Re: [PATCH] hugetlbfs: don't delete error page from pagecache

Mike Kravetz
2022-10-20T00:02:18Z

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
>