[RFC PATCH 08/16] x86/split_lock: Set split lock during EFI runtime service

[Fenghua Yu]

If kernel enables #AC for split locked accesses, EFI runtime service may
hit #AC exception, treat it as fatal fault, and cause system hang.

To avoid debugging potential buggy EFI runtime service code in firmware,
restore to firmware split lock setting before entering EFI runtime service
and restore to kernel split lock setting after exiting EFI runtime service.

Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
---
 arch/x86/include/asm/efi.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
index cec5fae23eb3..a5604e5a56c1 100644
--- a/arch/x86/include/asm/efi.h
+++ b/arch/x86/include/asm/efi.h
@@ -8,6 +8,7 @@
 #include <asm/tlb.h>
 #include <asm/nospec-branch.h>
 #include <asm/mmu_context.h>
+#include <asm/cpu.h>
 
 /*
  * We map the EFI regions needed for runtime services non-contiguously,
@@ -41,12 +42,14 @@ extern asmlinkage unsigned long efi_call_phys(void *, ...);
 #define arch_efi_call_virt_setup()					\
 ({									\
 	kernel_fpu_begin();						\
+	restore_split_lock_ac_firmware();				\
 	firmware_restrict_branch_speculation_start();			\
 })
 
 #define arch_efi_call_virt_teardown()					\
 ({									\
 	firmware_restrict_branch_speculation_end();			\
+	restore_split_lock_ac_kernel();				\
 	kernel_fpu_end();						\
 })
 
@@ -84,6 +87,7 @@ struct efi_scratch {
 	efi_sync_low_kernel_mappings();					\
 	preempt_disable();						\
 	__kernel_fpu_begin();						\
+	restore_split_lock_ac_firmware();				\
 	firmware_restrict_branch_speculation_start();			\
 									\
 	if (!efi_enabled(EFI_OLD_MEMMAP))				\
@@ -99,6 +103,7 @@ struct efi_scratch {
 		efi_switch_mm(efi_scratch.prev_mm);			\
 									\
 	firmware_restrict_branch_speculation_end();			\
+	restore_split_lock_ac_kernel();				\
 	__kernel_fpu_end();						\
 	preempt_enable();						\
 })
-- 
2.5.0