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.
Signed-off-by: Jiaqi Yan <jiaqiyan@google.com>
---
fs/hugetlbfs/inode.c | 58 +++++++++++++++++++++++++++++++++++++++-----
1 file changed, 52 insertions(+), 6 deletions(-)
diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 90361a922cec..86879ca3ff1e 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -282,6 +282,42 @@ 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;
+ 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(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 +364,26 @@ 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;
--
2.41.0.162.gfafddb0af9-googOn 06/23/23 16:40, Jiaqi Yan wrote:
> 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.
>
> Signed-off-by: Jiaqi Yan <jiaqiyan@google.com>
> ---
> fs/hugetlbfs/inode.c | 58 +++++++++++++++++++++++++++++++++++++++-----
> 1 file changed, 52 insertions(+), 6 deletions(-)
I went through the code and could not find any problems.
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
However, code like this is where I often make mistakes. So, it would be
great if someone else could take a look as well.
--
Mike Kravetz
>
> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
> index 90361a922cec..86879ca3ff1e 100644
> --- a/fs/hugetlbfs/inode.c
> +++ b/fs/hugetlbfs/inode.c
> @@ -282,6 +282,42 @@ 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;
> + 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(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 +364,26 @@ 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;
> --
> 2.41.0.162.gfafddb0af9-goog
>
On Fri, Jun 23, 2023 at 04:40:14PM +0000, Jiaqi Yan wrote: > 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. > > Signed-off-by: Jiaqi Yan <jiaqiyan@google.com> Looks good to me. Reviewed-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
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