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Date:   Wed, 5 Jul 2023 16:57:05 -0700
From:   Mike Kravetz <mike.kravetz@oracle.com>
To:     Jiaqi Yan <jiaqiyan@google.com>
Cc:     naoya.horiguchi@nec.com, songmuchun@bytedance.com,
        shy828301@gmail.com, linmiaohe@huawei.com,
        akpm@linux-foundation.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, duenwen@google.com,
        axelrasmussen@google.com, jthoughton@google.com
Subject: Re: [PATCH v2 2/4] mm/hwpoison: check if a subpage of a hugetlb
 folio is raw HWPOISON
Message-ID: <20230705235705.GE41006@monkey>
References: <20230623164015.3431990-1-jiaqiyan@google.com>
 <20230623164015.3431990-3-jiaqiyan@google.com>
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On 06/23/23 16:40, Jiaqi Yan wrote:
> Adds the functionality to tell if a subpage of a hugetlb folio is a
> raw HWPOISON page. This functionality relies on RawHwpUnreliable to
> be not set; otherwise hugepage's HWPOISON list becomes meaningless.
> 
> Exports this functionality to be immediately used in the read operation
> for hugetlbfs.
> 
> Signed-off-by: Jiaqi Yan <jiaqiyan@google.com>
> ---
>  include/linux/hugetlb.h | 19 +++++++++++++++++++
>  include/linux/mm.h      |  7 +++++++
>  mm/hugetlb.c            | 10 ++++++++++
>  mm/memory-failure.c     | 34 ++++++++++++++++++++++++----------
>  4 files changed, 60 insertions(+), 10 deletions(-)
> 
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index 21f942025fec..8b73a12b7b38 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -1013,6 +1013,25 @@ void hugetlb_register_node(struct node *node);
>  void hugetlb_unregister_node(struct node *node);
>  #endif
>  
> +/*
> + * Struct raw_hwp_page represents information about "raw error page",
> + * constructing singly linked list from ->_hugetlb_hwpoison field of folio.
> + */
> +struct raw_hwp_page {
> +	struct llist_node node;
> +	struct page *page;
> +};
> +
> +static inline struct llist_head *raw_hwp_list_head(struct folio *folio)
> +{
> +	return (struct llist_head *)&folio->_hugetlb_hwpoison;
> +}
> +
> +/*
> + * Check if a given raw @subpage in a hugepage @folio is HWPOISON.
> + */
> +bool is_raw_hwp_subpage(struct folio *folio, struct page *subpage);
> +
>  #else	/* CONFIG_HUGETLB_PAGE */
>  struct hstate {};
>  
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 66032f0d515c..41a283bd41a7 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -3671,6 +3671,7 @@ extern const struct attribute_group memory_failure_attr_group;
>  extern void memory_failure_queue(unsigned long pfn, int flags);
>  extern int __get_huge_page_for_hwpoison(unsigned long pfn, int flags,
>  					bool *migratable_cleared);
> +extern bool __is_raw_hwp_subpage(struct folio *folio, struct page *subpage);
>  void num_poisoned_pages_inc(unsigned long pfn);
>  void num_poisoned_pages_sub(unsigned long pfn, long i);
>  struct task_struct *task_early_kill(struct task_struct *tsk, int force_early);
> @@ -3685,6 +3686,12 @@ static inline int __get_huge_page_for_hwpoison(unsigned long pfn, int flags,
>  	return 0;
>  }
>  
> +static inline bool __is_raw_hwp_subpage(struct folio *folio,
> +					struct page *subpage)
> +{
> +	return false;
> +}
> +
>  static inline void num_poisoned_pages_inc(unsigned long pfn)
>  {
>  }
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index ea24718db4af..6b860de87590 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -7377,6 +7377,16 @@ int get_huge_page_for_hwpoison(unsigned long pfn, int flags,
>  	return ret;
>  }
>  
> +bool is_raw_hwp_subpage(struct folio *folio, struct page *subpage)
> +{
> +	bool ret;
> +
> +	spin_lock_irq(&hugetlb_lock);
> +	ret = __is_raw_hwp_subpage(folio, subpage);
> +	spin_unlock_irq(&hugetlb_lock);

Can you describe what races the hugetlb_lock prevents here?
-- 
Mike Kravetz

> +	return ret;
> +}
> +
>  void folio_putback_active_hugetlb(struct folio *folio)
>  {
>  	spin_lock_irq(&hugetlb_lock);
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index c415c3c462a3..891248e2930e 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1809,18 +1809,32 @@ EXPORT_SYMBOL_GPL(mf_dax_kill_procs);
>  #endif /* CONFIG_FS_DAX */
>  
>  #ifdef CONFIG_HUGETLB_PAGE
> -/*
> - * Struct raw_hwp_page represents information about "raw error page",
> - * constructing singly linked list from ->_hugetlb_hwpoison field of folio.
> - */
> -struct raw_hwp_page {
> -	struct llist_node node;
> -	struct page *page;
> -};
>  
> -static inline struct llist_head *raw_hwp_list_head(struct folio *folio)
> +bool __is_raw_hwp_subpage(struct folio *folio, struct page *subpage)
>  {
> -	return (struct llist_head *)&folio->_hugetlb_hwpoison;
> +	struct llist_head *raw_hwp_head;
> +	struct raw_hwp_page *p, *tmp;
> +	bool ret = false;
> +
> +	if (!folio_test_hwpoison(folio))
> +		return false;
> +
> +	/*
> +	 * When RawHwpUnreliable is set, kernel lost track of which subpages
> +	 * are HWPOISON. So return as if ALL subpages are HWPOISONed.
> +	 */
> +	if (folio_test_hugetlb_raw_hwp_unreliable(folio))
> +		return true;
> +
> +	raw_hwp_head = raw_hwp_list_head(folio);
> +	llist_for_each_entry_safe(p, tmp, raw_hwp_head->first, node) {
> +		if (subpage == p->page) {
> +			ret = true;
> +			break;
> +		}
> +	}
> +
> +	return ret;
>  }
>  
>  static unsigned long __folio_free_raw_hwp(struct folio *folio, bool move_flag)
> -- 
> 2.41.0.162.gfafddb0af9-goog
>