ARM: hw_breakpoint: fix ordering of debug register reset sequence

The debug register reset sequence for v7 and v7.1 is congruent with
tap-dancing through a minefield.

Rather than wait until we've blown ourselves to pieces, this patch
instead checks the debug_err_mask after each potentially faulting
operation. We also move the enabling of monitor_mode to the end of the
sequence in order to prevent spurious debug events generated by UNKNOWN
register values.

Signed-off-by: Will Deacon <will.deacon@arm.com>

diff --git a/arch/arm/kernel/hw_breakpoint.c b/arch/arm/kernel/hw_breakpoint.c
index 169dcce83d1326f801d9ec5ebb6e6c1424942980..e76cf1a951462838ce1e7364243ea0be21ab798e 100644 (file)
--- a/arch/arm/kernel/hw_breakpoint.c
+++ b/arch/arm/kernel/hw_breakpoint.c
@@ -231,8 +231,6 @@ static int get_num_brps(void)
 static int enable_monitor_mode(void)
 {
        u32 dscr;
-       int ret = 0;
-
        ARM_DBG_READ(c1, 0, dscr);
 
        /* If monitor mode is already enabled, just return. */
@@ -251,17 +249,18 @@ static int enable_monitor_mode(void)
                isb();
                break;
        default:
-               ret = -ENODEV;
-               goto out;
+               return -ENODEV;
        }
 
        /* Check that the write made it through. */
        ARM_DBG_READ(c1, 0, dscr);
-       if (!(dscr & ARM_DSCR_MDBGEN))
-               ret = -EPERM;
+       if (WARN_ONCE(!(dscr & ARM_DSCR_MDBGEN),
+               "Failed to enable monitor mode on CPU %d.\n",
+               smp_processor_id()))
+               return -EPERM;
 
 out:
-       return ret;
+       return 0;
 }
 
 int hw_breakpoint_slots(int type)
@@ -962,11 +961,16 @@ clear_vcr:
        asm volatile("mcr p14, 0, %0, c0, c7, 0" : : "r" (0));
        isb();
 
-reset_regs:
-       if (enable_monitor_mode())
+       if (cpumask_intersects(&debug_err_mask, cpumask_of(cpu))) {
+               pr_warning("CPU %d failed to disable vector catch\n", cpu);
                return;
+       }
 
-       /* We must also reset any reserved registers. */
+reset_regs:
+       /*
+        * The control/value register pairs are UNKNOWN out of reset so
+        * clear them to avoid spurious debug events.
+        */
        raw_num_brps = get_num_brp_resources();
        for (i = 0; i < raw_num_brps; ++i) {
                write_wb_reg(ARM_BASE_BCR + i, 0UL);
@@ -977,6 +981,18 @@ reset_regs:
                write_wb_reg(ARM_BASE_WCR + i, 0UL);
                write_wb_reg(ARM_BASE_WVR + i, 0UL);
        }
+
+       if (cpumask_intersects(&debug_err_mask, cpumask_of(cpu))) {
+               pr_warning("CPU %d failed to clear debug register pairs\n", cpu);
+               return;
+       }
+
+       /*
+        * Have a crack at enabling monitor mode. We don't actually need
+        * it yet, but reporting an error early is useful if it fails.
+        */
+       if (enable_monitor_mode())
+               cpumask_or(&debug_err_mask, &debug_err_mask, cpumask_of(cpu));
 }
 
 static int __cpuinit dbg_reset_notify(struct notifier_block *self,