Date: Mon, 15 Dec 2014 12:17:03 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
To: "LF.Tan" <lftan.linux@gmail.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Arnd Bergmann <arnd@arndb.de>, Linux-Arch <linux-arch@vger.kernel.org>
Subject: Re: [PATCH 00/18] uaccess: fix sparse warning on get_user for
 bitwise types
Message-ID: <20141215101703.GA26156@redhat.com>
References: <1418575877-21488-1-git-send-email-mst@redhat.com>
 <CAFiDJ5_fGWx2E1jvU+k0Tv_esRpWmC-p+kq7Y_VOr5bx2ZUFzg@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAFiDJ5_fGWx2E1jvU+k0Tv_esRpWmC-p+kq7Y_VOr5bx2ZUFzg@mail.gmail.com>
Sender: linux-kernel-owner@vger.kernel.org

On Mon, Dec 15, 2014 at 06:03:10PM +0800, LF.Tan wrote:
> On Mon, Dec 15, 2014 at 12:51 AM, Michael S. Tsirkin <mst@redhat.com> wrote:
> > At the moment, if p and x are both tagged as bitwise types,
> > get_user(x, p) produces a sparse warning on many architectures.
> > This is because *p on these architectures is loaded into long
> > (typically using asm), then cast back to typeof(*p).
> >
> > When typeof(*p) is a bitwise type (which is uncommon), such a cast needs
> > __force, otherwise sparse produces a warning.
> >
> > Some architectures already have the __force tag, add it
> > where it's missing.
> >
> > Specificlly, vhost wants to read bitwise types from userspace using get_user.
> > At the moment this triggers sparse errors, since the value is passed through an
> > integer.
> >
> > For now, I worked around this by converting vhost code to access_ok +
> > __get_user, but that's not robust, I'd like to switch to get_user for 3.19.
> >
> > I tested this on x86 only so far. Since it's just adding __force, should be
> > trivially safe everywhere?
> >
> > Please review, and consider for 3.19.
> >
> > Who can merge this? Arnd?
> Hi Michael
> 
> FYI, there is new arch (arch/nios2) in 3.19. Is your patchset include
> the fix for it?
> Thanks.
> 
> Regards
> Ley Foon

Thanks for the heads up.
No - it will probably need a similar fix for __get_user and get_user.
It's just a parse warning so it's not a blocker.
Can you fix it yourself or prefer me to?

-- 
MST
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/