[PATCH] efi: Fix the size not consistent issue when unmapping memory map

[Lee, Chun-Yi]

When using kdump, SOMETIMES the "size not consistent" warning message
shows up when the crash kernel boots with early_ioremap_debug parameter:

WARNING: CPU: 0 PID: 0 at ../mm/early_ioremap.c:182 early_iounmap+0x4f/0x12c()
early_iounmap(ffffffffff200180, 00000118) [0] size not consistent 00000120

The root cause is that the unmapping size of memory map doesn't
match with the original size when mapping:

in __efi_memmap_init()
	map.map = early_memremap(phys_map, data->size);

in efi_memmap_unmap()
        size = efi.memmap.desc_size * efi.memmap.nr_map;
        early_memunmap(efi.memmap.map, size);

But the efi.memmap.nr_map is from __efi_memmap_init(). The remainder
of size was discarded when calculating the nr_map:
        map.nr_map = data->size / data->desc_size;

When the original size of memory map region does not equal to the
result of multiplication. The "size not consistent" warning
will be triggered.

This issue sometimes was hit by kdump because kexec set the efi map
size to align with 16 when loading crash kernel image:

in bzImage64_load()
        efi_map_sz = efi_get_runtime_map_size();
        efi_map_sz = ALIGN(efi_map_sz, 16);

Dave Young's a841aa83d patch fixed kexec issue. On UEFI side, this
patch changes the logic in the unmapping function. Using the end
address of map to calcuate original size.

Thank Randy Wright for his report and testing. And also thank
Takashi Iwai for his help to trace issue.

Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
Cc: Takashi Iwai <tiwai@xxxxxxx>
Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Tested-by: Randy Wright <rwright@xxxxxxx>
Signed-off-by: "Lee, Chun-Yi" <jlee@xxxxxxxx>
---
 drivers/firmware/efi/memmap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/firmware/efi/memmap.c b/drivers/firmware/efi/memmap.c
index 5fc7052..1f592d8 100644
--- a/drivers/firmware/efi/memmap.c
+++ b/drivers/firmware/efi/memmap.c
@@ -121,7 +121,7 @@ void __init efi_memmap_unmap(void)
 	if (!efi.memmap.late) {
 		unsigned long size;
 
-		size = efi.memmap.desc_size * efi.memmap.nr_map;
+		size = efi.memmap.map_end - efi.memmap.map;
 		early_memunmap(efi.memmap.map, size);
 	} else {
 		memunmap(efi.memmap.map);
-- 
2.10.2