Patch "efi/arm: Fix boot crash with CONFIG_CPUMASK_OFFSTACK=y" has been added to the 4.10-stable tree

This is a note to let you know that I've just added the patch titled

efi/arm: Fix boot crash with CONFIG_CPUMASK_OFFSTACK=y

to the 4.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
efi-arm-fix-boot-crash-with-config_cpumask_offstack-y.patch
and it can be found in the queue-4.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Ard Biesheuvel <[email protected]>
Date: Wed, 1 Mar 2017 19:05:54 +0000
Subject: efi/arm: Fix boot crash with CONFIG_CPUMASK_OFFSTACK=y

From: Ard Biesheuvel <[email protected]>

commit d1eb98143c56f24fef125f5bbed49ae0b52fb7d6 upstream.

On ARM and arm64, we use a dedicated mm_struct to map the UEFI Runtime Services regions, which allows us to map those regions on demand, and in a way that is guaranteed to be compatible with incoming kernels across kexec.

As it turns out, we don't fully initialize the mm_struct in the same way as process mm_structs are initialized on fork(), which results in the following crash on ARM if CONFIG_CPUMASK_OFFSTACK=y is enabled:

...
EFI Variables Facility v0.08 2004-May-17

  Unable to handle kernel NULL pointer dereference at virtual address 00000000
  [...]
  Process swapper/0 (pid: 1)
  ...
  __memzero()
  check_and_switch_context()
  virt_efi_get_next_variable()
  efivar_init()
  efivars_sysfs_init()
  do_one_initcall()
  ...

This is due to a missing call to mm_init_cpumask(), so add it.

---
 drivers/firmware/efi/arm-runtime.c |    1 +
 1 file changed, 1 insertion(+)

@@ -65,6 +65,7 @@ static bool __init efi_virtmap_init(void
 	bool systab_found;
 
 	efi_mm.pgd = pgd_alloc(&efi_mm);
+	mm_init_cpumask(&efi_mm);
 	init_new_context(NULL, &efi_mm);
 
 	systab_found = false;

Patches currently in stable-queue which might be from [email protected] are

queue-4.10/efi-arm-fix-boot-crash-with-config_cpumask_offstack-y.patch