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

[Baicar, Tyler]

Hi Will,

On 1/4/2017 6:54 AM, Will Deacon wrote:
> 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@xxxxxxxxxxxxxx>
> > Signed-off-by: Jonathan (Zhixiong) Zhang <zjzhang@xxxxxxxxxxxxxx>
> > Signed-off-by: Naveen Kaje <nkaje@xxxxxxxxxxxxxx>
> > ---
> >   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.
I originally used the acronym and got feedback to expand it, but I'll 
revert back to just using the acronym.
Using a notifier here is consistent with the SCI error type in the GHES 
code which is also only registered in
the GHES code. I can remove the notifier for SEA if you think making the 
call directly is better here.
> >   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".
I will expand this in the next patchset.
> > +	{ 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".
I will add them back in the next patchset.

Thanks,
Tyler
> Will

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