On Thu, Jan 05, 2017 at 05:32:36PM +0000, Mark Rutland wrote:
> 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@xxxxxxx>
> Reported-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
> Cc: Russell King <linux@xxxxxxxxxxxxxxx>
> Cc: Stephen Boyd <sboyd@xxxxxxxxxxxxxx>
> Cc: Will Deacon <will.deacon@xxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> ---
> arch/arm/include/asm/cputype.h | 3 +++
> arch/arm/kernel/hw_breakpoint.c | 16 ++++++++++++++++
> 2 files changed, 19 insertions(+)
>
> diff --git a/arch/arm/include/asm/cputype.h b/arch/arm/include/asm/cputype.h
> index 522b5fe..b62eaeb 100644
> --- a/arch/arm/include/asm/cputype.h
> +++ b/arch/arm/include/asm/cputype.h
> @@ -94,6 +94,9 @@
> #define ARM_CPU_XSCALE_ARCH_V2 0x4000
> #define ARM_CPU_XSCALE_ARCH_V3 0x6000
>
> +/* 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 188180b..5d68ff9 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. Breakpoints and watchpoints disabled\n");
nit: we're disabling *hardware* breakpoints and watchpoints, so it's worth
mentioning that in the print.
With that:
Acked-by: Will Deacon <will.deacon@xxxxxxx>
Please put this into Russell's patch system.
Will
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