@@ -95,6 +95,33 @@ static const char *usermode_action[] = {
"signal+warn"
};
+/* Return true if and only if the ARMv6 unaligned access model is in use. */
+static bool cpu_is_v6_unaligned(void)
+{
+ return cpu_architecture() >= CPU_ARCH_ARMv6 && (cr_alignment & CR_U);
+}
+
+static int safe_usermode(int new_usermode, bool warn)
+{
+ /*
+ * ARMv6 and later CPUs can perform unaligned accesses for
+ * most single load and store instructions up to word size.
+ * LDM, STM, LDRD and STRD still need to be handled.
+ *
+ * Ignoring the alignment fault is not an option on these
+ * CPUs since we spin re-faulting the instruction without
+ * making any progress.
+ */
+ if (cpu_is_v6_unaligned() && !(new_usermode & (UM_FIXUP | UM_SIGNAL))) {
+ new_usermode |= UM_FIXUP;
+
+ if (warn)
+ printk(KERN_WARNING "alignment: ignoring faults is unsafe on this CPU. Defaulting to fixup mode.\n");
+ }
+
+ return new_usermode;
+}
+
static int alignment_proc_show(struct seq_file *m, void *v)
{
seq_printf(m, "User:\t\t%lu\n", ai_user);
@@ -125,7 +152,7 @@ static ssize_t alignment_proc_write(struct file *file, const char __user *buffer
if (get_user(mode, buffer))
return -EFAULT;
if (mode >= '0' && mode <= '5')
- ai_usermode = mode - '0';
+ ai_usermode = safe_usermode(mode - '0', true)
}
return count;
}
@@ -923,20 +950,11 @@ static int __init alignment_init(void)
return -ENOMEM;
#endif
- /*
- * ARMv6 and later CPUs can perform unaligned accesses for
- * most single load and store instructions up to word size.
- * LDM, STM, LDRD and STRD still need to be handled.
- *
- * Ignoring the alignment fault is not an option on these
- * CPUs since we spin re-faulting the instruction without
- * making any progress.
- */
- if (cpu_architecture() >= CPU_ARCH_ARMv6 && (cr_alignment & CR_U)) {
+ if (cpu_is_v6_unaligned()) {
cr_alignment &= ~CR_A;
cr_no_alignment &= ~CR_A;
set_cr(cr_alignment);
- ai_usermode = UM_FIXUP;
+ ai_usermode = safe_usermode(ai_usermode, false);
}
hook_fault_code(1, do_alignment, SIGBUS, BUS_ADRALN,
Currently, it's possible to set the kernel to ignore alignment faults when changing the alignment fault handling mode at runtime via /proc/sys/alignment, even though this is undesirable on ARMv6 and above, where it can result in infinite spins where an un-fixed- up instruction repeatedly faults. In addition, the kernel clobbers any alignment mode specified on the command-line if running on ARMv6 or above. This patch factors out the necessary safety check into a couple of new helper functions, and checks and modifies the fault handling mode as appropriate on boot and on writes to /proc/cpu/alignment. Prior to ARMv6, the behaviour is unchanged. For ARMv6 and above, the behaviour changes as follows: * Attempting to ignore faults on ARMv6 results in the mode being forced to UM_FIXUP instead. A warning is printed if this happened as a result of a write to /proc/cpu/alignment. The user's UM_WARN bit (if present) is still honoured. * An alignment= argument from the kernel command-line is now honoured, except that the kernel will modify the specified mode as described above. This is allows modes such as UM_SIGNAL and UM_WARN to be active immediately from boot, which is useful for debugging purposes. Signed-off-by: Dave Martin <dave.martin@linaro.org> --- arch/arm/mm/alignment.c | 42 ++++++++++++++++++++++++++++++------------ 1 files changed, 30 insertions(+), 12 deletions(-)