[tip:efi/urgent] efi/arm: Fix boot crash with CONFIG_CPUMASK_OFFSTACK=y

[tip-bot for Ard Biesheuvel]

Commit-ID:  d1eb98143c56f24fef125f5bbed49ae0b52fb7d6
Gitweb:     http://git.kernel.org/tip/d1eb98143c56f24fef125f5bbed49ae0b52fb7d6
Author:     Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
AuthorDate: Wed, 1 Mar 2017 19:05:54 +0000
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 2 Mar 2017 08:11:19 +0100

efi/arm: Fix boot crash with CONFIG_CPUMASK_OFFSTACK=y

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.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # v4.5+
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: linux-efi@xxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/1488395154-29786-1-git-send-email-ard.biesheuvel@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 drivers/firmware/efi/arm-runtime.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/firmware/efi/arm-runtime.c b/drivers/firmware/efi/arm-runtime.c
index 349dc3e..974c5a3 100644
--- a/drivers/firmware/efi/arm-runtime.c
+++ b/drivers/firmware/efi/arm-runtime.c
@@ -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;