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Date:   Wed, 19 Oct 2022 17:02:02 -0700
From:   Mike Kravetz <mike.kravetz@oracle.com>
To:     James Houghton <jthoughton@google.com>
Cc:     Muchun Song <songmuchun@bytedance.com>,
        Naoya Horiguchi <naoya.horiguchi@nec.com>,
        Miaohe Lin <linmiaohe@huawei.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Yang Shi <shy828301@gmail.com>,
        Axel Rasmussen <axelrasmussen@google.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] hugetlbfs: don't delete error page from pagecache
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References: <20221018200125.848471-1-jthoughton@google.com>
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On 10/18/22 20:01, James Houghton wrote:
> This change is very similar to the change that was made for shmem [1],
> and it solves the same problem but for HugeTLBFS instead.
> 
> Currently, when poison is found in a HugeTLB page, the page is removed
> from the page cache. That means that attempting to map or read that
> hugepage in the future will result in a new hugepage being allocated
> instead of notifying the user that the page was poisoned. As [1] states,
> this is effectively memory corruption.
> 
> The fix is to leave the page in the page cache. If the user attempts to
> use a poisoned HugeTLB page with a syscall, the syscall will fail with
> EIO, the same error code that shmem uses. For attempts to map the page,
> the thread will get a BUS_MCEERR_AR SIGBUS.
> 
> [1]: commit a76054266661 ("mm: shmem: don't truncate page if memory failure happens")
> 
> Signed-off-by: James Houghton <jthoughton@google.com>
> ---
>  fs/hugetlbfs/inode.c | 13 ++++++-------
>  mm/hugetlb.c         |  4 ++++
>  mm/memory-failure.c  |  5 ++++-
>  3 files changed, 14 insertions(+), 8 deletions(-)

Thanks James!

Code looks correct.  One observation below, but I do not suggest changing.

Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>

> 
> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
> index fef5165b73a5..7f836f8f9db1 100644
> --- a/fs/hugetlbfs/inode.c
> +++ b/fs/hugetlbfs/inode.c
> @@ -328,6 +328,12 @@ static ssize_t hugetlbfs_read_iter(struct kiocb *iocb, struct iov_iter *to)
>  		} else {
>  			unlock_page(page);
>  
> +			if (PageHWPoison(page)) {
> +				put_page(page);
> +				retval = -EIO;
> +				break;
> +			}
> +
>  			/*
>  			 * We have the page, copy it to user space buffer.
>  			 */
> @@ -1111,13 +1117,6 @@ static int hugetlbfs_migrate_folio(struct address_space *mapping,
>  static int hugetlbfs_error_remove_page(struct address_space *mapping,
>  				struct page *page)
>  {
> -	struct inode *inode = mapping->host;
> -	pgoff_t index = page->index;
> -
> -	hugetlb_delete_from_page_cache(page_folio(page));
> -	if (unlikely(hugetlb_unreserve_pages(inode, index, index + 1, 1)))
> -		hugetlb_fix_reserve_counts(inode);
> -
>  	return 0;
>  }
>  
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 97896165fd3f..5120a9ccbf5b 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -6101,6 +6101,10 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
>  
>  	ptl = huge_pte_lock(h, dst_mm, dst_pte);
>  
> +	ret = -EIO;
> +	if (PageHWPoison(page))
> +		goto out_release_unlock;
> +
>  	/*
>  	 * We allow to overwrite a pte marker: consider when both MISSING|WP
>  	 * registered, we firstly wr-protect a none pte which has no page cache
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 145bb561ddb3..bead6bccc7f2 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1080,6 +1080,7 @@ static int me_huge_page(struct page_state *ps, struct page *p)
>  	int res;
>  	struct page *hpage = compound_head(p);
>  	struct address_space *mapping;
> +	bool extra_pins = false;
>  
>  	if (!PageHuge(hpage))
>  		return MF_DELAYED;
> @@ -1087,6 +1088,8 @@ static int me_huge_page(struct page_state *ps, struct page *p)
>  	mapping = page_mapping(hpage);
>  	if (mapping) {
>  		res = truncate_error_page(hpage, page_to_pfn(p), mapping);
> +		/* The page is kept in page cache. */

That looks a bit silly as we are know truncate_error_page() is a noop and call
it anyway.  I suppose we could just set 'res = MF_RECOVERED'.  However, it
really should be left as is in case more non-hugetlb functionality is added to
truncate_error_page() in the future.
-- 
Mike Kravetz

> +		extra_pins = true;
>  		unlock_page(hpage);
>  	} else {
>  		unlock_page(hpage);
> @@ -1104,7 +1107,7 @@ static int me_huge_page(struct page_state *ps, struct page *p)
>  		}
>  	}
>  
> -	if (has_extra_refcount(ps, p, false))
> +	if (has_extra_refcount(ps, p, extra_pins))
>  		res = MF_FAILED;
>  
>  	return res;
> -- 
> 2.38.0.413.g74048e4d9e-goog
>