CONFIG_SPLIT_LOCK_AC_TEST is added to enable sysfs interface /sys/kernel/split_lock/test_kernel to test split lock in kernel.
Writing 1 to the file triggers a split locked access in kernel. User can use this interface to test how split locked access happening in kernel is handled. The file is not readable. Signed-off-by: Fenghua Yu <[email protected]> --- arch/x86/Kconfig | 10 ++++++ arch/x86/kernel/cpu/split_lock.c | 71 ++++++++++++++++++++++++++++++++++++++++ 2 files changed, 81 insertions(+) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 38baf5fb8556..018596d80424 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -460,6 +460,16 @@ config SPLIT_LOCK_AC 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/split_lock/trigger_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/split_lock.c b/arch/x86/kernel/cpu/split_lock.c index 948a7fa948a2..eef69283aa5d 100644 --- a/arch/x86/kernel/cpu/split_lock.c +++ b/arch/x86/kernel/cpu/split_lock.c @@ -490,10 +490,81 @@ bios_store(struct kobject *kobj, struct kobj_attribute *attr, static struct kobj_attribute split_lock_ac_bios_enable = __ATTR_RW(bios); +#ifdef CONFIG_SPLIT_LOCK_AC_TEST +/* Execute locked cmpxchg with split locked address. */ +static void split_lock_test_kernel(void) +{ + char cptr[128] __aligned(64); + int *iptr, a = 10, b = 11; + + /* Increment the pointer, making it misaligned */ + iptr = (int *)(cptr + 61); + + /* Initial value 1 in iptr */ + *iptr = 1; + + pr_info("split lock test: misaligned address=%lx\n", + (unsigned long)iptr); + /* + * Since eax is equal to *iptr, the instruction loads value in b + * (i.e. 11) into iptr. If the instruction is executed correctly, + * the content of *iptr is changed to 11 from previous value 1. + * + * Accessing iptr cross two cache lines will trigger #AC in hardware. + * The instruction is re-executed during split lock is disabled and + * re-enabled later. + */ + asm volatile ("movl %1, %%eax\n\t" + "movl %1, %0\n\t" + "lock\n cmpxchgl %2, %0\n\t" + : "=m" (*iptr) + : "r"(a), "r"(b) + : "%eax"); + + if (*iptr == b) + pr_info("split lock kernel test passes\n"); + else + pr_info("split lock kernel test fails\n"); +} + +/* + * Writing 1 to /sys/kernel/split_lock/test_kernel triggers split locked + * access in kernel mode. + */ +static ssize_t +test_kernel_store(struct kobject *kobj, struct kobj_attribute *attr, + const char *buf, size_t count) +{ + u32 val; + int ret; + + if (split_lock_ac == DISABLE_SPLIT_LOCK_AC) + return -ENODEV; + + ret = kstrtou32(buf, 10, &val); + if (ret) + return ret; + + if (val != 1) + return -EINVAL; + + mutex_lock(&split_lock_mutex); + split_lock_test_kernel(); + mutex_unlock(&split_lock_mutex); + + return count; +} + +static struct kobj_attribute split_lock_ac_test = __ATTR_WO(test_kernel); +#endif /* CONFIG_SPLIT_LOCK_AC_TEST */ + static struct attribute *split_lock_attrs[] = { &split_lock_ac_enable.attr, &split_lock_ac_user.attr, &split_lock_ac_bios_enable.attr, +#ifdef CONFIG_SPLIT_LOCK_AC_TEST + &split_lock_ac_test.attr, +#endif NULL, }; -- 2.5.0
