[PATCH v3 03/17] x86/efi: Only merge EFI memory map entries on 32-bit systems

Ard Biesheuvel
2026-04-23T15:21:04Z

Commit

202f9d0a4180 ("x86, efi: Merge contiguous memory regions of the same type and attribute")

introduced a pass over the EFI memory map, ensuring that contiguous
regions of the same type and attribute are coalesced into a single
entry. This was needed because relative references may exist between
those regions, and so the virtual remapping needs to preserve the
relative placement of these regions. This virtual remapping was based on
ioremap() at the time, which does not guarantee that adjacent physical
addresses are mapped adjacently in the virtual space.

Commit

d2f7cbe7b26a ("x86/efi: Runtime services virtual mapping")

introduced a new strategy for virtually remapping the EFI runtime
services, which is now the only remaining one, and commit

a5caa209ba9c ("x86/efi: Fix boot crash by mapping EFI memmap entries bottom-up at runtime, instead of top-down")

tweaked the logic to ensure that the relative offset of adjacent regions
of any type is preserved on 64-bit systems, by reversing the order in
which the EFI memory map is traversed when choosing the virtual
placement.

This means that merging regions is no longer needed on 64-bit, given
that the relative placement of adjacent regions is guaranteed to be
preserved in the virtual space. So make this hack 32-bit only.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/x86/include/asm/efi.h | 6 ++++
arch/x86/platform/efi/efi.c | 31 --------------------
arch/x86/platform/efi/efi_32.c | 31 ++++++++++++++++++++
3 files changed, 37 insertions(+), 31 deletions(-)

diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
index dc8fe1361c18..f291845b403a 100644
--- a/arch/x86/include/asm/efi.h
+++ b/arch/x86/include/asm/efi.h
@@ -143,6 +143,12 @@ extern void efi_unmap_boot_services(void);
void arch_efi_call_virt_setup(void);
void arch_efi_call_virt_teardown(void);

+#ifdef CONFIG_X86_32
+void efi_merge_regions(void);
+#else
+static inline void efi_merge_regions(void) {}
+#endif
+
extern u64 efi_setup;

#ifdef CONFIG_EFI
diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
index 1b7a0cd54d08..c0195b5eab21 100644
--- a/arch/x86/platform/efi/efi.c
+++ b/arch/x86/platform/efi/efi.c
@@ -502,37 +502,6 @@ void __init efi_init(void)
efi_print_memmap();
}

-/* Merge contiguous regions of the same type and attribute */
-static void __init efi_merge_regions(void)
-{
- efi_memory_desc_t *md, *prev_md = NULL;
-
- for_each_efi_memory_desc(md) {
- u64 prev_size;
-
- if (!prev_md) {
- prev_md = md;
- continue;
- }
-
- if (prev_md->type != md->type ||
- prev_md->attribute != md->attribute) {
- prev_md = md;
- continue;
- }
-
- prev_size = prev_md->num_pages << EFI_PAGE_SHIFT;
-
- if (md->phys_addr == (prev_md->phys_addr + prev_size)) {
- prev_md->num_pages += md->num_pages;
- md->type = EFI_RESERVED_TYPE;
- md->attribute = 0;
- continue;
- }
- prev_md = md;
- }
-}
-
static void *realloc_pages(void *old_memmap, int old_shift)
{
void *ret;
diff --git a/arch/x86/platform/efi/efi_32.c b/arch/x86/platform/efi/efi_32.c
index b2cc7b4552a1..886ede4117b5 100644
--- a/arch/x86/platform/efi/efi_32.c
+++ b/arch/x86/platform/efi/efi_32.c
@@ -152,3 +152,34 @@ void arch_efi_call_virt_teardown(void)
firmware_restrict_branch_speculation_end();
efi_fpu_end();
}
+
+/* Merge contiguous regions of the same type and attribute */
+void __init efi_merge_regions(void)
+{
+ efi_memory_desc_t *md, *prev_md = NULL;
+
+ for_each_efi_memory_desc(md) {
+ u64 prev_size;
+
+ if (!prev_md) {
+ prev_md = md;
+ continue;
+ }
+
+ if (prev_md->type != md->type ||
+ prev_md->attribute != md->attribute) {
+ prev_md = md;
+ continue;
+ }
+
+ prev_size = prev_md->num_pages << EFI_PAGE_SHIFT;
+
+ if (md->phys_addr == (prev_md->phys_addr + prev_size)) {
+ prev_md->num_pages += md->num_pages;
+ md->type = EFI_RESERVED_TYPE;
+ md->attribute = 0;
+ continue;
+ }
+ prev_md = md;
+ }
+}