powerpc/8xx: Fix pte_access_permitted() for PAGE_NONE

On 8xx, PAGE_NONE is handled by setting _PAGE_NA instead of clearing
_PAGE_USER.

But then pte_user() returns 1 also for PAGE_NONE.

As _PAGE_NA prevent reads, add a specific version of pte_read()
that returns 0 when _PAGE_NA is set instead of always returning 1.

Fixes: 35175033 ("powerpc/mm: Introduce _PAGE_NA")
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/57bcfbe578e43123f9ed73e040229b80f1ad56ec.1695659959.git.christophe.leroy@csgroup.eu

arch/powerpc/include/asm/nohash/32/pte-8xx.h

@@ -94,6 +94,13 @@ static inline pte_t pte_wrprotect(pte_t pte)
 
 #define pte_wrprotect pte_wrprotect
 
+static inline int pte_read(pte_t pte)
+{
+	return (pte_val(pte) & _PAGE_RO) != _PAGE_NA;
+}
+
+#define pte_read pte_read
+
 static inline int pte_write(pte_t pte)
 {
 	return !(pte_val(pte) & _PAGE_RO);

arch/powerpc/include/asm/nohash/pgtable.h

@@ -25,7 +25,9 @@ static inline int pte_write(pte_t pte)
 	return pte_val(pte) & _PAGE_RW;
 }
 #endif
+#ifndef pte_read
 static inline int pte_read(pte_t pte)		{ return 1; }
+#endif
 static inline int pte_dirty(pte_t pte)		{ return pte_val(pte) & _PAGE_DIRTY; }
 static inline int pte_special(pte_t pte)	{ return pte_val(pte) & _PAGE_SPECIAL; }
 static inline int pte_none(pte_t pte)		{ return (pte_val(pte) & ~_PTE_NONE_MASK) == 0; }