[PATCH v8 1/2] efi: Introduce efi_memdesc_ptr to get pointer to memmap descriptor

Baoquan He
2017-08-04T07:27:07Z

The existing map iteration helper for_each_efi_memory_desc_in_map can
only be used after OS initializes EFI to fill data of struct efi_memory_map.
Before that we also need iterate map descriptors which are stored in several
intermediate structures, like struct efi_boot_memmap for arch independent
usage and struct efi_info for x86 ARCH only.

Introduce efi_memdesc_ptr to get pointer to a map descriptor, and replace
several places of open code with it.

Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Baoquan He <bhe@redhat.com>
---
arch/x86/boot/compressed/eboot.c | 2 +-
drivers/firmware/efi/libstub/efi-stub-helper.c | 4 ++--
include/linux/efi.h | 19 +++++++++++++++++++
3 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/arch/x86/boot/compressed/eboot.c b/arch/x86/boot/compressed/eboot.c
index c3e869eaef0c..31e12b43be77 100644
--- a/arch/x86/boot/compressed/eboot.c
+++ b/arch/x86/boot/compressed/eboot.c
@@ -767,7 +767,7 @@ static efi_status_t setup_e820(struct boot_params *params,
m |= (u64)efi->efi_memmap_hi << 32;
#endif

- d = (efi_memory_desc_t *)(m + (i * efi->efi_memdesc_size));
+ d = efi_memdesc_ptr(m, efi->efi_memdesc_size, i);
switch (d->type) {
case EFI_RESERVED_TYPE:
case EFI_RUNTIME_SERVICES_CODE:
diff --git a/drivers/firmware/efi/libstub/efi-stub-helper.c b/drivers/firmware/efi/libstub/efi-stub-helper.c
index b0184360efc6..2db55c32e7ed 100644
--- a/drivers/firmware/efi/libstub/efi-stub-helper.c
+++ b/drivers/firmware/efi/libstub/efi-stub-helper.c
@@ -205,7 +205,7 @@ efi_status_t efi_high_alloc(efi_system_table_t *sys_table_arg,
unsigned long m = (unsigned long)map;
u64 start, end;

- desc = (efi_memory_desc_t *)(m + (i * desc_size));
+ desc = efi_memdesc_ptr(m, desc_size, i);
if (desc->type != EFI_CONVENTIONAL_MEMORY)
continue;

@@ -298,7 +298,7 @@ efi_status_t efi_low_alloc(efi_system_table_t *sys_table_arg,
unsigned long m = (unsigned long)map;
u64 start, end;

- desc = (efi_memory_desc_t *)(m + (i * desc_size));
+ desc = efi_memdesc_ptr(m, desc_size, i);

if (desc->type != EFI_CONVENTIONAL_MEMORY)
continue;
diff --git a/include/linux/efi.h b/include/linux/efi.h
index 8269bcb8ccf7..9a6ea328705f 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -1020,6 +1020,25 @@ extern int efi_memattr_init(void);
extern int efi_memattr_apply_permissions(struct mm_struct *mm,
efi_memattr_perm_setter fn);

+/*
+ * efi_memdesc_ptr - get the n-th efi memmap descriptor
+ * @map: the start of efi memmap
+ * @desc_size: the size of space for each efi memmap descriptor
+ * @n: the index of efi memmap descriptor
+ *
+ * EFI boot service provides function GetMemoryMap() to get a copy of the
+ * current memory map which is an array of memory descriptors, each of
+ * which describes a contiguous block of memory. And also get the size of
+ * map, and the size of each descriptor, etc. Note that per section 6.2 of
+ * UEFI Spec 2.6 Errata A, the returned size of each descriptor might not
+ * be equal to sizeof(efi_memory_memdesc_t) since efi_memory_memdesc_t may
+ * be extended in the future in response to hardware innovation. Thus OS
+ * MUST use the returned size of descriptor to find the start of each
+ * efi_memory_memdesc_t in the memory map array.
+ */
+#define efi_memdesc_ptr(map, desc_size, n) \
+ (efi_memory_desc_t *)((void *)(map) + ((n) * (desc_size)))
+
/* Iterate through an efi_memory_map */
#define for_each_efi_memory_desc_in_map(m, md) \
for ((md) = (m)->map; \
--
2.5.5