On Friday 16 August 2013 01:34 PM, Mahesh J Salgaonkar wrote:
> From: Mahesh Salgaonkar <mah...@linux.vnet.ibm.com>
>
> This patch introduces exclusive emergency stack for machine check exception.
> We use emergency stack to handle machine check exception so that we can save
> MCE information (srr1, srr0, dar and dsisr) before turning on ME bit and be
> ready for re-entrancy. This helps us to prevent clobbering of MCE information
> in case of nested machine checks.
>
> The reason for using emergency stack over normal kernel stack is that the
> machine check might occur in the middle of setting up a stack frame which may
> result into improper use of kernel stack.
>
> Signed-off-by: Mahesh Salgaonkar <mah...@linux.vnet.ibm.com>
> ---
> arch/powerpc/include/asm/paca.h | 9 +++++++++
> arch/powerpc/kernel/setup_64.c | 8 +++++++-
> arch/powerpc/xmon/xmon.c | 2 ++
> 3 files changed, 18 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/include/asm/paca.h b/arch/powerpc/include/asm/paca.h
> index 77c91e7..b4ca4e9 100644
> --- a/arch/powerpc/include/asm/paca.h
> +++ b/arch/powerpc/include/asm/paca.h
> @@ -147,6 +147,15 @@ struct paca_struct {
> */
> struct opal_machine_check_event *opal_mc_evt;
> #endif
> +#ifdef CONFIG_PPC_BOOK3S_64
> + /* Exclusive emergency stack pointer for machine check exception. */
> + void *mc_emergency_sp;
> + /*
> + * Flag to check whether we are in machine check early handler
> + * and already using emergency stack.
> + */
> + u16 in_mce;
> +#endif
>
> /* Stuff for accurate time accounting */
> u64 user_time; /* accumulated usermode TB ticks */
> diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
> index 389fb807..3fdbdb0 100644
> --- a/arch/powerpc/kernel/setup_64.c
> +++ b/arch/powerpc/kernel/setup_64.c
> @@ -529,7 +529,8 @@ static void __init exc_lvl_early_init(void)
>
> /*
> * Stack space used when we detect a bad kernel stack pointer, and
> - * early in SMP boots before relocation is enabled.
> + * early in SMP boots before relocation is enabled. Exclusive emergency
> + * stack for machine checks.
> */
> static void __init emergency_stack_init(void)
> {
> @@ -552,6 +553,11 @@ static void __init emergency_stack_init(void)
> sp = memblock_alloc_base(THREAD_SIZE, THREAD_SIZE, limit);
> sp += THREAD_SIZE;
> paca[i].emergency_sp = __va(sp);
> +
> + /* emergency stack for machine check exception handling. */
> + sp = memblock_alloc_base(THREAD_SIZE, THREAD_SIZE, limit);
> + sp += THREAD_SIZE;
> + paca[i].mc_emergency_sp = __va(sp);
> }
> }
>
Just a concern, kindly ignore it if it is irrelevant.
you have defined mc_emergency_sp under CONFIG_PPC_BOOK3S_64, but
assigning memory in a common code. This may break build for other
configs such as like ppc64e_defconfig.
> diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
> index 96bf5bd..147a5e98 100644
> --- a/arch/powerpc/xmon/xmon.c
> +++ b/arch/powerpc/xmon/xmon.c
> @@ -2044,6 +2044,8 @@ static void dump_one_paca(int cpu)
> DUMP(p, stab_addr, "lx");
> #endif
> DUMP(p, emergency_sp, "p");
> + DUMP(p, mc_emergency_sp, "p");
> + DUMP(p, in_mce, "x");
> DUMP(p, data_offset, "lx");
> DUMP(p, hw_cpu_id, "x");
> DUMP(p, cpu_start, "x");
>
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