linux-kernel - Re: [PATCH V7 04/10] arm64: exception: handle Synchronous External Abort

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Message-ID: <9185f5f2-7bc4-5727-af3a-920dd22578dc@codeaurora.org>
Date:   Wed, 18 Jan 2017 15:52:03 -0700
From:   "Baicar, Tyler" <tbaicar@...eaurora.org>
To:     James Morse <james.morse@....com>
Cc:     Will Deacon <will.deacon@....com>, christoffer.dall@...aro.org,
        marc.zyngier@....com, pbonzini@...hat.com, rkrcmar@...hat.com,
        linux@...linux.org.uk, catalin.marinas@....com, rjw@...ysocki.net,
        lenb@...nel.org, matt@...eblueprint.co.uk, robert.moore@...el.com,
        lv.zheng@...el.com, nkaje@...eaurora.org, zjzhang@...eaurora.org,
        mark.rutland@....com, akpm@...ux-foundation.org,
        eun.taik.lee@...sung.com, sandeepa.s.prabhu@...il.com,
        labbott@...hat.com, shijie.huang@....com, rruigrok@...eaurora.org,
        paul.gortmaker@...driver.com, tn@...ihalf.com, fu.wei@...aro.org,
        rostedt@...dmis.org, bristot@...hat.com,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-acpi@...r.kernel.org, linux-efi@...r.kernel.org,
        devel@...ica.org, Suzuki.Poulose@....com, punit.agrawal@....com,
        astone@...hat.com, harba@...eaurora.org, hanjun.guo@...aro.org,
        john.garry@...wei.com, shiju.jose@...wei.com
Subject: Re: [PATCH V7 04/10] arm64: exception: handle Synchronous External
 Abort

On 1/17/2017 3:23 AM, James Morse wrote:
> Hi Tyler,
>
> On 16/01/17 11:53, Will Deacon wrote:
>> On Thu, Jan 12, 2017 at 11:15:18AM -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.
>>> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
>>> index 05d2bd7..81039c7 100644
>>> --- a/arch/arm64/mm/fault.c
>>> +++ b/arch/arm64/mm/fault.c
>>> @@ -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 (translation table walk)"	},
>>> +	{ do_sea,		SIGBUS,  0,		"level 1 SEA (translation table walk)"	},
>>> +	{ do_sea,		SIGBUS,  0,		"level 2 SEA (translation table walk)"	},
>>> +	{ do_sea,		SIGBUS,  0,		"level 3 SEA (translation table walk)"	},
>> Perhaps I wasn't clear enough in my previous review, but please expand the
>> acronym for strings and comments.
>
> The 'SEA' in this user-string doesn't add anything. Now that these use do_sea()
> instead of do_bad(), when they are printed won't it be:
>> Synchronous External Abort: level 3 SEA (translation table walk) (...) at ....

Good point, yes they will:

+	pr_err("Synchronous External Abort: %s (0x%08x) at 0x%016lx\n",
+		 fault_name(esr), esr, addr);

I can just remove SEA here then.

Thanks,
Tyler


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