Sometimes user wants to test how split lock in kernel mode is process. debugfs interface /sys/kernel/debug/x86/split_lock/test_kernel is provided to do the test. The interface is enabled by CONFIG_SPLIT_LOCK_AC_TEST.
Writing 1 to the interface file triggers a split locked access in kernel and procedure of handling the split lock. The file is not readable. Signed-off-by: Fenghua Yu <[email protected]> --- arch/x86/Kconfig | 10 +++++++ arch/x86/kernel/cpu/test_ctl.c | 61 ++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 71 insertions(+) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index d42d90abd644..5d44cc86aecf 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -488,6 +488,16 @@ config SPLIT_LOCK_AC_PANIC_ON_KERNEL Say N if unsure. +config SPLIT_LOCK_AC_TEST + bool "Test #AC exception for split locked accesses" + default n + depends on SPLIT_LOCK_AC + help + Select to enable testing #AC exception for split lock accesses. + This adds interface /sys/kernel/debug/x86/split_lock/test_kernel + to allow user to trigger split locked access in kernel and test + split lock handling. + 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 8bdc01067be9..910ff19c2a3e 100644 --- a/arch/x86/kernel/cpu/test_ctl.c +++ b/arch/x86/kernel/cpu/test_ctl.c @@ -541,6 +541,64 @@ static int firmware_store(void *data, u64 val) DEFINE_DEBUGFS_ATTRIBUTE(firmware_ops, firmware_show, firmware_store, "%llx\n"); +#ifdef CONFIG_SPLIT_LOCK_AC_TEST +/* Execute locked btsl instruction with split lock operand. */ +static void split_lock_test_kernel(void) +{ + char cptr[128] __aligned(64); + int *iptr; + + /* + * Change the pointer, making it 3-byte away from the next cache + * line. + */ + iptr = (int *)(cptr + 61); + + /* Initial value 0 in iptr */ + *iptr = 0; + + pr_info("split lock test: split lock address=0x%lx\n", + (unsigned long)iptr); + + /* + * The distance between iptr and next cache line is 3 bytes. + * Operand size in "btsl" is 4 bytes. So iptr will span two cache + * lines. "lock btsl" instruction will trigger #AC in hardware + * and kernel will either re-execute the instruction or go to panic + * depending on user configuration in + * /sys/kernel/debug/x86/split_lock/kernel_mode. + */ + asm volatile ("lock btsl $0, %0\n\t" + : "=m" (*iptr)); + + if (*iptr == 1) + pr_info("split lock kernel test passes\n"); + else + pr_info("split lock kernel test fails\n"); +} + +/* + * Writing 1 to /sys/kernel/debug/x86/split_lock/test_kernel triggers + * split locke daccess in kernel mode. + */ +static int test_kernel_store(void *data, u64 val) +{ + if (split_lock_ac_kernel == DISABLE_SPLIT_LOCK_AC) + return -ENODEV; + + if (val != 1) + return -EINVAL; + + mutex_lock(&split_lock_mutex); + split_lock_test_kernel(); + mutex_unlock(&split_lock_mutex); + + return 0; +} + +DEFINE_DEBUGFS_ATTRIBUTE(test_kernel_ops, NULL, test_kernel_store, "%llx\n"); +#endif /* CONFIG_SPLIT_LOCK_AC_TEST */ + static int __init debugfs_setup_split_lock(void) { struct debugfs_file debugfs_files[] = { @@ -548,6 +606,9 @@ static int __init debugfs_setup_split_lock(void) {"kernel_mode", 0600, &kernel_mode_ops }, {"user_mode", 0600, &user_mode_ops }, {"firmware", 0600, &firmware_ops }, +#ifdef CONFIG_SPLIT_LOCK_AC_TEST + {"test_kernel", 0200, &test_kernel_ops }, +#endif }; struct dentry *split_lock_dir, *fd; int i; -- 2.5.0
