RE: [PATCH v3 1/3] xen/privcmd: Corrected error handling path

[Paul Durrant <xadimgnik@xxxxxxxxx>]

> -----Original Message-----
> From: Souptick Joarder <jrdr.linux@xxxxxxxxx>
> Sent: 12 July 2020 04:40
> To: boris.ostrovsky@xxxxxxxxxx; jgross@xxxxxxxx; sstabellini@xxxxxxxxxx
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Souptick 
> Joarder
> <jrdr.linux@xxxxxxxxx>; John Hubbard <jhubbard@xxxxxxxxxx>; Paul Durrant 
> <xadimgnik@xxxxxxxxx>
> Subject: [PATCH v3 1/3] xen/privcmd: Corrected error handling path
> 
> 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.
> 
> Signed-off-by: Souptick Joarder <jrdr.linux@xxxxxxxxx>
> Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
> Cc: John Hubbard <jhubbard@xxxxxxxxxx>
> Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> Cc: Paul Durrant <xadimgnik@xxxxxxxxx>

Reviewed-by: Paul Durrant <paul@xxxxxxx>

> ---
>  drivers/xen/privcmd.c | 31 +++++++++++++++----------------
>  1 file changed, 15 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
> index 5dfc59f..b001673 100644
> --- a/drivers/xen/privcmd.c
> +++ b/drivers/xen/privcmd.c
> @@ -579,13 +579,13 @@ 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, unsigned int *pinned)
>  {
>       unsigned int i;
> 
>       for (i = 0; i < num; i++) {
>               unsigned int requested;
> -             int pinned;
> +             int page_count;
> 
>               requested = DIV_ROUND_UP(
>                       offset_in_page(kbufs[i].uptr) + kbufs[i].size,
> @@ -593,14 +593,15 @@ static int lock_pages(
>               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)
> +                     return page_count;
> 
> -             nr_pages -= pinned;
> -             pages += pinned;
> +             *pinned += page_count;
> +             nr_pages -= page_count;
> +             pages += page_count;
>       }
> 
>       return 0;
> @@ -610,13 +611,8 @@ 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]);
> -     }
> +     for (i = 0; i < nr_pages; i++)
> +             put_page(pages[i]);
>  }
> 
>  static long privcmd_ioctl_dm_op(struct file *file, void __user *udata)
> @@ -629,6 +625,7 @@ static long privcmd_ioctl_dm_op(struct file *file, void 
> __user *udata)
>       struct xen_dm_op_buf *xbufs = NULL;
>       unsigned int i;
>       long rc;
> +     unsigned int pinned = 0;
> 
>       if (copy_from_user(&kdata, udata, sizeof(kdata)))
>               return -EFAULT;
> @@ -682,9 +679,11 @@ 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);
> --
> 1.9.1