[PATCH v2] arc: Re-enable MMU upon die()

[Jose Abreu]

Oops, the commit title is now a little bit odd. Let me rephrase
and send a new version.

On 01-09-2017 17:00, Jose Abreu wrote:
> I recently came upon a scenario where I would get a double fault
> after a machine check error. It turns out that for Ksymbol lookup
> to work with modules we need to have MMU enabled because module
> address is mapped in the cached space.
>
> This patch re-enables the MMU before start printing the stacktrace
> making stacktracing of modules work upon a fatal exception.
>
> Signed-off-by: Jose Abreu <joabreu at synopsys.com>
> Cc: Vineet Gupta <vgupta at synopsys.com>
> Cc: Alexey Brodkin <abrodkin at synopsys.com>
>
> Changes from v1:
> 	- Moved MMU re-enable to machine check exception handler
> ---
>  arch/arc/kernel/traps.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/arch/arc/kernel/traps.c b/arch/arc/kernel/traps.c
> index ff83e78..d92f161 100644
> --- a/arch/arc/kernel/traps.c
> +++ b/arch/arc/kernel/traps.c
> @@ -19,6 +19,8 @@
>  #include <linux/ptrace.h>
>  #include <linux/kprobes.h>
>  #include <linux/kgdb.h>
> +#include <asm/arcregs.h>
> +#include <asm/mmu.h>
>  #include <asm/setup.h>
>  #include <asm/unaligned.h>
>  #include <asm/kprobes.h>
> @@ -103,6 +105,9 @@ int do_misaligned_access(unsigned long address, struct pt_regs *regs,
>   */
>  void do_machine_check_fault(unsigned long address, struct pt_regs *regs)
>  {
> +	/* MMU must be enabled for Ksymbol lookup in modules */
> +	write_aux_reg(ARC_REG_PID, MMU_ENABLE | read_aux_reg(ARC_REG_PID));
> +
>  	die("Machine Check Exception", regs, address);
>  }
>