mm: pgtable: Make generic pgprot_* macros available for no-MMU

The <linux/pgtable.h> header defines some generic pgprot_*
implementations, but they are only available when CONFIG_MMU is enabled.
The RISC-V architecture, for example, therefore defines some of these
pgprot_* macros for !NOMMU.

Let's make the pgprot_* generic available even for !NOMMU so we can
remove the RISC-V specific definitions.

Compile-tested with x86 defconfig, and riscv defconfig and !MMU defconfig.

Suggested-by: Palmer Dabbelt <palmerdabbelt@google.com>
Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

Author: penberg

include/linux/pgtable.h

@@ -647,40 +647,6 @@ static inline int arch_unmap_one(struct mm_struct *mm,
 #define flush_tlb_fix_spurious_fault(vma, address) flush_tlb_page(vma, address)
 #endif
 
-#ifndef pgprot_nx
-#define pgprot_nx(prot)	(prot)
-#endif
-
-#ifndef pgprot_noncached
-#define pgprot_noncached(prot)	(prot)
-#endif
-
-#ifndef pgprot_writecombine
-#define pgprot_writecombine pgprot_noncached
-#endif
-
-#ifndef pgprot_writethrough
-#define pgprot_writethrough pgprot_noncached
-#endif
-
-#ifndef pgprot_device
-#define pgprot_device pgprot_noncached
-#endif
-
-#ifndef pgprot_modify
-#define pgprot_modify pgprot_modify
-static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
-{
-	if (pgprot_val(oldprot) == pgprot_val(pgprot_noncached(oldprot)))
-		newprot = pgprot_noncached(newprot);
-	if (pgprot_val(oldprot) == pgprot_val(pgprot_writecombine(oldprot)))
-		newprot = pgprot_writecombine(newprot);
-	if (pgprot_val(oldprot) == pgprot_val(pgprot_device(oldprot)))
-		newprot = pgprot_device(newprot);
-	return newprot;
-}
-#endif
-
 /*
  * When walking page tables, get the address of the next boundary,
  * or the end address of the range if that comes earlier.  Although no
@@ -840,6 +806,43 @@ static inline void ptep_modify_prot_commit(struct vm_area_struct *vma,
  * No-op macros that just return the current protection value. Defined here
  * because these macros can be used used even if CONFIG_MMU is not defined.
  */
+
+#ifndef pgprot_nx
+#define pgprot_nx(prot)	(prot)
+#endif
+
+#ifndef pgprot_noncached
+#define pgprot_noncached(prot)	(prot)
+#endif
+
+#ifndef pgprot_writecombine
+#define pgprot_writecombine pgprot_noncached
+#endif
+
+#ifndef pgprot_writethrough
+#define pgprot_writethrough pgprot_noncached
+#endif
+
+#ifndef pgprot_device
+#define pgprot_device pgprot_noncached
+#endif
+
+#ifdef CONFIG_MMU
+#ifndef pgprot_modify
+#define pgprot_modify pgprot_modify
+static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
+{
+	if (pgprot_val(oldprot) == pgprot_val(pgprot_noncached(oldprot)))
+		newprot = pgprot_noncached(newprot);
+	if (pgprot_val(oldprot) == pgprot_val(pgprot_writecombine(oldprot)))
+		newprot = pgprot_writecombine(newprot);
+	if (pgprot_val(oldprot) == pgprot_val(pgprot_device(oldprot)))
+		newprot = pgprot_device(newprot);
+	return newprot;
+}
+#endif
+#endif /* CONFIG_MMU */
+
 #ifndef pgprot_encrypted
 #define pgprot_encrypted(prot)	(prot)
 #endif