Re: [RFC][PATCH v2] Controlling kexec behaviour when hardware error happened.

[Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>]

(2011/02/10 18:14), Borislav Petkov wrote:
> On Thu, Feb 10, 2011 at 05:36:58PM +0900, Hidetoshi Seto wrote:
>> (2011/02/10 1:35), Seiji Aguchi wrote:
> 
> [..]
> 
>>> diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
>>> index d916183..e76b47b 100644
>>> --- a/arch/x86/kernel/cpu/mcheck/mce.c
>>> +++ b/arch/x86/kernel/cpu/mcheck/mce.c
>>> @@ -944,6 +944,8 @@ void do_machine_check(struct pt_regs *regs, long error_code)
>>>  
>>>  	percpu_inc(mce_exception_count);
>>>  
>>> +	hwerr_flag = 1;
>>> +
>>>  	if (notify_die(DIE_NMI, "machine check", regs, error_code,
>>>  			   18, SIGKILL) == NOTIFY_STOP)
>>>  		goto out;
>>
>> Now x86 supports some recoverable machine check, so setting
>> flag here will prevent running kexec on systems that have
>> encountered such recoverable machine check and recovered.
>>
>> I think mce_panic() is proper place to set this flag "hwerr_flag".
> 
> I agree, in that case it is unsafe to run kexec only after the error
> cannot be recovered by software.
> 
> Also, hwerr_flag is really a bad naming choice, how about
> "hwerr_unrecoverable" or "hw_compromised" or "recovery_futile" or
> "hw_incurable" or simply say what happened: "pcc" = processor context
> corrupt (and a reliable restarting might not be possible). This could be
> used by others too, besides kexec.

Or how about something like hwerr_panic() to clear that the panic is
requested due to hardware error.

Anyway, Aguchi-san, please note that we should not turn off kexec before
encountering fatal hardware error and before printing/transmitting
enough hardware error log to out of this system.

> 
> [..]
> 
>>> diff --git a/mm/memory-failure.c b/mm/memory-failure.c index 0207c2f..0178f47 100644
>>> --- a/mm/memory-failure.c
>>> +++ b/mm/memory-failure.c
>>> @@ -994,6 +994,8 @@ int __memory_failure(unsigned long pfn, int trapno, int flags)
>>>  	int res;
>>>  	unsigned int nr_pages;
>>>  
>>> +	hwerr_flag = 1;
>>> +
>>>  	if (!sysctl_memory_failure_recovery)
>>>  		panic("Memory failure from trap %d on page %lx", trapno, pfn);
>>>  
>>
>> For similar reason, setting flag here is not good for
>> systems working after isolating some poisoned memory page.
>>
>> Why not:
>>  if (!sysctl_memory_failure_recovery) {
>>  	hwerr_flag = 1;
>>  	panic("Memory failure from trap %d on page %lx", trapno, pfn);
>>  }
> 
> Why do we need that in memory-failure.c at all? I mean, when we consume
> the UC, we'll end up in mce_panic() anyway.

One possible answer is that memory-failure.c is not x86 specific.


Thanks,
H.Seto