[PATCH v3 14/17] x86/efi: Reuse memory map instead of reallocating it

Ard Biesheuvel
2026-04-23T15:21:16Z

The EFI memory map consists of 10s to 100s of entries of around 40 bytes
each. The initial version is allocated and populated by the EFI stub,
but later on, after freeing the boot services data regions and pruning
the associated entries, a new memory map is allocated with room for only
the remaining entries, which are typically much fewer in number.

Given that the original allocation is never freed, this does not
actually save any memory currently, and it is much simpler to just move
the entries that need to be preserved to the beginning of the map, and
truncate it. That way, a lot of the complicated memory map allocation
and freeing code can simply be dropped.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/x86/include/asm/efi.h | 5 -
arch/x86/platform/efi/Makefile | 2 +-
arch/x86/platform/efi/memmap.c | 109 --------------------
arch/x86/platform/efi/quirks.c | 35 +------
include/linux/efi.h | 5 +-
5 files changed, 7 insertions(+), 149 deletions(-)

diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
index 7d8f627805df..0de92193764b 100644
--- a/arch/x86/include/asm/efi.h
+++ b/arch/x86/include/asm/efi.h
@@ -398,11 +398,6 @@ static inline void efi_reserve_boot_services(void)
}
#endif /* CONFIG_EFI */

-extern int __init efi_memmap_alloc(unsigned int num_entries,
- struct efi_memory_map_data *data);
-
-extern int __init efi_memmap_install(struct efi_memory_map_data *data);
-
enum efi_secureboot_mode __x86_efi_boot_mode(void);

#define arch_efi_boot_mode __x86_efi_boot_mode()
diff --git a/arch/x86/platform/efi/Makefile b/arch/x86/platform/efi/Makefile
index 500cab4a7f7c..28772e046a1b 100644
--- a/arch/x86/platform/efi/Makefile
+++ b/arch/x86/platform/efi/Makefile
@@ -2,7 +2,7 @@
KASAN_SANITIZE := n
GCOV_PROFILE := n

-obj-$(CONFIG_EFI) += memmap.o quirks.o efi.o efi_$(BITS).o \
+obj-$(CONFIG_EFI) += quirks.o efi.o efi_$(BITS).o \
efi_stub_$(BITS).o
obj-$(CONFIG_EFI_MIXED) += efi_thunk_$(BITS).o
obj-$(CONFIG_EFI_RUNTIME_MAP) += runtime-map.o
diff --git a/arch/x86/platform/efi/memmap.c b/arch/x86/platform/efi/memmap.c
deleted file mode 100644
index 524e9f2ef276..000000000000
--- a/arch/x86/platform/efi/memmap.c
+++ /dev/null
@@ -1,109 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0
-/*
- * Common EFI memory map functions.
- */
-
-#define pr_fmt(fmt) "efi: " fmt
-
-#include <linux/init.h>
-#include <linux/kernel.h>
-#include <linux/efi.h>
-#include <linux/io.h>
-#include <asm/early_ioremap.h>
-#include <asm/efi.h>
-#include <linux/memblock.h>
-#include <linux/slab.h>
-
-static phys_addr_t __init __efi_memmap_alloc_early(unsigned long size)
-{
- return memblock_phys_alloc(size, SMP_CACHE_BYTES);
-}
-
-static phys_addr_t __init __efi_memmap_alloc_late(unsigned long size)
-{
- unsigned int order = get_order(size);
- struct page *p = alloc_pages(GFP_KERNEL, order);
-
- if (!p)
- return 0;
-
- return PFN_PHYS(page_to_pfn(p));
-}
-
-static
-void __init __efi_memmap_free(u64 phys, unsigned long size, unsigned long flags)
-{
- if (flags & EFI_MEMMAP_MEMBLOCK) {
- memblock_phys_free(phys, size);
- } else if (flags & EFI_MEMMAP_SLAB) {
- struct page *p = pfn_to_page(PHYS_PFN(phys));
- unsigned int order = get_order(size);
-
- __free_pages(p, order);
- }
-}
-
-/**
- * efi_memmap_alloc - Allocate memory for the EFI memory map
- * @num_entries: Number of entries in the allocated map.
- * @data: efi memmap installation parameters
- *
- * Depending on whether mm_init() has already been invoked or not,
- * either memblock or "normal" page allocation is used.
- *
- * Returns zero on success, a negative error code on failure.
- */
-int __init efi_memmap_alloc(unsigned int num_entries,
- struct efi_memory_map_data *data)
-{
- /* Expect allocation parameters are zero initialized */
- WARN_ON(data->phys_map || data->size);
-
- data->size = num_entries * efi.memmap.desc_size;
- data->desc_version = efi.memmap.desc_version;
- data->desc_size = efi.memmap.desc_size;
- data->flags &= ~(EFI_MEMMAP_SLAB | EFI_MEMMAP_MEMBLOCK);
- data->flags |= efi.memmap.flags & EFI_MEMMAP_LATE;
-
- if (slab_is_available()) {
- data->flags |= EFI_MEMMAP_SLAB;
- data->phys_map = __efi_memmap_alloc_late(data->size);
- } else {
- data->flags |= EFI_MEMMAP_MEMBLOCK;
- data->phys_map = __efi_memmap_alloc_early(data->size);
- }
-
- if (!data->phys_map)
- return -ENOMEM;
- return 0;
-}
-
-/**
- * efi_memmap_install - Install a new EFI memory map in efi.memmap
- * @data: efi memmap installation parameters
- *
- * Unlike efi_memmap_init_*(), this function does not allow the caller
- * to switch from early to late mappings. It simply uses the existing
- * mapping function and installs the new memmap.
- *
- * Returns zero on success, a negative error code on failure.
- */
-int __init efi_memmap_install(struct efi_memory_map_data *data)
-{
- unsigned long size = efi.memmap.map_end - efi.memmap.map;
- unsigned long flags = efi.memmap.flags;
- u64 phys = efi.memmap.phys_map;
- int ret;
-
- efi_memmap_unmap();
-
- if (efi_enabled(EFI_PARAVIRT))
- return 0;
-
- ret = __efi_memmap_init(data);
- if (ret)
- return ret;
-
- __efi_memmap_free(phys, size, flags);
- return 0;
-}
diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
index eb00130bcb66..98fdc286eb40 100644
--- a/arch/x86/platform/efi/quirks.c
+++ b/arch/x86/platform/efi/quirks.c
@@ -401,10 +401,8 @@ static int __init efi_add_range_to_free(u64 range_start, u64 range_end,

