powerpc/64s: Use htab_convert_pte_flags() in hash__mark_rodata_ro()

In hash__mark_rodata_ro() we pass the raw PP_RXXX value to
hash__change_memory_range(). That has the effect of setting the key to
zero, because PP_RXXX contains no key value.

Fix it by using htab_convert_pte_flags(), which knows how to convert a
pgprot into a pp value, including the key.

Fixes: d94b827e ("powerpc/book3s64/kuap: Use Key 3 for kernel mapping with hash translation")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Daniel Axtens <dja@axtens.net>
Link: https://lore.kernel.org/r/20210331003845.216246-3-mpe@ellerman.id.au

arch/powerpc/mm/book3s64/hash_pgtable.c

@@ -428,12 +428,14 @@ static bool hash__change_memory_range(unsigned long start, unsigned long end,
 
 void hash__mark_rodata_ro(void)
 {
-	unsigned long start, end;
+	unsigned long start, end, pp;
 
 	start = (unsigned long)_stext;
 	end = (unsigned long)__init_begin;
 
-	WARN_ON(!hash__change_memory_range(start, end, PP_RXXX));
+	pp = htab_convert_pte_flags(pgprot_val(PAGE_KERNEL_ROX), HPTE_USE_KERNEL_KEY);
+
+	WARN_ON(!hash__change_memory_range(start, end, pp));
 }
 
 void hash__mark_initmem_nx(void)