bool checkwx)
 {
@@ -381,7 +396,7 @@ static void ptdump_walk_pgd_level_core(struct seq_file *m, pgd_t *pgd,
 
 	for (i = 0; i < PTRS_PER_PGD; i++) {
 		st.current_address = normalize_addr(i * PGD_LEVEL_MULT);
-		if (!pgd_none(*start)) {
+		if (!pgd_none(*start) && !is_hypervisor_range(i)) {
 			if (pgd_large(*start) || !pgd_present(*start)) {
 				prot = pgd_flags(*start);
 				note_page(m, &st, __pgprot(prot), 1);