linux-kernel - Re: [PATCH v2 2/3] xen/privcmd: Mark pages as dirty

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Date:   Tue, 7 Jul 2020 17:00:49 +0530
From:   Souptick Joarder <jrdr.linux@...il.com>
To:     Jürgen Groß <jgross@...e.com>
Cc:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        sstabellini@...nel.org, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org, John Hubbard <jhubbard@...dia.com>,
        Paul Durrant <xadimgnik@...il.com>
Subject: Re: [PATCH v2 2/3] xen/privcmd: Mark pages as dirty

On Tue, Jul 7, 2020 at 3:08 PM Jürgen Groß <jgross@...e.com> wrote:
>
> On 06.07.20 20:16, Souptick Joarder wrote:
> > pages need to be marked as dirty before unpinned it in
> > unlock_pages() which was oversight. This is fixed now.
> >
> > Signed-off-by: Souptick Joarder <jrdr.linux@...il.com>
> > Suggested-by: John Hubbard <jhubbard@...dia.com>
> > Cc: John Hubbard <jhubbard@...dia.com>
> > Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> > Cc: Paul Durrant <xadimgnik@...il.com>
> > ---
> >   drivers/xen/privcmd.c | 5 ++++-
> >   1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
> > index 33677ea..f6c1543 100644
> > --- a/drivers/xen/privcmd.c
> > +++ b/drivers/xen/privcmd.c
> > @@ -612,8 +612,11 @@ static void unlock_pages(struct page *pages[], unsigned int nr_pages)
> >   {
> >       unsigned int i;
> >
> > -     for (i = 0; i < nr_pages; i++)
> > +     for (i = 0; i < nr_pages; i++) {
> > +             if (!PageDirty(pages[i]))
> > +                     set_page_dirty_lock(pages[i]);
>
> With put_page() directly following I think you should be able to use
> set_page_dirty() instead, as there is obviously a reference to the page
> existing.

Patch [3/3] will convert above codes to use unpin_user_pages_dirty_lock()
which internally do the same check. So I thought to keep linux-stable and
linux-next code in sync. John had a similar concern [1] and later agreed to keep
this check.

Shall I keep this check ?  No ?

[1] https://lore.kernel.org/xen-devel/a750e5e5-fd5d-663b-c5fd-261d7c939ba7@nvidia.com/

>
> >               put_page(pages[i]);
> > +     }
> >   }
> >
> >   static long privcmd_ioctl_dm_op(struct file *file, void __user *udata)
> >
>
> Juergen