arm64: Add HAVE_IOREMAP_PROT support

With ioremap_prot() definition from generic ioremap, also move
pte_pgprot() from hugetlbpage.c into pgtable.h, then arm64 could
have HAVE_IOREMAP_PROT, which will enable generic_access_phys()
code, it is useful for debug, eg, gdb.

Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Link: https://lore.kernel.org/r/20220607125027.44946-7-wangkefeng.wang@huawei.com
Signed-off-by: Will Deacon <will@kernel.org>

Documentation/features/vm/ioremap_prot/arch-support.txt

@@ -9,7 +9,7 @@
     |       alpha: | TODO |
     |         arc: |  ok  |
     |         arm: | TODO |
-    |       arm64: | TODO |
+    |       arm64: |  ok  |
     |        csky: | TODO |
     |     hexagon: | TODO |
     |        ia64: | TODO |

arch/arm64/Kconfig

@@ -189,6 +189,7 @@ config ARM64
 	select HAVE_FUNCTION_GRAPH_TRACER
 	select HAVE_GCC_PLUGINS
 	select HAVE_HW_BREAKPOINT if PERF_EVENTS
+	select HAVE_IOREMAP_PROT
 	select HAVE_IRQ_TIME_ACCOUNTING
 	select HAVE_KVM
 	select HAVE_NMI

arch/arm64/include/asm/pgtable.h

@@ -427,6 +427,16 @@ static inline pte_t pte_swp_clear_exclusive(pte_t pte)
 	return clear_pte_bit(pte, __pgprot(PTE_SWP_EXCLUSIVE));
 }
 
+/*
+ * Select all bits except the pfn
+ */
+static inline pgprot_t pte_pgprot(pte_t pte)
+{
+	unsigned long pfn = pte_pfn(pte);
+
+	return __pgprot(pte_val(pfn_pte(pfn, __pgprot(0))) ^ pte_val(pte));
+}
+
 #ifdef CONFIG_NUMA_BALANCING
 /*
  * See the comment in include/linux/pgtable.h

arch/arm64/mm/hugetlbpage.c

@@ -100,16 +100,6 @@ int pud_huge(pud_t pud)
 #endif
 }
 
-/*
- * Select all bits except the pfn
- */
-static inline pgprot_t pte_pgprot(pte_t pte)
-{
-	unsigned long pfn = pte_pfn(pte);
-
-	return __pgprot(pte_val(pfn_pte(pfn, __pgprot(0))) ^ pte_val(pte));
-}
-
 static int find_num_contig(struct mm_struct *mm, unsigned long addr,
 			   pte_t *ptep, size_t *pgsize)
 {