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

Dave Young
2018-04-16T02:57:44Z

On 04/13/18 at 02:27pm, Lee, Chun-Yi wrote:
> 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);
>
> 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.

Good catch. The kexec code need to be fixed to use a separate buffer so
avoid the alignment like what kexec-tools did. I can submit a fix for
that.

But this issue could be a potential issue even if kexec get fixed so it
looks worth a fix in efi code as well. How about mapping only nr_maps
*desc_size in __efi_memmap_init? It looks easier to understand.

>
> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Cc: Randy Wright <rwright@hpe.com>
> Cc: Takashi Iwai <tiwai@suse.de>
> Cc: Vivek Goyal <vgoyal@redhat.com>
> Cc: Ingo Molnar <mingo@redhat.com>
> Signed-off-by: "Lee, Chun-Yi" <jlee@suse.com>
> ---
> 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
>
>
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Thanks
Dave