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

[Jürgen Groß <jgross@xxxxxxxx>]

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@xxxxxxxxx>
> Cc: John Hubbard <jhubbard@xxxxxxxxxx>
> Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> Cc: Paul Durrant <xadimgnik@xxxxxxxxx>
> ---
> 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