linux-kernel - Re: [PATCH RESEND] drm/via: use get_user_pages

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20170301084326.tdz32zvjg62znclq@phenom.ffwll.local>
Date:   Wed, 1 Mar 2017 09:43:26 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Lorenzo Stoakes <lstoakes@...il.com>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        dri-devel@...ts.freedesktop.org, linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH RESEND] drm/via: use get_user_pages_unlocked()

On Tue, Feb 28, 2017 at 08:28:08PM +0000, Lorenzo Stoakes wrote:
> On 28 February 2017 at 19:35, Al Viro <viro@...iv.linux.org.uk> wrote:
> > On Tue, Feb 28, 2017 at 10:01:10AM +0100, Daniel Vetter wrote:
> >
> >> > +   ret = get_user_pages_unlocked((unsigned long)xfer->mem_addr,
> >> > +                   vsg->num_pages, vsg->pages,
> >> > +                   (vsg->direction == DMA_FROM_DEVICE) ? FOLL_WRITE : 0);
> >
> > Umm...  Why not
> >         ret = get_user_pages_fast((unsigned long)xfer->mem_addr,
> >                         vsg->num_pages,
> >                         vsg->direction == DMA_FROM_DEVICE,
> >                         vsg->pages);
> >
> > IOW, do you really need a warranty that ->mmap_sem will be grabbed and
> > released?
> 
> Daniel will be better placed to answer in this specific case, but more
> generally is there any reason why we can't just use
> get_user_pages_fast() in all such cases? These patches were simply a
> mechanical/cautious replacement for code that is more or less exactly
> equivalent but if this would make sense perhaps it'd be worth using
> gup_fast() where possible?

I have no idea. drm/via is unmaintained, it's a dri1 racy driver with
problems probably everywhere, and I'm not sure we even have someone left
who cares (there's an out-of-tree kms conversion of via, but it's stuck
since years).

In short, it's the drm dungeons and the only reason I merge patches is to
give people an easy target for test driving the patch submission process
to dri-devel. And to avoid drm being a blocker for tree-wide refactorings.
Otherwise 0 reasons to change anything here.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch