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

Souptick Joarder
2020-06-26T05:36:33Z

On Fri, Jun 26, 2020 at 5:01 AM Boris Ostrovsky
<boris.ostrovsky@oracle.com> wrote:
>
> On 6/24/20 11:02 PM, 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.
>
>
> There are two unrelated changes here (improving error path and marking
> pages dirty), they should be handled by separate patches.

Sure, will do it in v2.

>
>
> (I assume marking pages dirty is something you want to go to stable tree
> since otherwise there is no reason for making this change)
>
>
> >
> > 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,
>
>
> I don't think so.

I compile test it against ARM and it was fine.
Against which ARCH is it failing ?

>
>
> > 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 i;
> > + int errno = 0, page_count = 0;
>
>
> No need for error, really --- you can return the value immediately.

yes, this is unnecessary.

>
>
> >
> > for (i = 0; i < num; i++) {
> > unsigned int requested;
> > - int pinned;
> >
> > + *pinned += page_count;
>
>
> I'd move this lower, after a successful call to get_user_pages_fast()
> (and then you won't need to initialize it)

Ok.

>
>
> > 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;
> > + }
> >
> > - nr_pages -= pinned;
> > - pages += pinned;
> > + nr_pages -= page_count;
> > + pages += page_count;
> > }
> >
> > - return 0;
> > + return errno;
> > }
> >
> > 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);
> > + put_page(pages[i]);
> > }
>
>
> This won't compile.
>
>
> -boris
>
>
>