The patch titled
Subject: hugetlbfs: improve read HWPOISON hugepage
has been added to the -mm mm-unstable branch. Its filename is
hugetlbfs-improve-read-hwpoison-hugepage.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/hugetlbfs-improve-read-hwpoison-hugepage.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Jiaqi Yan <jiaqiyan@xxxxxxxxxx>
Subject: hugetlbfs: improve read HWPOISON hugepage
Date: Fri, 7 Jul 2023 20:19:03 +0000
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/20230707201904.953262-4-jiaqiyan@xxxxxxxxxx
Signed-off-by: Jiaqi Yan <jiaqiyan@xxxxxxxxxx>
Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Reviewed-by: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
Cc: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
Cc: James Houghton <jthoughton@xxxxxxxxxx>
Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Cc: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/hugetlbfs/inode.c | 58 ++++++++++++++++++++++++++++++++++++-----
1 file changed, 52 insertions(+), 6 deletions(-)
--- a/fs/hugetlbfs/inode.c~hugetlbfs-improve-read-hwpoison-hugepage
+++ a/fs/hugetlbfs/inode.c
@@ -283,6 +283,42 @@ hugetlb_get_unmapped_area(struct file *f
#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;
+ struct folio *folio = page_folio(page);
+
+ /* First subpage to start the loop. */
+ page += offset / PAGE_SIZE;
+ offset %= PAGE_SIZE;
+ while (1) {
+ if (is_raw_hwp_subpage(folio, 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 +336,7 @@ static ssize_t hugetlbfs_read_iter(struc
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 +364,26 @@ static ssize_t hugetlbfs_read_iter(struc
} 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;
_
Patches currently in -mm which might be from jiaqiyan@xxxxxxxxxx are
mm-hwpoison-delete-all-entries-before-traversal-in-__folio_free_raw_hwp.patch
mm-hwpoison-check-if-a-subpage-of-a-hugetlb-folio-is-raw-hwpoison.patch
hugetlbfs-improve-read-hwpoison-hugepage.patch
selftests-mm-add-tests-for-hwpoison-hugetlbfs-read.patch
