Re: [PATCH 1/2] xen/privcmd: Corrected error handling path and mark pages dirty

Jürgen Groß
2020-06-26T05:52:26Z

On 25.06.20 05:02, Souptick Joarder wrote:
> Previously, if lock_pages() end up partially mapping pages, it used
> to return -ERRNO due to which unlock_pages() have to go through
> each pages[i] till *nr_pages* to validate them. This can be avoided
> by passing correct number of partially mapped pages & -ERRNO separately,
> while returning from lock_pages() due to error.
>
> With this fix unlock_pages() doesn't need to validate pages[i] till
> *nr_pages* for error scenario and few condition checks can be ignored.
>
> As discussed, pages need to be marked as dirty before unpinned it in
> unlock_pages() which was oversight.
>
> Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
> Cc: John Hubbard <jhubbard@nvidia.com>
> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> Cc: Paul Durrant <xadimgnik@gmail.com>
> ---
> Hi,
>
> I'm compile tested this, but unable to run-time test, so any testing
> help is much appriciated.
>
> drivers/xen/privcmd.c | 34 +++++++++++++++++++---------------
> 1 file changed, 19 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
> index a250d11..0da417c 100644
> --- a/drivers/xen/privcmd.c
> +++ b/drivers/xen/privcmd.c
> @@ -580,43 +580,44 @@ static long privcmd_ioctl_mmap_batch(
>
> static int lock_pages(
> struct privcmd_dm_op_buf kbufs[], unsigned int num,
> - struct page *pages[], unsigned int nr_pages)
> + struct page *pages[], unsigned int nr_pages, int *pinned)

unsigned int *pinned, please.

> {
> unsigned int i;
> + int errno = 0, page_count = 0;

Please drop the errno variable. It is misnamed (you never assign an
errno value to it) and not needed, as you can ...

>
> for (i = 0; i < num; i++) {
> unsigned int requested;
> - int pinned;
>
> + *pinned += page_count;
> requested = DIV_ROUND_UP(
> offset_in_page(kbufs[i].uptr) + kbufs[i].size,
> PAGE_SIZE);
> if (requested > nr_pages)
> return -ENOSPC;
>
> - pinned = get_user_pages_fast(
> + page_count = get_user_pages_fast(
> (unsigned long) kbufs[i].uptr,
> requested, FOLL_WRITE, pages);
> - if (pinned < 0)
> - return pinned;
> + if (page_count < 0) {
> + errno = page_count;
> + return errno;

... just return page_count her, and ...

> + }
>
> - nr_pages -= pinned;
> - pages += pinned;
> + nr_pages -= page_count;
> + pages += page_count;
> }
>
> - return 0;
> + return errno;

... leave this as it was.

> }
>
> static void unlock_pages(struct page *pages[], unsigned int nr_pages)
> {
> unsigned int i;
>
> - if (!pages)
> - return;
> -
> for (i = 0; i < nr_pages; i++) {
> - if (pages[i])
> - put_page(pages[i]);
> + if (!PageDirty(page))
> + set_page_dirty_lock(page);

page? Not pages[i]?

> + put_page(pages[i]);
> }
> }
>
> @@ -630,6 +631,7 @@ static long privcmd_ioctl_dm_op(struct file *file, void __user *udata)
> struct xen_dm_op_buf *xbufs = NULL;
> unsigned int i;
> long rc;
> + int pinned = 0;
>
> if (copy_from_user(&kdata, udata, sizeof(kdata)))
> return -EFAULT;
> @@ -683,9 +685,11 @@ static long privcmd_ioctl_dm_op(struct file *file, void __user *udata)
> goto out;
> }
>
> - rc = lock_pages(kbufs, kdata.num, pages, nr_pages);
> - if (rc)
> + rc = lock_pages(kbufs, kdata.num, pages, nr_pages, &pinned);
> + if (rc < 0) {
> + nr_pages = pinned;
> goto out;
> + }
>
> for (i = 0; i < kdata.num; i++) {
> set_xen_guest_handle(xbufs[i].h, kbufs[i].uptr);
>

Juergen