void __init efi_unmap_boot_services(void)
{
- struct efi_memory_map_data data = { 0 };
efi_memory_desc_t *md;
- int num_entries = 0;
- void *new, *new_md;
+ void *new_md;

/* Keep all regions for /sys/kernel/debug/efi */
if (efi_enabled(EFI_DBG))
@@ -425,7 +423,6 @@ void __init efi_unmap_boot_services(void)

if (md->type != EFI_BOOT_SERVICES_CODE &&
md->type != EFI_BOOT_SERVICES_DATA) {
- num_entries++;
continue;
}

@@ -438,7 +435,6 @@ void __init efi_unmap_boot_services(void)

/* Do not free, someone else owns it: */
if (md->attribute & EFI_MEMORY_RUNTIME) {
- num_entries++;
continue;
}

@@ -452,23 +448,6 @@ void __init efi_unmap_boot_services(void)
pr_err("Failed to reallocate storage for freeable EFI regions\n");
return;
}
-
- if (has_reservations)
- num_entries++;
- }
-
- if (!num_entries)
- return;
-
- if (efi_memmap_alloc(num_entries, &data) != 0) {
- pr_err("Failed to allocate new EFI memmap\n");
- return;
- }
-
- new = memremap(data.phys_map, data.size, MEMREMAP_WB);
- if (!new) {
- pr_err("Failed to map new EFI memmap\n");
- return;
}

/*
@@ -476,7 +455,7 @@ void __init efi_unmap_boot_services(void)
* regions that are not tagged EFI_MEMORY_RUNTIME, since those
* regions have now been freed.
*/
- new_md = new;
+ new_md = efi.memmap.map;
for_each_efi_memory_desc(md) {
if (!(md->attribute & EFI_MEMORY_RUNTIME) &&
(md->type == EFI_BOOT_SERVICES_CODE ||
@@ -486,16 +465,12 @@ void __init efi_unmap_boot_services(void)
continue;
}

- memcpy(new_md, md, efi.memmap.desc_size);
+ if (new_md != md)
+ memcpy(new_md, md, efi.memmap.desc_size);
new_md += efi.memmap.desc_size;
}

- memunmap(new);
-
- if (efi_memmap_install(&data) != 0) {
- pr_err("Could not install new EFI memmap\n");
- return;
- }
+ efi.memmap.num_valid_entries = (new_md - efi.memmap.map) / efi.memmap.desc_size;
}

static int __init efi_free_boot_services(void)
diff --git a/include/linux/efi.h b/include/linux/efi.h
index a8406ca92332..5986e565a249 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -553,8 +553,7 @@ struct efi_unaccepted_memory {

/*
* Architecture independent structure for describing a memory map for the
- * benefit of efi_memmap_init_early(), and for passing context between
- * efi_memmap_alloc() and efi_memmap_install().
+ * benefit of efi_memmap_init_early().
*/
struct efi_memory_map_data {
phys_addr_t phys_map;
@@ -572,8 +571,6 @@ struct efi_memory_map {
unsigned long desc_version;
unsigned long desc_size;
#define EFI_MEMMAP_LATE (1UL << 0)
-#define EFI_MEMMAP_MEMBLOCK (1UL << 1)
-#define EFI_MEMMAP_SLAB (1UL << 2)
unsigned long flags;
};