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

On 2026/08/13 09:45, Ard Biesheuvel wrote:
>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 <[email protected]>
>---
> 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
>
>

Reviewed-by: Richard Lyu <[email protected]>