efi/libstub: Simplify efi_high_alloc() and rename to efi_allocate_pages()

The implementation of efi_high_alloc() uses a complicated way of
traversing the memory map to find an available region that is located
as close as possible to the provided upper limit, and calls AllocatePages
subsequently to create the allocation at that exact address.

This is precisely what the EFI_ALLOCATE_MAX_ADDRESS allocation type
argument to AllocatePages() does, and considering that EFI_ALLOC_ALIGN
only exceeds EFI_PAGE_SIZE on arm64, let's use AllocatePages() directly
and implement the alignment using code that the compiler can remove if
it does not exceed EFI_PAGE_SIZE.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

drivers/firmware/efi/libstub/efi-stub-helper.c

@@ -385,8 +385,7 @@ efi_status_t handle_cmdline_files(efi_loaded_image_t *image,
 		 * so allocate enough memory for all the files.  This is used
 		 * for loading multiple files.
 		 */
-		status = efi_high_alloc(file_size_total, 0x1000, &file_addr,
-					max_addr);
+		status = efi_allocate_pages(file_size_total, &file_addr, max_addr);
 		if (status != EFI_SUCCESS) {
 			pr_efi_err("Failed to alloc highmem for files\n");
 			goto close_handles;
@@ -536,7 +535,7 @@ char *efi_convert_cmdline(efi_loaded_image_t *image,
 
 	options_bytes++;	/* NUL termination */
 
-	status = efi_high_alloc(options_bytes, 0, &cmdline_addr,
+	status = efi_allocate_pages(options_bytes, &cmdline_addr,
 				MAX_CMDLINE_ADDRESS);
 	if (status != EFI_SUCCESS)
 		return NULL;

drivers/firmware/efi/libstub/fdt.c

@@ -277,8 +277,7 @@ efi_status_t allocate_new_fdt_and_exit_boot(void *handle,
 	pr_efi("Exiting boot services and installing virtual address map...\n");
 
 	map.map = &memory_map;
-	status = efi_high_alloc(MAX_FDT_SIZE, EFI_PAGE_SIZE,
-				new_fdt_addr, max_addr);
+	status = efi_allocate_pages(MAX_FDT_SIZE, new_fdt_addr, max_addr);
 	if (status != EFI_SUCCESS) {
 		pr_efi_err("Unable to allocate memory for new device tree.\n");
 		goto fail;

drivers/firmware/efi/libstub/mem.c

@@ -68,100 +68,34 @@ efi_status_t efi_get_memory_map(struct efi_boot_memmap *map)
 /*
  * Allocate at the highest possible address that is not above 'max'.
  */
-efi_status_t efi_high_alloc(unsigned long size, unsigned long align,
-			    unsigned long *addr, unsigned long max)
+efi_status_t efi_allocate_pages(unsigned long size, unsigned long *addr,
+				unsigned long max)
 {
-	unsigned long map_size, desc_size, buff_size;
-	efi_memory_desc_t *map;
+	efi_physical_addr_t alloc_addr = ALIGN_DOWN(max + 1, EFI_ALLOC_ALIGN) - 1;
+	int slack = EFI_ALLOC_ALIGN / EFI_PAGE_SIZE - 1;
 	efi_status_t status;
-	unsigned long nr_pages;
-	u64 max_addr = 0;
-	int i;
-	struct efi_boot_memmap boot_map;
-
-	boot_map.map =		↦
-	boot_map.map_size =	&map_size;
-	boot_map.desc_size =	&desc_size;
-	boot_map.desc_ver =	NULL;
-	boot_map.key_ptr =	NULL;
-	boot_map.buff_size =	&buff_size;
-
-	status = efi_get_memory_map(&boot_map);
-	if (status != EFI_SUCCESS)
-		goto fail;
-
-	/*
-	 * Enforce minimum alignment that EFI or Linux requires when
-	 * requesting a specific address.  We are doing page-based (or
-	 * larger) allocations, and both the address and size must meet
-	 * alignment constraints.
-	 */
-	if (align < EFI_ALLOC_ALIGN)
-		align = EFI_ALLOC_ALIGN;
 
 	size = round_up(size, EFI_ALLOC_ALIGN);
-	nr_pages = size / EFI_PAGE_SIZE;
-again:
-	for (i = 0; i < map_size / desc_size; i++) {
-		efi_memory_desc_t *desc;
-		unsigned long m = (unsigned long)map;
-		u64 start, end;
-
-		desc = efi_early_memdesc_ptr(m, desc_size, i);
-		if (desc->type != EFI_CONVENTIONAL_MEMORY)
-			continue;
-
-		if (efi_soft_reserve_enabled() &&
-		    (desc->attribute & EFI_MEMORY_SP))
-			continue;
-
-		if (desc->num_pages < nr_pages)
-			continue;
-
-		start = desc->phys_addr;
-		end = start + desc->num_pages * EFI_PAGE_SIZE;
-
-		if (end > max)
-			end = max;
-
-		if ((start + size) > end)
-			continue;
-
-		if (round_down(end - size, align) < start)
-			continue;
-
-		start = round_down(end - size, align);
+	status = efi_bs_call(allocate_pages, EFI_ALLOCATE_MAX_ADDRESS,
+			     EFI_LOADER_DATA, size / EFI_PAGE_SIZE + slack,
+			     &alloc_addr);
+	if (status != EFI_SUCCESS)
+		return status;
 
-		/*
-		 * Don't allocate at 0x0. It will confuse code that
-		 * checks pointers against NULL.
-		 */
-		if (start == 0x0)
-			continue;
+	*addr = ALIGN((unsigned long)alloc_addr, EFI_ALLOC_ALIGN);
 
-		if (start > max_addr)
-			max_addr = start;
-	}
+	if (slack > 0) {
+		int l = (alloc_addr % EFI_ALLOC_ALIGN) / EFI_PAGE_SIZE;
 
-	if (!max_addr)
-		status = EFI_NOT_FOUND;
-	else {
-		status = efi_bs_call(allocate_pages, EFI_ALLOCATE_ADDRESS,
-				     EFI_LOADER_DATA, nr_pages, &max_addr);
-		if (status != EFI_SUCCESS) {
-			max = max_addr;
-			max_addr = 0;
-			goto again;
+		if (l) {
+			efi_bs_call(free_pages, alloc_addr, slack - l + 1);
+			slack = l - 1;
 		}
-
-		*addr = max_addr;
+		if (slack)
+			efi_bs_call(free_pages, *addr + size, slack);
 	}
-
-	efi_bs_call(free_pool, map);
-fail:
-	return status;
+	return EFI_SUCCESS;
 }
-
 /*
  * Allocate at the lowest possible address that is not below 'min'.
  */

include/linux/efi.h

@@ -1508,8 +1508,8 @@ efi_status_t efi_low_alloc(unsigned long size, unsigned long align,
 	return efi_low_alloc_above(size, align, addr, 0x8);
 }
 
-efi_status_t efi_high_alloc(unsigned long size, unsigned long align,
-			    unsigned long *addr, unsigned long max);
+efi_status_t efi_allocate_pages(unsigned long size, unsigned long *addr,
+				unsigned long max);
 
 efi_status_t efi_relocate_kernel(unsigned long *image_addr,
 				 unsigned long image_size,