arm64: map FDT as RW for early_init_dt_scan()

Currently in arm64, FDT is mapped to RO before it's passed to
early_init_dt_scan(). However, there might be some codes
(eg. commit "fdt: add support for rng-seed") that need to modify FDT
during init. Map FDT to RO after early fixups are done.

Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Will Deacon <will@kernel.org>

arch/arm64/include/asm/mmu.h

@@ -126,7 +126,7 @@ extern void init_mem_pgprot(void);
 extern void create_pgd_mapping(struct mm_struct *mm, phys_addr_t phys,
 			       unsigned long virt, phys_addr_t size,
 			       pgprot_t prot, bool page_mappings_only);
-extern void *fixmap_remap_fdt(phys_addr_t dt_phys);
+extern void *fixmap_remap_fdt(phys_addr_t dt_phys, int *size, pgprot_t prot);
 extern void mark_linear_text_alias_ro(void);
 
 #define INIT_MM_CONTEXT(name)	\

arch/arm64/kernel/kaslr.c

@@ -62,9 +62,6 @@ static __init const u8 *kaslr_get_cmdline(void *fdt)
 	return default_cmdline;
 }
 
-extern void *__init __fixmap_remap_fdt(phys_addr_t dt_phys, int *size,
-				       pgprot_t prot);
-
 /*
  * This routine will be executed with the kernel mapped at its default virtual
  * address, and if it returns successfully, the kernel will be remapped, and
@@ -93,7 +90,7 @@ u64 __init kaslr_early_init(u64 dt_phys)
 	 * attempt at mapping the FDT in setup_machine()
 	 */
 	early_fixmap_init();
-	fdt = __fixmap_remap_fdt(dt_phys, &size, PAGE_KERNEL);
+	fdt = fixmap_remap_fdt(dt_phys, &size, PAGE_KERNEL);
 	if (!fdt)
 		return 0;
 

arch/arm64/kernel/setup.c

@@ -170,9 +170,13 @@ static void __init smp_build_mpidr_hash(void)
 
 static void __init setup_machine_fdt(phys_addr_t dt_phys)
 {
-	void *dt_virt = fixmap_remap_fdt(dt_phys);
+	int size;
+	void *dt_virt = fixmap_remap_fdt(dt_phys, &size, PAGE_KERNEL);
 	const char *name;
 
+	if (dt_virt)
+		memblock_reserve(dt_phys, size);
+
 	if (!dt_virt || !early_init_dt_scan(dt_virt)) {
 		pr_crit("\n"
 			"Error: invalid device tree blob at physical address %pa (virtual address 0x%p)\n"
@@ -184,6 +188,9 @@ static void __init setup_machine_fdt(phys_addr_t dt_phys)
 			cpu_relax();
 	}
 
+	/* Early fixups are done, map the FDT as read-only now */
+	fixmap_remap_fdt(dt_phys, &size, PAGE_KERNEL_RO);
+
 	name = of_flat_dt_get_machine_name();
 	if (!name)
 		return;

arch/arm64/mm/mmu.c

@@ -876,7 +876,7 @@ void __set_fixmap(enum fixed_addresses idx,
 	}
 }
 
-void *__init __fixmap_remap_fdt(phys_addr_t dt_phys, int *size, pgprot_t prot)
+void *__init fixmap_remap_fdt(phys_addr_t dt_phys, int *size, pgprot_t prot)
 {
 	const u64 dt_virt_base = __fix_to_virt(FIX_FDT);
 	int offset;
@@ -929,19 +929,6 @@ void *__init __fixmap_remap_fdt(phys_addr_t dt_phys, int *size, pgprot_t prot)
 	return dt_virt;
 }
 
-void *__init fixmap_remap_fdt(phys_addr_t dt_phys)
-{
-	void *dt_virt;
-	int size;
-
-	dt_virt = __fixmap_remap_fdt(dt_phys, &size, PAGE_KERNEL_RO);
-	if (!dt_virt)
-		return NULL;
-
-	memblock_reserve(dt_phys, size);
-	return dt_virt;
-}
-
 int __init arch_ioremap_p4d_supported(void)
 {
 	return 0;