arm64: Do not synchronise I and D caches for special ptes

commit 71fdb6bf upstream.

Special pte mappings are not intended to be executable and do not even
have an associated struct page. This patch ensures that we do not call
__sync_icache_dcache() on such ptes.
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Reported-by: Steve Capper <Steve.Capper@arm.com>
Tested-by: Laura Abbott <lauraa@codeaurora.org>
Tested-by: Bharat Bhushan <Bharat.Bhushan@freescale.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

arch/arm64/include/asm/pgtable.h

@@ -168,7 +168,7 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
 			      pte_t *ptep, pte_t pte)
 {
 	if (pte_valid_user(pte)) {
-		if (pte_exec(pte))
+		if (!pte_special(pte) && pte_exec(pte))
 			__sync_icache_dcache(pte, addr);
 		if (!pte_dirty(pte))
 			pte = pte_wrprotect(pte);