[PATCH 3/3] efi: Make the 'linux,uefi-boot-memmap' DT property optional

[Ard Biesheuvel <ardb@kernel.org>]

The 'linux,uefi-boot-memmap DT property' is redundant in principle,
given that it carries a physical address that is also passed via a EFI
config table entry.

However, if SetVirtualAddressMap() has been called, the address of the
config table array has been translated to virtual, and so the memory map
is needed to translate it back to physical before it can be located.

This means that passing the linux,uefi-boot-memmap DT property is only
needed if SetVirtualAddressMap() has been called, which is a terrible
idea anyway, and if it has not been called, the config table array can
simply be parsed to look for LINUX_EFI_BOOT_MEMMAP_TABLE_GUID, and the
address taken from there.

So permit this, and make the boot memmap property optional.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 drivers/firmware/efi/fdtparams.c | 42 ++++++++++++++++++--
 1 file changed, 38 insertions(+), 4 deletions(-)

diff --git a/drivers/firmware/efi/fdtparams.c b/drivers/firmware/efi/fdtparams.c
index a54a76a6aaeb..89ffccf35fd7 100644
--- a/drivers/firmware/efi/fdtparams.c
+++ b/drivers/firmware/efi/fdtparams.c
@@ -89,14 +89,15 @@ static int __init efi_get_fdt_prop(const void *fdt, int node, const char *pname,
 u64 __init efi_get_fdt_params(struct efi_memory_map_data *mm)
 {
 	const void *fdt = initial_boot_params;
-	unsigned long systab, memmap;
+	unsigned long systab, memmap = 0;
 	int i, j, node;
 	struct {
 		void	*var;
 		int	size;
+		int	optional;
 	} target[] = {
 		[SYSTAB] = { &systab,		sizeof(systab) },
-		[MEMMAP] = { &memmap,		sizeof(memmap) },
+		[MEMMAP] = { &memmap,		sizeof(memmap), 1 },
 #ifdef CONFIG_XEN
 		[MMBASE] = { &mm->phys_map,	sizeof(mm->phys_map) },
 		[MMSIZE] = { &mm->size,		sizeof(mm->size) },
@@ -131,14 +132,47 @@ u64 __init efi_get_fdt_params(struct efi_memory_map_data *mm)
 				continue;
 			if (!j)
 				goto notfound;
-			pr_err("Can't find property '%s' in DT!\n", pname);
-			return 0;
+			if (!target[j].optional) {
+				pr_err("Can't find property '%s' in DT!\n", pname);
+				return 0;
+			}
 		}
 		if (IS_ENABLED(CONFIG_XEN) && dt_params[i].paravirt) {
 			set_bit(EFI_PARAVIRT, &efi.flags);
 		} else {
 			struct efi_boot_memmap *bm;
 
+			if (!memmap) {
+				unsigned long tables, nr_tables;
+				efi_system_table_t *st;
+				efi_config_table_t *tbl;
+
+				st = early_memremap_ro(systab, sizeof(*st));
+				if (!st) {
+					pr_err("Cannot remap EFI system table\n");
+					return 0;
+				}
+
+				tables		= st->tables;
+				nr_tables	= st->nr_tables;
+
+				early_memunmap(st, sizeof(*st));
+
+				tbl = early_memremap_ro(tables, sizeof(*tbl) * nr_tables);
+				if (!tbl) {
+					pr_err("Cannot remap EFI config table array\n");
+					return 0;
+				}
+
+				for (int i = 0; i < nr_tables; i++) {
+					if (!efi_guidcmp(tbl[i].guid, LINUX_EFI_BOOT_MEMMAP_GUID)) {
+						memmap = (unsigned long)tbl[i].table;
+						break;
+					}
+				}
+				early_memunmap(tbl, sizeof(*tbl) * nr_tables);
+			}
+
 			bm = early_memremap_ro(memmap, sizeof(*bm));
 			if (!bm) {
 				pr_err("Cannot remap EFI boot memory map\n");
-- 
2.47.3