efi/libstub: Add API function to allocate aligned memory

Break out the code to create an aligned page allocation from mem.c
and move it into a function efi_allocate_pages_aligned() in alignedmem.c.
Update efi_allocate_pages() to invoke it unless the minimum alignment
equals the EFI page size (4 KB), in which case the ordinary page
allocator is sufficient. This way, efi_allocate_pages_aligned() will
only be pulled into the build if it is actually being used (which will
be on arm64 only in the immediate future)

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

drivers/firmware/efi/libstub/Makefile

@@ -42,7 +42,8 @@ KCOV_INSTRUMENT			:= n
 
 lib-y				:= efi-stub-helper.o gop.o secureboot.o tpm.o \
 				   file.o mem.o random.o randomalloc.o pci.o \
-				   skip_spaces.o lib-cmdline.o lib-ctype.o
+				   skip_spaces.o lib-cmdline.o lib-ctype.o \
+				   alignedmem.o
 
 # include the stub's generic dependencies from lib/ when building for ARM/arm64
 efi-deps-y := fdt_rw.c fdt_ro.c fdt_wip.c fdt.c fdt_empty_tree.c fdt_sw.c

drivers/firmware/efi/libstub/alignedmem.c

@@ -0,0 +1,57 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/efi.h>
+#include <asm/efi.h>
+
+#include "efistub.h"
+
+/**
+ * efi_allocate_pages_aligned() - Allocate memory pages
+ * @size:	minimum number of bytes to allocate
+ * @addr:	On return the address of the first allocated page. The first
+ *		allocated page has alignment EFI_ALLOC_ALIGN which is an
+ *		architecture dependent multiple of the page size.
+ * @max:	the address that the last allocated memory page shall not
+ *		exceed
+ * @align:	minimum alignment of the base of the allocation
+ *
+ * Allocate pages as EFI_LOADER_DATA. The allocated pages are aligned according
+ * to @align, which should be >= EFI_ALLOC_ALIGN. The last allocated page will
+ * not exceed the address given by @max.
+ *
+ * Return:	status code
+ */
+efi_status_t efi_allocate_pages_aligned(unsigned long size, unsigned long *addr,
+					unsigned long max, unsigned long align)
+{
+	efi_physical_addr_t alloc_addr;
+	efi_status_t status;
+	int slack;
+
+	if (align < EFI_ALLOC_ALIGN)
+		align = EFI_ALLOC_ALIGN;
+
+	alloc_addr = ALIGN_DOWN(max + 1, align) - 1;
+	size = round_up(size, EFI_ALLOC_ALIGN);
+	slack = align / EFI_PAGE_SIZE - 1;
+
+	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;
+
+	*addr = ALIGN((unsigned long)alloc_addr, align);
+
+	if (slack > 0) {
+		int l = (alloc_addr % align) / EFI_PAGE_SIZE;
+
+		if (l) {
+			efi_bs_call(free_pages, alloc_addr, slack - l + 1);
+			slack = l - 1;
+		}
+		if (slack)
+			efi_bs_call(free_pages, *addr + size, slack);
+	}
+	return EFI_SUCCESS;
+}

drivers/firmware/efi/libstub/efistub.h

@@ -657,6 +657,9 @@ efi_status_t efi_low_alloc(unsigned long size, unsigned long align,
 efi_status_t efi_allocate_pages(unsigned long size, unsigned long *addr,
 				unsigned long max);
 
+efi_status_t efi_allocate_pages_aligned(unsigned long size, unsigned long *addr,
+					unsigned long max, unsigned long align);
+
 efi_status_t efi_relocate_kernel(unsigned long *image_addr,
 				 unsigned long image_size,
 				 unsigned long alloc_size,

drivers/firmware/efi/libstub/mem.c

@@ -93,31 +93,24 @@ fail:
 efi_status_t efi_allocate_pages(unsigned long size, unsigned long *addr,
 				unsigned long max)
 {
-	efi_physical_addr_t alloc_addr = ALIGN_DOWN(max + 1, EFI_ALLOC_ALIGN) - 1;
+	efi_physical_addr_t alloc_addr;
-	int slack = EFI_ALLOC_ALIGN / EFI_PAGE_SIZE - 1;
 	efi_status_t status;
 
-	size = round_up(size, EFI_ALLOC_ALIGN);
+	if (EFI_ALLOC_ALIGN > EFI_PAGE_SIZE)
+		return efi_allocate_pages_aligned(size, addr, max,
+						  EFI_ALLOC_ALIGN);
+
+	alloc_addr = ALIGN_DOWN(max + 1, EFI_ALLOC_ALIGN) - 1;
 	status = efi_bs_call(allocate_pages, EFI_ALLOCATE_MAX_ADDRESS,
-			     EFI_LOADER_DATA, size / EFI_PAGE_SIZE + slack,
+			     EFI_LOADER_DATA, DIV_ROUND_UP(size, EFI_PAGE_SIZE),
 			     &alloc_addr);
 	if (status != EFI_SUCCESS)
 		return status;
 
-	*addr = ALIGN((unsigned long)alloc_addr, EFI_ALLOC_ALIGN);
+	*addr = alloc_addr;
-
-	if (slack > 0) {
-		int l = (alloc_addr % EFI_ALLOC_ALIGN) / EFI_PAGE_SIZE;
-
-		if (l) {
-			efi_bs_call(free_pages, alloc_addr, slack - l + 1);
-			slack = l - 1;
-		}
-		if (slack)
-			efi_bs_call(free_pages, *addr + size, slack);
-	}
 	return EFI_SUCCESS;
 }
+
 /**
  * efi_low_alloc_above() - allocate pages at or above given address
  * @size:	size of the memory area to allocate