arm64: hibernate: add trans_pgd public functions

trans_pgd_create_copy() and trans_pgd_map_page() are going to be
the basis for new shared code that handles page tables for cases
which are between kernels: kexec, and hibernate.

Note: Eventually, get_safe_page() will be moved into a function pointer
passed via argument, but for now keep it as is.

Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: James Morse <james.morse@arm.com>
[will: Keep these functions static until kexec needs them]
Signed-off-by: Will Deacon <will@kernel.org>

arch/arm64/kernel/hibernate.c

@@ -182,39 +182,15 @@ int arch_hibernation_header_restore(void *addr)
 }
 EXPORT_SYMBOL(arch_hibernation_header_restore);
 
-/*
+static int trans_pgd_map_page(pgd_t *trans_pgd, void *page,
- * Copies length bytes, starting at src_start into an new page,
+		       unsigned long dst_addr,
- * perform cache maintentance, then maps it at the specified address low
+		       pgprot_t pgprot)
- * address as executable.
- *
- * This is used by hibernate to copy the code it needs to execute when
- * overwriting the kernel text. This function generates a new set of page
- * tables, which it loads into ttbr0.
- *
- * Length is provided as we probably only want 4K of data, even on a 64K
- * page system.
- */
-static int create_safe_exec_page(void *src_start, size_t length,
-				 unsigned long dst_addr,
-				 phys_addr_t *phys_dst_addr)
 {
-	void *page = (void *)get_safe_page(GFP_ATOMIC);
-	pgd_t *trans_pgd;
 	pgd_t *pgdp;
 	pud_t *pudp;
 	pmd_t *pmdp;
 	pte_t *ptep;
 
-	if (!page)
-		return -ENOMEM;
-
-	memcpy(page, src_start, length);
-	__flush_icache_range((unsigned long)page, (unsigned long)page + length);
-
-	trans_pgd = (void *)get_safe_page(GFP_ATOMIC);
-	if (!trans_pgd)
-		return -ENOMEM;
-
 	pgdp = pgd_offset_raw(trans_pgd, dst_addr);
 	if (pgd_none(READ_ONCE(*pgdp))) {
 		pudp = (void *)get_safe_page(GFP_ATOMIC);
@@ -242,6 +218,44 @@ static int create_safe_exec_page(void *src_start, size_t length,
 	ptep = pte_offset_kernel(pmdp, dst_addr);
 	set_pte(ptep, pfn_pte(virt_to_pfn(page), PAGE_KERNEL_EXEC));
 
+	return 0;
+}
+
+/*
+ * Copies length bytes, starting at src_start into an new page,
+ * perform cache maintenance, then maps it at the specified address low
+ * address as executable.
+ *
+ * This is used by hibernate to copy the code it needs to execute when
+ * overwriting the kernel text. This function generates a new set of page
+ * tables, which it loads into ttbr0.
+ *
+ * Length is provided as we probably only want 4K of data, even on a 64K
+ * page system.
+ */
+static int create_safe_exec_page(void *src_start, size_t length,
+				 unsigned long dst_addr,
+				 phys_addr_t *phys_dst_addr)
+{
+	void *page = (void *)get_safe_page(GFP_ATOMIC);
+	pgd_t *trans_pgd;
+	int rc;
+
+	if (!page)
+		return -ENOMEM;
+
+	memcpy(page, src_start, length);
+	__flush_icache_range((unsigned long)page, (unsigned long)page + length);
+
+	trans_pgd = (void *)get_safe_page(GFP_ATOMIC);
+	if (!trans_pgd)
+		return -ENOMEM;
+
+	rc = trans_pgd_map_page(trans_pgd, page, dst_addr,
+				PAGE_KERNEL_EXEC);
+	if (rc)
+		return rc;
+
 	/*
 	 * Load our new page tables. A strict BBM approach requires that we
 	 * ensure that TLBs are free of any entries that may overlap with the
@@ -462,6 +476,24 @@ static int copy_page_tables(pgd_t *dst_pgdp, unsigned long start,
 	return 0;
 }
 
+static int trans_pgd_create_copy(pgd_t **dst_pgdp, unsigned long start,
+			  unsigned long end)
+{
+	int rc;
+	pgd_t *trans_pgd = (pgd_t *)get_safe_page(GFP_ATOMIC);
+
+	if (!trans_pgd) {
+		pr_err("Failed to allocate memory for temporary page tables.\n");
+		return -ENOMEM;
+	}
+
+	rc = copy_page_tables(trans_pgd, start, end);
+	if (!rc)
+		*dst_pgdp = trans_pgd;
+
+	return rc;
+}
+
 /*
  * Setup then Resume from the hibernate image using swsusp_arch_suspend_exit().
  *
@@ -483,12 +515,7 @@ int swsusp_arch_resume(void)
 	 * Create a second copy of just the linear map, and use this when
 	 * restoring.
 	 */
-	tmp_pg_dir = (pgd_t *)get_safe_page(GFP_ATOMIC);
+	rc = trans_pgd_create_copy(&tmp_pg_dir, PAGE_OFFSET, PAGE_END);
-	if (!tmp_pg_dir) {
-		pr_err("Failed to allocate memory for temporary page tables.\n");
-		return -ENOMEM;
-	}
-	rc = copy_page_tables(tmp_pg_dir, PAGE_OFFSET, PAGE_END);
 	if (rc)
 		return rc;