From ddc37832a1349f474c4532de381498020ed71d31 Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Fri, 6 Jan 2017 13:12:47 +0100 Subject: ARM: 8634/1: hw_breakpoint: blacklist Scorpion CPUs 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 Reported-by: Linus Walleij Reviewed-by: Stephen Boyd Acked-by: Will Deacon Cc: Russell King Cc: stable@vger.kernel.org Signed-off-by: Russell King --- arch/arm/kernel/hw_breakpoint.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) (limited to 'arch/arm/kernel') diff --git a/arch/arm/kernel/hw_breakpoint.c b/arch/arm/kernel/hw_breakpoint.c index 188180b5523d..be3b3fbd382f 100644 --- a/arch/arm/kernel/hw_breakpoint.c +++ b/arch/arm/kernel/hw_breakpoint.c @@ -1063,6 +1063,22 @@ 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_part() == ARM_CPU_PART_SCORPION) { + pr_info("Scorpion CPU detected. Hardware breakpoints and watchpoints disabled\n"); + return 0; + } + has_ossr = core_has_os_save_restore(); /* Determine how many BRPs/WRPs are available. */ -- cgit v1.2.3