arm64: use fixmap region for permanent FDT mapping

Currently, the FDT blob needs to be in the same 512 MB region as
the kernel, so that it can be mapped into the kernel virtual memory
space very early on using a minimal set of statically allocated
translation tables.

Now that we have early fixmap support, we can relax this restriction,
by moving the permanent FDT mapping to the fixmap region instead.
This way, the FDT blob may be anywhere in memory.

This also moves the vetting of the FDT to mmu.c, since the early
init code in head.S does not handle mapping of the FDT anymore.
At the same time, fix up some comments in head.S that have gone stale.

Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

2 files changed, 11 insertions, 58 deletions

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 19f915e8f6e0..30cffc5e7402 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -237,8 +237,6 @@ ENTRY(stext)
 	bl	el2_setup			// Drop to EL1, w20=cpu_boot_mode
 	adrp	x24, __PHYS_OFFSET
 	bl	set_cpu_boot_mode_flag
-
-	bl	__vet_fdt
 	bl	__create_page_tables		// x25=TTBR0, x26=TTBR1
 	/*
 	 * The following calls CPU setup code, see arch/arm64/mm/proc.S for
@@ -270,24 +268,6 @@ preserve_boot_args:
 ENDPROC(preserve_boot_args)
 
 /*
- * Determine validity of the x21 FDT pointer.
- * The dtb must be 8-byte aligned and live in the first 512M of memory.
- */
-__vet_fdt:
-	tst	x21, #0x7
-	b.ne	1f
-	cmp	x21, x24
-	b.lt	1f
-	mov	x0, #(1 << 29)
-	add	x0, x0, x24
-	cmp	x21, x0
-	b.ge	1f
-	ret
-1:
-	mov	x21, #0
-	ret
-ENDPROC(__vet_fdt)
-/*
  * Macro to create a table entry to the next page.
  *
  *	tbl:	page table address
@@ -348,8 +328,7 @@ ENDPROC(__vet_fdt)
  * required to get the kernel running. The following sections are required:
  *   - identity mapping to enable the MMU (low address, TTBR0)
  *   - first few MB of the kernel linear mapping to jump to once the MMU has
- *     been enabled, including the FDT blob (TTBR1)
- *   - pgd entry for fixed mappings (TTBR1)
+ *     been enabled
  */
 __create_page_tables:
 	adrp	x25, idmap_pg_dir
@@ -439,22 +418,6 @@ __create_page_tables:
 	create_block_map x0, x7, x3, x5, x6
 
 	/*
-	 * Map the FDT blob (maximum 2MB; must be within 512MB of
-	 * PHYS_OFFSET).
-	 */
-	mov	x3, x21				// FDT phys address
-	and	x3, x3, #~((1 << 21) - 1)	// 2MB aligned
-	mov	x6, #PAGE_OFFSET
-	sub	x5, x3, x24			// subtract PHYS_OFFSET
-	tst	x5, #~((1 << 29) - 1)		// within 512MB?
-	csel	x21, xzr, x21, ne		// zero the FDT pointer
-	b.ne	1f
-	add	x5, x5, x6			// __va(FDT blob)
-	add	x6, x5, #1 << 21		// 2MB for the FDT blob
-	sub	x6, x6, #1			// inclusive range
-	create_block_map x0, x7, x3, x5, x6
-1:
-	/*
 	 * Since the page tables have been populated with non-cacheable
 	 * accesses (MMU disabled), invalidate the idmap and swapper page
 	 * tables again to remove any speculatively loaded cache lines.
diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
index 508cca1f8dce..ffd3970721bf 100644
--- a/arch/arm64/kernel/setup.c
+++ b/arch/arm64/kernel/setup.c
@@ -105,18 +105,6 @@ static struct resource mem_res[] = {
 #define kernel_code mem_res[0]
 #define kernel_data mem_res[1]
 
-void __init early_print(const char *str, ...)
-{
-	char buf[256];
-	va_list ap;
-
-	va_start(ap, str);
-	vsnprintf(buf, sizeof(buf), str, ap);
-	va_end(ap);
-
-	printk("%s", buf);
-}
-
 /*
  * The recorded values of x0 .. x3 upon kernel entry.
  */
@@ -326,12 +314,14 @@ static void __init setup_processor(void)
 
 static void __init setup_machine_fdt(phys_addr_t dt_phys)
 {
-	if (!dt_phys || !early_init_dt_scan(phys_to_virt(dt_phys))) {
-		early_print("\n"
-			"Error: invalid device tree blob at physical address 0x%p (virtual address 0x%p)\n"
-			"The dtb must be 8-byte aligned and passed in the first 512MB of memory\n"
-			"\nPlease check your bootloader.\n",
-			dt_phys, phys_to_virt(dt_phys));
+	void *dt_virt = fixmap_remap_fdt(dt_phys);
+
+	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"
+			"The dtb must be 8-byte aligned and must not exceed 2 MB in size\n"
+			"\nPlease check your bootloader.",
+			&dt_phys, dt_virt);
 
 		while (true)
 			cpu_relax();
@@ -374,8 +364,6 @@ void __init setup_arch(char **cmdline_p)
 {
 	setup_processor();
 
-	setup_machine_fdt(__fdt_pointer);
-
 	init_mm.start_code = (unsigned long) _text;
 	init_mm.end_code   = (unsigned long) _etext;
 	init_mm.end_data   = (unsigned long) _edata;
@@ -386,6 +374,8 @@ void __init setup_arch(char **cmdline_p)
 	early_fixmap_init();
 	early_ioremap_init();
 
+	setup_machine_fdt(__fdt_pointer);
+
 	parse_early_param();
 
 	/*