Re: [PATCH v2] hw/poison: Add in-use hugepage filter judgement and avoid filter page impact on mce handler

["HORIGUCHI NAOYA(堀口 直也)" <naoya.horiguchi@nec.com>]

On Wed, Feb 16, 2022 at 10:00:38PM -0500, luofei wrote:
> After successfully obtaining the reference count of the huge
> page, it is still necessary to call hwpoison_filter() to make a
> filter judgement, otherwise the filter hugepage will be unmaped
> and the related process may be killed.
> 
> Also when the huge page meets the filter conditions, it should
> not be regarded as successful memory_failure() processing for
> mce handler, but should return a value to inform the caller,
> otherwise the caller regards the error page has been identified
> and isolated, which may lead to calling set_mce_nospec() to change
> page attribute, etc.
> 
> Signed-off-by: luofei <luofei@unicloud.com>

This patch seems to do two separate things (introducing MF_MCE_HANDLE,
and adding hwpoison_filter() in memory_failure_hugetlb()), so could you
separate the patch into two?

> ---
>  arch/x86/kernel/cpu/mce/core.c | 22 +++++++++++-----------
>  include/linux/mm.h             |  1 +
>  mm/memory-failure.c            | 25 +++++++++++++++++++++++--
>  3 files changed, 35 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
> index 5818b837fd4d..c2b99c60225f 100644
> --- a/arch/x86/kernel/cpu/mce/core.c
> +++ b/arch/x86/kernel/cpu/mce/core.c
> @@ -612,7 +612,7 @@ static int uc_decode_notifier(struct notifier_block *nb, unsigned long val,
>  		return NOTIFY_DONE;
>  
>  	pfn = mce->addr >> PAGE_SHIFT;
> -	if (!memory_failure(pfn, 0)) {
> +	if (!memory_failure(pfn, MF_MCE_HANDLE)) {
>  		set_mce_nospec(pfn, whole_page(mce));
>  		mce->kflags |= MCE_HANDLED_UC;
>  	}
> @@ -1286,7 +1286,7 @@ static void kill_me_now(struct callback_head *ch)
>  static void kill_me_maybe(struct callback_head *cb)
>  {
>  	struct task_struct *p = container_of(cb, struct task_struct, mce_kill_me);
> -	int flags = MF_ACTION_REQUIRED;
> +	int flags = MF_ACTION_REQUIRED | MF_MCE_HANDLE;
>  	int ret;
>  
>  	p->mce_count = 0;
> @@ -1300,14 +1300,14 @@ static void kill_me_maybe(struct callback_head *cb)
>  		set_mce_nospec(p->mce_addr >> PAGE_SHIFT, p->mce_whole_page);
>  		sync_core();
>  		return;
> -	}
> -
> -	/*
> -	 * -EHWPOISON from memory_failure() means that it already sent SIGBUS
> -	 * to the current process with the proper error info, so no need to
> -	 * send SIGBUS here again.
> -	 */
> -	if (ret == -EHWPOISON)
> +	} else if (ret == -EHWPOISON || ret == 1)
> +		/*
> +		 * -EHWPOISON from memory_failure() means that it already sent SIGBUS
> +		 * to the current process with the proper error info, so no need to
> +		 * send SIGBUS here again.
> +		 *
> +		 * 1 means it's a filter page, no need to deal with.
> +		 */

The new return code 1 seems to be handled in the same manner as -EHWPOISON,
so how about simply using -EHWPOISON as return code for the new case?
Then, the meaning of -EHWPOISON at this context would change like below:

 	/*
-	 * -EHWPOISON from memory_failure() means that it already sent SIGBUS
-	 * to the current process with the proper error info, so no need to
-	 * send SIGBUS here again.
+        * -EHWPOISON from memory_failure() means that memory_failure() did
+	 * not handle the error event for the following reason:
+	 *   - SIGBUS has already been sent to the current process with the
+	 *     proper error info, or
+	 *   - hwpoison_filter() filtered the event,
+	 * so no need to deal with it more.
 	 */


Thanks,
Naoya Horiguchi

>  		return;
>  
>  	pr_err("Memory error not recovered");
> @@ -1320,7 +1320,7 @@ static void kill_me_never(struct callback_head *cb)
>  
>  	p->mce_count = 0;
>  	pr_err("Kernel accessed poison in user space at %llx\n", p->mce_addr);
> -	if (!memory_failure(p->mce_addr >> PAGE_SHIFT, 0))
> +	if (!memory_failure(p->mce_addr >> PAGE_SHIFT, MF_MCE_HANDLE))
>  		set_mce_nospec(p->mce_addr >> PAGE_SHIFT, p->mce_whole_page);
>  }
>  
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 213cc569b192..f4703f948e9a 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -3188,6 +3188,7 @@ enum mf_flags {
>  	MF_MUST_KILL = 1 << 2,
>  	MF_SOFT_OFFLINE = 1 << 3,
>  	MF_UNPOISON = 1 << 4,
> +	MF_MCE_HANDLE = 1 << 5,
>  };
>  extern int memory_failure(unsigned long pfn, int flags);
>  extern void memory_failure_queue(unsigned long pfn, int flags);
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 97a9ed8f87a9..1a0bd91a685b 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1526,7 +1526,10 @@ static int memory_failure_hugetlb(unsigned long pfn, int flags)
>  				if (TestClearPageHWPoison(head))
>  					num_poisoned_pages_dec();
>  				unlock_page(head);
> -				return 0;
> +				if (flags & MF_MCE_HANDLE)
> +					return 1;
> +				else
> +					return 0;
>  			}
>  			unlock_page(head);
>  			res = MF_FAILED;
> @@ -1545,6 +1548,17 @@ static int memory_failure_hugetlb(unsigned long pfn, int flags)
>  	lock_page(head);
>  	page_flags = head->flags;
>  
> +	if (hwpoison_filter(p)) {
> +		if (TestClearPageHWPoison(head))
> +			num_poisoned_pages_dec();
> +		put_page(p);
> +		if (flags & MF_MCE_HANDLE)
> +			res = 1;
> +		else
> +			res = 0;
> +		goto out;
> +	}
> +
>  	/*
>  	 * TODO: hwpoison for pud-sized hugetlb doesn't work right now, so
>  	 * simply disable it. In order to make it work properly, we need
> @@ -1613,7 +1627,10 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
>  		goto out;
>  
>  	if (hwpoison_filter(page)) {
> -		rc = 0;
> +		if (flags & MF_MCE_HANDLE)
> +			rc = 1;
> +		else
> +			rc = 0;
>  		goto unlock;
>  	}
>  
> @@ -1837,6 +1854,10 @@ int memory_failure(unsigned long pfn, int flags)
>  			num_poisoned_pages_dec();
>  		unlock_page(p);
>  		put_page(p);
> +		if (flags & MF_MCE_HANDLE)
> +			res = 1;
> +		else
> +			res = 0;
>  		goto unlock_mutex;
>  	}
>  
> -- 
> 2.27.0