linux-kernel - Re: [PATCH 5/6] x86, mce: handle "action required" errors

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Date:	Wed, 14 Dec 2011 17:04:10 +0100
From:	Borislav Petkov <bp@...64.org>
To:	Tony Luck <tony.luck@...el.com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	"Huang, Ying" <ying.huang@...el.com>,
	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
Subject: Re: [PATCH 5/6] x86, mce: handle "action required" errors

On Mon, Dec 12, 2011 at 01:47:45PM -0800, Tony Luck wrote:
[..]

> - * Called after mce notification in process context. This code
> - * is allowed to sleep. Call the high level VM handler to process
> - * any corrupted pages.
> - * Assume that the work queue code only calls this one at a time
> - * per CPU.
> - * Note we don't disable preemption, so this code might run on the wrong
> - * CPU. In this case the event is picked up by the scheduled work queue.
> - * This is merely a fast path to expedite processing in some common
> - * cases.
> + * Called in process context that interrupted by MCE and marked with
> + * TIF_MCE_NOTFY, just before returning to errorneous userland.
> + * This code is allowed to sleep.
> + * Attempt possible recovery such as calling the high level VM handler to
> + * process any corrupted pages, and kill/signal current process if required.
>   */
>  void mce_notify_process(void)
>  {
> +	__u64	paddr = paddr;
>  	unsigned long pfn;
> -	mce_notify_irq();
> -	while (mce_ring_get(&pfn))
> -		memory_failure(pfn, MCE_VECTOR, 0);
> +
> +	if (!mce_find_info(&paddr))
> +		mce_panic("Lost address", NULL, NULL);

Wouldn't it be good to return struct mce_info *mi here in addition to
&paddr...

> +	pfn = paddr >> PAGE_SHIFT;
> +
> +	clear_thread_flag(TIF_MCE_NOTIFY);
> +
> +	pr_err("Uncorrected hardware memory error in user-access at %llx",
> +		 paddr);
> +	if (memory_failure(pfn, MCE_VECTOR, MF_ACTION_REQUIRED) < 0) {
> +		pr_err("Memory error not recovered");
> +		force_sig(SIGBUS, current);
> +	} else {
> +		pr_err("Memory error recovered");
> +		mce_clear_info();

so that you don't need to iterate again over the mce_info array but do:

	mce_clear_info(mi);

?

This assumes, of course, that you have only one AR MCE per task, per
return to userspace. I guess this is fine for now.

> +	}
>  }
>  
>  static void mce_process_work(struct work_struct *dummy)
>  {
> -	mce_notify_process();
> +	unsigned long pfn;
> +
> +	while (mce_ring_get(&pfn))
> +		memory_failure(pfn, MCE_VECTOR, 0);
>  }
>  
>  #ifdef CONFIG_X86_MCE_INTEL
> @@ -1232,8 +1246,6 @@ int mce_notify_irq(void)
>  	/* Not more than two messages every minute */
>  	static DEFINE_RATELIMIT_STATE(ratelimit, 60*HZ, 2);
>  
> -	clear_thread_flag(TIF_MCE_NOTIFY);
> -
>  	if (test_and_clear_bit(0, &mce_need_notify)) {
>  		/* wake processes polling /dev/mcelog */
>  		wake_up_interruptible(&mce_chrdev_wait);
> -- 
> 1.7.3.1
> 

Thanks.

-- 
Regards/Gruss,
Boris.

Advanced Micro Devices GmbH
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