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

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 <[e-mail]>
Reported-by: Steve Capper <[e-mail]>
Tested-by: Laura Abbott <[e-mail]>
Tested-by: Bharat Bhushan <[e-mail]>
Cc: <[e-mail]>

arch/arm64/include/asm/pgtable.h

···
 			      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_write(pte))
 			pte_val(pte) &= ~PTE_RDONLY;