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: Jiaqi Yan <jiaqiyan@google.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: Naoya 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: Andrew Morton <akpm@linux-foundation.org>

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 7b17ccf..e7611ae 100644 (file)
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -283,6 +283,41 @@ 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)) {
-                               put_page(page);
-                               retval = -EIO;
-                               break;
+                       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;