BIOS may contain split locked instructions. #AC handler in BIOS may treat split lock as fatal fault and stop execution. If kernel enables #AC exception for split locked accesses and then kernel returns to BIOS, the BIOS reboot code may hit #AC exception and block the reboot.
Instead of debugging the buggy BIOS, #AC setting for split lock is restored to original BIOS setting to hide the potential BIOS issue and allow kernel reboot succeed. Signed-off-by: Fenghua Yu <[email protected]> --- arch/x86/include/asm/cpu.h | 2 ++ arch/x86/kernel/cpu/split_lock.c | 56 ++++++++++++++++++++++++++++++++++++++-- 2 files changed, 56 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/cpu.h b/arch/x86/include/asm/cpu.h index 80dc27d73e81..0b00033b6fa8 100644 --- a/arch/x86/include/asm/cpu.h +++ b/arch/x86/include/asm/cpu.h @@ -44,10 +44,12 @@ unsigned int x86_stepping(unsigned int sig); int __init enumerate_split_lock(void); void setup_split_lock(void); bool do_split_lock_exception(struct pt_regs *regs, unsigned long error_code); +bool restore_split_lock_ac_bios(int *enable); #else /* CONFIG_SPLIT_LOCK_AC */ static inline int enumerate_split_lock(void) { return 0; } static inline void setup_split_lock(void) {} static inline bool do_split_lock_exception(struct pt_regs *regs, unsigned long error_code) {} +static inline bool restore_split_lock_ac_bios(int *enable) { return true; } #endif /* CONFIG_SPLIT_LOCK_AC */ #endif /* _ASM_X86_CPU_H */ diff --git a/arch/x86/kernel/cpu/split_lock.c b/arch/x86/kernel/cpu/split_lock.c index efe6f39353d1..d2735259800b 100644 --- a/arch/x86/kernel/cpu/split_lock.c +++ b/arch/x86/kernel/cpu/split_lock.c @@ -13,6 +13,7 @@ #include <linux/printk.h> #include <linux/workqueue.h> #include <linux/cpu.h> +#include <linux/reboot.h> #include <asm/msr.h> static bool split_lock_ac_supported; @@ -21,6 +22,7 @@ static bool split_lock_ac_supported; #define ENABLE_SPLIT_LOCK_AC 1 static int split_lock_ac = DISABLE_SPLIT_LOCK_AC; +static int split_lock_ac_bios = DISABLE_SPLIT_LOCK_AC; static DEFINE_SPINLOCK(sl_lock); @@ -71,10 +73,13 @@ void __init enumerate_split_lock(void) wrmsr(MSR_TEST_CTL, l_orig, h); /* Initialize split lock setting from previous BIOS setting. */ - if (l_orig & MSR_TEST_CTL_ENABLE_AC_SPLIT_LOCK) + if (l_orig & MSR_TEST_CTL_ENABLE_AC_SPLIT_LOCK) { + split_lock_ac_bios = ENABLE_SPLIT_LOCK_AC; split_lock_ac = ENABLE_SPLIT_LOCK_AC; - else + } else { + split_lock_ac_bios = DISABLE_SPLIT_LOCK_AC; split_lock_ac = DISABLE_SPLIT_LOCK_AC; + } pr_info("#AC exception for split locked accesses is supported\n"); } @@ -117,6 +122,44 @@ static bool _setup_split_lock(int split_lock_ac_val) return false; } +static bool restore_split_lock_ac(int split_lock_ac_val) +{ + if (!_setup_split_lock(split_lock_ac_val)) + return false; + + return true; +} + +/* Restore BIOS setting for #AC exception for split lock. */ +bool restore_split_lock_ac_bios(int *enable) +{ + /* Don't restore the BIOS setting if kernel didn't change it. */ + if (split_lock_ac == split_lock_ac_bios) + return false; + + if (enable) + *enable = split_lock_ac_bios == ENABLE_SPLIT_LOCK_AC ? 1 : 0; + + return restore_split_lock_ac(split_lock_ac_bios); +} + +static void split_lock_cpu_reboot(void *unused) +{ + restore_split_lock_ac_bios(NULL); +} + +static int split_lock_reboot_notify(struct notifier_block *nb, + unsigned long code, void *unused) +{ + on_each_cpu_mask(cpu_online_mask, split_lock_cpu_reboot, NULL, 1); + + return NOTIFY_DONE; +} + +static struct notifier_block split_lock_reboot_nb = { + .notifier_call = split_lock_reboot_notify, +}; + void setup_split_lock(void) { if (!split_lock_ac_supported) @@ -179,3 +222,12 @@ bool do_split_lock_exception(struct pt_regs *regs, unsigned long error_code) return true; } + +static int __init split_lock_init(void) +{ + register_reboot_notifier(&split_lock_reboot_nb); + + return 0; +} + +late_initcall(split_lock_init); -- 2.5.0
