ARM: 8634/1: hw_breakpoint: blacklist Scorpion CPUs

commit ddc37832a1349f474c4532de381498020ed71d31 upstream.

On APQ8060, the kernel crashes in arch_hw_breakpoint_init, taking an
undefined instruction trap within write_wb_reg. This is because Scorpion
CPUs erroneously appear to set DBGPRSR.SPD when WFI is issued, even if
the core is not powered down. When DBGPRSR.SPD is set, breakpoint and
watchpoint registers are treated as undefined.

It's possible to trigger similar crashes later on from userspace, by
requesting the kernel to install a breakpoint or watchpoint, as we can
go idle at any point between the reset of the debug registers and their
later use. This has always been the case.

Given that this has always been broken, no-one has complained until now,
and there is no clear workaround, disable hardware breakpoints and
watchpoints on Scorpion to avoid these issues.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reported-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Acked-by: Will Deacon <will.deacon@arm.com>
Cc: Russell King <linux@armlinux.org.uk>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
[bwh: Backported to 3.2:
 - Open-code read_cpuid_part()
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/arch/arm/include/asm/cputype.h b/arch/arm/include/asm/cputype.h
index cb47d28cbe1f81c4cfb43de4d1f08dbcec9f0cf7..a6f926be910f1e72232c4187b3b6893f17afeb2c 100644 (file)
--- a/arch/arm/include/asm/cputype.h
+++ b/arch/arm/include/asm/cputype.h
@@ -25,6 +25,9 @@
 #define CPUID_EXT_ISAR4        "c2, 4"
 #define CPUID_EXT_ISAR5        "c2, 5"
 
+/* Qualcomm implemented cores */
+#define ARM_CPU_PART_SCORPION          0x510002d0
+
 extern unsigned int processor_id;
 
 #ifdef CONFIG_CPU_CP15

diff --git a/arch/arm/kernel/hw_breakpoint.c b/arch/arm/kernel/hw_breakpoint.c
index 2bc1a8e923056c8f2a25ca3c60060a99c6583efd..bdafb83cd52e66d8e621f4eb01949d16941e144d 100644 (file)
--- a/arch/arm/kernel/hw_breakpoint.c
+++ b/arch/arm/kernel/hw_breakpoint.c
@@ -1001,6 +1001,22 @@ static int __init arch_hw_breakpoint_init(void)
                return 0;
        }
 
+       /*
+        * Scorpion CPUs (at least those in APQ8060) seem to set DBGPRSR.SPD
+        * whenever a WFI is issued, even if the core is not powered down, in
+        * violation of the architecture.  When DBGPRSR.SPD is set, accesses to
+        * breakpoint and watchpoint registers are treated as undefined, so
+        * this results in boot time and runtime failures when these are
+        * accessed and we unexpectedly take a trap.
+        *
+        * It's not clear if/how this can be worked around, so we blacklist
+        * Scorpion CPUs to avoid these issues.
+       */
+       if ((read_cpuid_id() & 0xff00fff0) == ARM_CPU_PART_SCORPION) {
+               pr_info("Scorpion CPU detected. Hardware breakpoints and watchpoints disabled\n");
+               return 0;
+       }
+
        /* Determine how many BRPs/WRPs are available. */
        core_num_brps = get_num_brps();
        core_num_wrps = get_num_wrps();