Commit 38c1ddbd authored by Jiaqi Yan's avatar Jiaqi Yan Committed by Andrew Morton
Browse files

hugetlbfs: improve read HWPOISON hugepage 

When a hugepage contains HWPOISON pages, read() fails to read any byte of
the hugepage and returns -EIO, although many bytes in the HWPOISON
hugepage are readable.

Improve this by allowing hugetlbfs_read_iter returns as many bytes as
possible.  For a requested range [offset, offset + len) that contains
HWPOISON page, return [offset, first HWPOISON page addr); the next read
attempt will fail and return -EIO.

Link: https://lkml.kernel.org/r/20230713001833.3778937-4-jiaqiyan@google.com


Signed-off-by: default avatarJiaqi Yan <jiaqiyan@google.com>
Reviewed-by: default avatarMike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: default avatarNaoya Horiguchi <naoya.horiguchi@nec.com>
Cc: James Houghton <jthoughton@google.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent b79f8eb4

fs/hugetlbfs/inode.c

+51 −6
Original line number Diff line number Diff line
@@ -282,6 +282,41 @@ hugetlb_get_unmapped_area(struct file *file, unsigned long addr, 
}

#endif



/*

 * Someone wants to read @bytes from a HWPOISON hugetlb @page from @offset.

 * Returns the maximum number of bytes one can read without touching the 1st raw

 * HWPOISON subpage.

 *

 * The implementation borrows the iteration logic from copy_page_to_iter*.

 */

static size_t adjust_range_hwpoison(struct page *page, size_t offset, size_t bytes)

{

	size_t n = 0;

	size_t res = 0;



	/* First subpage to start the loop. */

	page += offset / PAGE_SIZE;

	offset %= PAGE_SIZE;

	while (1) {

		if (is_raw_hwpoison_page_in_hugepage(page))

			break;



		/* Safe to read n bytes without touching HWPOISON subpage. */

		n = min(bytes, (size_t)PAGE_SIZE - offset);

		res += n;

		bytes -= n;

		if (!bytes || !n)

			break;

		offset += n;

		if (offset == PAGE_SIZE) {

			page++;

			offset = 0;

		}

	}



	return res;

}



/*

 * Support for read() - Find the page attached to f_mapping and copy out the

 * data. This provides functionality similar to filemap_read().
@@ -300,7 +335,7 @@ static ssize_t hugetlbfs_read_iter(struct kiocb *iocb, struct iov_iter *to) 


	while (iov_iter_count(to)) {

		struct page *page;

		size_t nr, copied;

		size_t nr, copied, want;



		/* nr is the maximum number of bytes to copy from this page */

		nr = huge_page_size(h);
@@ -328,16 +363,26 @@ static ssize_t hugetlbfs_read_iter(struct kiocb *iocb, struct iov_iter *to) 
		} else {

			unlock_page(page);



			if (PageHWPoison(page)) {

			if (!PageHWPoison(page))

				want = nr;

			else {

				/*

				 * Adjust how many bytes safe to read without

				 * touching the 1st raw HWPOISON subpage after

				 * offset.

				 */

				want = adjust_range_hwpoison(page, offset, nr);

				if (want == 0) {

					put_page(page);

					retval = -EIO;

					break;

				}

			}



			/*

			 * We have the page, copy it to user space buffer.

			 */

			copied = copy_page_to_iter(page, offset, nr, to);

			copied = copy_page_to_iter(page, offset, want, to);

			put_page(page);

		}

		offset += copied;