By default, faulting kernel instruction that generates #AC due to split locked access is re-executed and doesn't block system.
But in cases when user doesn't tolerate any split lock (e.g. in hard real time system), CONFIG_SPLIT_LOCK_AC_PANIC_ON_KERNEL is added to opt-in panic when #AC for split lock is triggered from kernel. If it's configured as N (default), faulting instruction in kernel mode will be recorded in #AC handler and re-executed. Split lock is not treated as fatal fault. If configured as Y, kernel will panic if #AC triggered by split lock is from a kernel instruction. Signed-off-by: Fenghua Yu <[email protected]> --- arch/x86/Kconfig | 13 +++++++++++++ arch/x86/kernel/cpu/test_ctl.c | 15 +++++++++++++++ 2 files changed, 28 insertions(+) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 1d0dcd6fa69a..d42d90abd644 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -475,6 +475,19 @@ config SPLIT_LOCK_AC_ENABLE_DEFAULT Leave this to the default value of 2 if you are unsure. +config SPLIT_LOCK_AC_PANIC_ON_KERNEL + bool "Panic on #AC for split lock in kernel mode" + default n + depends on SPLIT_LOCK_AC + help + If you enable this option, kernel goes to panic when hitting + #AC for split lock from kernel. + + If you disable this option, the kernel faulting instruction + is re-executed after hitting #AC for split lock. + + Say N if unsure. + if X86_32 config X86_BIGSMP bool "Support for big SMP systems with more than 8 CPUs" diff --git a/arch/x86/kernel/cpu/test_ctl.c b/arch/x86/kernel/cpu/test_ctl.c index e8b3032f3db0..6784f68af26a 100644 --- a/arch/x86/kernel/cpu/test_ctl.c +++ b/arch/x86/kernel/cpu/test_ctl.c @@ -43,6 +43,14 @@ struct debugfs_file { const struct file_operations *fops; }; +enum { + KERNEL_MODE_RE_EXECUTE, + KERNEL_MODE_PANIC, + KERNEL_MODE_LAST +}; + +static int kernel_mode_reaction = KERNEL_MODE_RE_EXECUTE; + /* Detete feature of #AC for split lock by probing bit 29 in MSR_TEST_CTL. */ void detect_split_lock_ac(void) { @@ -238,6 +246,10 @@ bool do_split_lock_exception(struct pt_regs *regs, unsigned long error_code) struct task_struct *tsk = current; int cpu = task_cpu(tsk); + /* If configured as panic for split lock in kernel mode, panic. */ + if (kernel_mode_reaction == KERNEL_MODE_PANIC && !user_mode(regs)) + panic("Alignment Check exception for split lock in kernel."); + if (!re_execute(regs)) return false; @@ -391,6 +403,9 @@ static int __init split_lock_init(void) if (ret) pr_warn("debugfs for #AC for split lock cannot be set up\n"); + if (IS_ENABLED(CONFIG_SPLIT_LOCK_AC_PANIC_ON_KERNEL)) + kernel_mode_reaction = KERNEL_MODE_PANIC; + ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "x86/split_lock:online", split_lock_online, split_lock_offline); if (ret < 0) -- 2.5.0
