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

Souptick Joarder
2020-06-26T06:48:41Z

On Fri, Jun 26, 2020 at 11:22 AM Jürgen Groß <jgross@suse.com> wrote:
>
> 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]?

I fixed it in compile branch, but missed it in patch creation work
space at the time of posting.
I think, this is the compile error Boris was pointing to.
Sorry about it. I will fix it and post the v2.

>
> > + 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