efi/arm-stub: Round up FDT allocation to mapping size

The FDT is mapped via a fixmap entry that is at least 2 MB in size and
2 MB aligned on 4 KB page size kernels.

On UEFI systems, the FDT allocation may share this 2 MB mapping with a
reserved region (or another memory region that we should never map),
unless we account for this in the size of the allocation (the alignment
is already 2 MB)

So instead of taking guesses at the needed space, simply allocate 2 MB
immediately. The allocation will be recorded as EFI_LOADER_DATA, and the
kernel only memblock_reserve()'s the actual size of the FDT, so the
unused space will be released back to the kernel.
Reviewed-By: Jeffrey Hugo <jhugo@codeaurora.org>
Tested-by: Richard Ruigrok <rruigrok@codeaurora.org>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Link: http://lkml.kernel.org/r/20170404160245.27812-6-ard.biesheuvel@linaro.orgSigned-off-by: Ingo Molnar <mingo@kernel.org>

arch/arm64/include/asm/efi.h

 #ifndef _ASM_EFI_H
 #define _ASM_EFI_H
 
+#include <asm/boot.h>
 #include <asm/cpufeature.h>
 #include <asm/io.h>
 #include <asm/mmu_context.h>

drivers/firmware/efi/libstub/fdt.c

@@ -206,6 +206,10 @@ static efi_status_t exit_boot_func(efi_system_table_t *sys_table_arg,
 	return update_fdt_memmap(p->new_fdt_addr, map);
 }
 
+#ifndef MAX_FDT_SIZE
+#define MAX_FDT_SIZE	SZ_2M
+#endif
+
 /*
  * Allocate memory for a new FDT, then add EFI, commandline, and
  * initrd related fields to the FDT.  This routine increases the
@@ -233,7 +237,6 @@ efi_status_t allocate_new_fdt_and_exit_boot(efi_system_table_t *sys_table,
 	u32 desc_ver;
 	unsigned long mmap_key;
 	efi_memory_desc_t *memory_map, *runtime_map;
-	unsigned long new_fdt_size;
 	efi_status_t status;
 	int runtime_entry_count = 0;
 	struct efi_boot_memmap map;
@@ -262,42 +265,30 @@ efi_status_t allocate_new_fdt_and_exit_boot(efi_system_table_t *sys_table,
 	       "Exiting boot services and installing virtual address map...\n");
 
 	map.map = &memory_map;
-	/*
-	 * Estimate size of new FDT, and allocate memory for it. We
-	 * will allocate a bigger buffer if this ends up being too
-	 * small, so a rough guess is OK here.
-	 */
-	new_fdt_size = fdt_size + EFI_PAGE_SIZE;
-	while (1) {
-		status = efi_high_alloc(sys_table, new_fdt_size, EFI_FDT_ALIGN,
+	status = efi_high_alloc(sys_table, MAX_FDT_SIZE, EFI_FDT_ALIGN,
 				new_fdt_addr, max_addr);
 	if (status != EFI_SUCCESS) {
-			pr_efi_err(sys_table, "Unable to allocate memory for new device tree.\n");
+		pr_efi_err(sys_table,
+			   "Unable to allocate memory for new device tree.\n");
 		goto fail;
 	}
 
-		status = update_fdt(sys_table,
-				    (void *)fdt_addr, fdt_size,
-				    (void *)*new_fdt_addr, new_fdt_size,
-				    cmdline_ptr, initrd_addr, initrd_size);
-
-		/* Succeeding the first time is the expected case. */
-		if (status == EFI_SUCCESS)
-			break;
-
-		if (status == EFI_BUFFER_TOO_SMALL) {
 	/*
-			 * We need to allocate more space for the new
-			 * device tree, so free existing buffer that is
-			 * too small.
+	 * Now that we have done our final memory allocation (and free)
+	 * we can get the memory map key needed for exit_boot_services().
 	 */
-			efi_free(sys_table, new_fdt_size, *new_fdt_addr);
-			new_fdt_size += EFI_PAGE_SIZE;
-		} else {
+	status = efi_get_memory_map(sys_table, &map);
+	if (status != EFI_SUCCESS)
+		goto fail_free_new_fdt;
+
+	status = update_fdt(sys_table, (void *)fdt_addr, fdt_size,
+			    (void *)*new_fdt_addr, MAX_FDT_SIZE, cmdline_ptr,
+			    initrd_addr, initrd_size);
+
+	if (status != EFI_SUCCESS) {
 		pr_efi_err(sys_table, "Unable to construct new device tree.\n");
 		goto fail_free_new_fdt;
 	}
-	}
 
 	priv.runtime_map = runtime_map;
 	priv.runtime_entry_count = &runtime_entry_count;
@@ -340,7 +331,7 @@ efi_status_t allocate_new_fdt_and_exit_boot(efi_system_table_t *sys_table,
 	pr_efi_err(sys_table, "Exit boot services failed.\n");
 
 fail_free_new_fdt:
-	efi_free(sys_table, new_fdt_size, *new_fdt_addr);
+	efi_free(sys_table, MAX_FDT_SIZE, *new_fdt_addr);
 
 fail:
 	sys_table->boottime->free_pool(runtime_map);