Re: [PATCH V6 04/10] arm64: exception: handle Synchronous External Abort

[Will Deacon <will.deacon@arm.com>]

On Wed, Dec 07, 2016 at 02:48:17PM -0700, Tyler Baicar wrote:
> SEA exceptions are often caused by an uncorrected hardware
> error, and are handled when data abort and instruction abort
> exception classes have specific values for their Fault Status
> Code.
> When SEA occurs, before killing the process, go through
> the handlers registered in the notification list.
> Update fault_info[] with specific SEA faults so that the
> new SEA handler is used.
> 
> Signed-off-by: Tyler Baicar <tbaicar@codeaurora.org>
> Signed-off-by: Jonathan (Zhixiong) Zhang <zjzhang@codeaurora.org>
> Signed-off-by: Naveen Kaje <nkaje@codeaurora.org>
> ---
>  arch/arm64/include/asm/system_misc.h | 13 ++++++++
>  arch/arm64/mm/fault.c                | 58 +++++++++++++++++++++++++++++-------
>  2 files changed, 61 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/system_misc.h b/arch/arm64/include/asm/system_misc.h
> index 57f110b..9040e1d 100644
> --- a/arch/arm64/include/asm/system_misc.h
> +++ b/arch/arm64/include/asm/system_misc.h
> @@ -64,4 +64,17 @@ extern void (*arm_pm_restart)(enum reboot_mode reboot_mode, const char *cmd);
>  
>  #endif	/* __ASSEMBLY__ */
>  
> +/*
> + * The functions below are used to register and unregister callbacks
> + * that are to be invoked when a Synchronous External Abort (SEA)
> + * occurs. An SEA is raised by certain fault status codes that have
> + * either data or instruction abort as the exception class, and
> + * callbacks may be registered to parse or handle such hardware errors.
> + *
> + * Registered callbacks are run in an interrupt/atomic context. They
> + * are not allowed to block or sleep.
> + */
> +int register_synchronous_ext_abort_notifier(struct notifier_block *nb);
> +void unregister_synchronous_ext_abort_notifier(struct notifier_block *nb);

I think that we may as well use the "SEA" acronym consistently in code,
expanding it only for strings and comments, so these can be renamed to
{register,unregister}_sea_notifier. That said, what is the use of having a
notifier chain here as well as in the ghes code? If the ghes code is the
only place to register a notifier, we may as well start simple and call that
code directly, like we call handle_mm_fault directly for data aborts.

>  static const struct fault_info {
>  	int	(*fn)(unsigned long addr, unsigned int esr, struct pt_regs *regs);
>  	int	sig;
> @@ -502,22 +540,22 @@ static const struct fault_info {
>  	{ do_page_fault,	SIGSEGV, SEGV_ACCERR,	"level 1 permission fault"	},
>  	{ do_page_fault,	SIGSEGV, SEGV_ACCERR,	"level 2 permission fault"	},
>  	{ do_page_fault,	SIGSEGV, SEGV_ACCERR,	"level 3 permission fault"	},
> -	{ do_bad,		SIGBUS,  0,		"synchronous external abort"	},
> +	{ do_synch_ext_abort,	SIGBUS,  0,		"synchronous external abort"	},

Again, just stick with do_sea for the function name...

>  	{ do_bad,		SIGBUS,  0,		"unknown 17"			},
>  	{ do_bad,		SIGBUS,  0,		"unknown 18"			},
>  	{ do_bad,		SIGBUS,  0,		"unknown 19"			},
> -	{ do_bad,		SIGBUS,  0,		"synchronous abort (translation table walk)" },
> -	{ do_bad,		SIGBUS,  0,		"synchronous abort (translation table walk)" },
> -	{ do_bad,		SIGBUS,  0,		"synchronous abort (translation table walk)" },
> -	{ do_bad,		SIGBUS,  0,		"synchronous abort (translation table walk)" },
> -	{ do_bad,		SIGBUS,  0,		"synchronous parity error"	},
> +	{ do_synch_ext_abort,	SIGBUS,  0,		"level 0 SEA (trans tbl walk)"	},

... but there's no need to abbreviate "translation table walk" here. Long
strings that run over 80 chars are fine. Similarly for "SEA".

> +	{ do_synch_ext_abort,	SIGBUS,  0,		"level 1 SEA (trans tbl walk)"	},
> +	{ do_synch_ext_abort,	SIGBUS,  0,		"level 2 SEA (trans tbl walk)"	},
> +	{ do_synch_ext_abort,	SIGBUS,  0,		"level 3 SEA (trans tbl walk)"	},
> +	{ do_synch_ext_abort,	SIGBUS,  0,		"synchronous parity or ECC err" },
>  	{ do_bad,		SIGBUS,  0,		"unknown 25"			},
>  	{ do_bad,		SIGBUS,  0,		"unknown 26"			},
>  	{ do_bad,		SIGBUS,  0,		"unknown 27"			},
> -	{ do_bad,		SIGBUS,  0,		"synchronous parity error (translation table walk)" },
> -	{ do_bad,		SIGBUS,  0,		"synchronous parity error (translation table walk)" },
> -	{ do_bad,		SIGBUS,  0,		"synchronous parity error (translation table walk)" },
> -	{ do_bad,		SIGBUS,  0,		"synchronous parity error (translation table walk)" },
> +	{ do_synch_ext_abort,	SIGBUS,  0,		"level 0 synch parity error"	},
> +	{ do_synch_ext_abort,	SIGBUS,  0,		"level 1 synch parity error"	},
> +	{ do_synch_ext_abort,	SIGBUS,  0,		"level 2 synch parity error"	},
> +	{ do_synch_ext_abort,	SIGBUS,  0,		"level 3 synch parity error"	},

Please keep mention of "translation table walk", since we have exception
levels too and it's confusing just saying "level n".

Will