efi: Add efi_memmap_init_late() for permanent EFI memmap

Drivers need a way to access the EFI memory map at runtime. ARM and
arm64 currently provide this by remapping the EFI memory map into the
vmalloc space before setting up the EFI virtual mappings.

x86 does not provide this functionality which has resulted in the code
in efi_mem_desc_lookup() where it will manually map individual EFI
memmap entries if the memmap has already been torn down on x86,

  /*
   * If a driver calls this after efi_free_boot_services,
   * ->map will be NULL, and the target may also not be mapped.
   * So just always get our own virtual map on the CPU.
   *
   */
  md = early_memremap(p, sizeof (*md));

There isn't a good reason for not providing a permanent EFI memory map
for runtime queries, especially since the EFI regions are not mapped
into the standard kernel page tables.

Tested-by: Dave Young <dyoung@redhat.com> [kexec/kdump]
Tested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> [arm]
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Leif Lindholm <leif.lindholm@linaro.org>
Cc: Peter Jones <pjones@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/efi.h b/include/linux/efi.h
index d862d4998580..f149676b2fcd 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -688,6 +688,7 @@ struct efi_memory_map {
 	int nr_map;
 	unsigned long desc_version;
 	unsigned long desc_size;
+	bool late;
 };
 
 struct efi_fdt_params {
@@ -914,6 +915,7 @@ static inline efi_status_t efi_query_variable_store(u32 attributes,
 extern void __iomem *efi_lookup_mapped_addr(u64 phys_addr);
 
 extern int __init efi_memmap_init_early(struct efi_memory_map_data *data);
+extern int __init efi_memmap_init_late(phys_addr_t addr, unsigned long size);
 extern void __init efi_memmap_unmap(void);
 
 extern int efi_config_init(efi_config_table_type_t *arch_tables);