Patch "x86/efi: Disable runtime services on kexec kernel if booted with efi=old_map" has been added to the 4.9-stable tree

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

x86/efi: Disable runtime services on kexec kernel if booted with efi=old_map

to the 4.9-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:
x86-efi-disable-runtime-services-on-kexec-kernel-if-booted-with-efi-old_map.patch
and it can be found in the queue-4.9 subdirectory.

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

From: Sai Praneeth <[email protected]>
Date: Fri, 26 May 2017 12:36:49 +0100
Subject: x86/efi: Disable runtime services on kexec kernel if booted with efi=old_map

From: Sai Praneeth <[email protected]>

[ Upstream commit 4e52797d2efefac3271abdc54439a3435abd77b9 ]

Booting kexec kernel with "efi=old_map" in kernel command line hits kernel panic as shown below.

 BUG: unable to handle kernel paging request at ffff88007fe78070
 IP: virt_efi_set_variable.part.7+0x63/0x1b0
 PGD 7ea28067
 PUD 7ea2b067
 PMD 7ea2d067
 PTE 0
 [...]
 Call Trace:
  virt_efi_set_variable()
  efi_delete_dummy_variable()
  efi_enter_virtual_mode()
  start_kernel()
  x86_64_start_reservations()
  x86_64_start_kernel()
  start_cpu()

[ efi=old_map was never intended to work with kexec. The problem with
using efi=old_map is that the virtual addresses are assigned from the memory region used by other kernel mappings; vmalloc() space. Potentially there could be collisions when booting kexec if something else is mapped at the virtual address we allocated for runtime service regions in the initial boot - Matt Fleming ]

Since kexec was never intended to work with efi=old_map, disable runtime services in kexec if booted with efi=old_map, so that we don't panic.

---
 arch/x86/platform/efi/efi.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

@@ -832,9 +832,11 @@ static void __init kexec_enter_virtual_m
 
 	/*
 	 * We don't do virtual mode, since we don't do runtime services, on
-	 * non-native EFI
+	 * non-native EFI. With efi=old_map, we don't do runtime services in
+	 * kexec kernel because in the initial boot something else might
+	 * have been mapped at these virtual addresses.
 	 */
-	if (!efi_is_native()) {
+	if (!efi_is_native() || efi_enabled(EFI_OLD_MEMMAP)) {
 		efi_memmap_unmap();
 		clear_bit(EFI_RUNTIME_SERVICES, &efi.flags);
 		return;

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

queue-4.9/x86-efi-disable-runtime-services-on-kexec-kernel-if-booted-with-efi-old_map.patch