Re: [PATCH V3 04/10] arm64: exception: handle Synchronous External Abort

[Baicar, Tyler]

Hello Punit,

On 10/12/2016 11:46 AM, Punit Agrawal wrote:
> Hi Tyler,
>
> A couple of hopefully not bike shedding comments below.
>
> Tyler Baicar <tbaicar@xxxxxxxxxxxxxx> writes:
>
> > 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: Jonathan (Zhixiong) Zhang <zjzhang@xxxxxxxxxxxxxx>
> > Signed-off-by: Tyler Baicar <tbaicar@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..90daf4a 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 sea_register_handler_chain(struct notifier_block *nb);
> > +void sea_unregister_handler_chain(struct notifier_block *nb);
> > +
> >   #endif	/* __ASM_SYSTEM_MISC_H */
> > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> > index 05d2bd7..81cb7ad 100644
> > --- a/arch/arm64/mm/fault.c
> > +++ b/arch/arm64/mm/fault.c
> > @@ -39,6 +39,22 @@
> >   #include <asm/pgtable.h>
> >   #include <asm/tlbflush.h>
> >   
> > +/*
> > + * GHES SEA handler code may register a notifier call here to
> > + * handle HW error record passed from platform.
> > + */
> > +static ATOMIC_NOTIFIER_HEAD(sea_handler_chain);
> > +
> > +int sea_register_handler_chain(struct notifier_block *nb)
> > +{
> > +	return atomic_notifier_chain_register(&sea_handler_chain, nb);
> > +}
> > +
> > +void sea_unregister_handler_chain(struct notifier_block *nb)
> > +{
> > +	atomic_notifier_chain_unregister(&sea_handler_chain, nb);
> > +}
> > +
> What do you think of naming the above functions as
> [un]register_synchonous_ext_abort_notifier?
>
> For an API, I find "sea" doesn't quite convey the message.
>
> One more comment below.
Yes, those names seem easier to understand.
> >   static const char *fault_name(unsigned int esr);
> >   
> >   #ifdef CONFIG_KPROBES
> > @@ -480,6 +496,28 @@ static int do_bad(unsigned long addr, unsigned int esr, struct pt_regs *regs)
> >   	return 1;
> >   }
> >   
> > +/*
> > + * This abort handler deals with Synchronous External Abort.
> > + * It calls notifiers, and then returns "fault".
> > + */
> > +static int do_sea(unsigned long addr, unsigned int esr, struct pt_regs *regs)
> > +{
> > +	struct siginfo info;
> > +
> > +	atomic_notifier_call_chain(&sea_handler_chain, 0, NULL);
> > +
> > +	pr_err("Synchronous External Abort: %s (0x%08x) at 0x%016lx\n",
> > +		 fault_name(esr), esr, addr);
> > +
> > +	info.si_signo = SIGBUS;
> > +	info.si_errno = 0;
> > +	info.si_code  = 0;
> > +	info.si_addr  = (void __user *)addr;
> > +	arm64_notify_die("", regs, &info, esr);
> > +
> > +	return 0;
> > +}
> > +
> >   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_sea,		SIGBUS,  0,		"synchronous external abort"	},
> >   	{ 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_sea,		SIGBUS,  0,		"level 0 SEA (trans tbl walk)"	},
> > +	{ do_sea,		SIGBUS,  0,		"level 1 SEA (trans tbl walk)"	},
> > +	{ do_sea,		SIGBUS,  0,		"level 2 SEA (trans tbl walk)"	},
> > +	{ do_sea,		SIGBUS,  0,		"level 3 SEA (trans tbl walk)"	},
>                                                                   ^^^
> The comment about naming applies here as well.
>
> Thanks,
> Punit
I'll expand sea here as well. This should make it easier to understand 
without knowing the code.

Thanks,
Tyler
> [...]

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