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From: Thomas Hellstrom <thellstrom@vmware.com>
To: "emil.l.velikov@gmail.com" <emil.l.velikov@gmail.com>
Cc: "kernel@collabora.com" <kernel@collabora.com>,
	Linux-graphics-maintainer <Linux-graphics-maintainer@vmware.com>,
	"dri-devel@lists.freedesktop.org"
	<dri-devel@lists.freedesktop.org>
Subject: Re: [PATCH 4/5] drm/vmwgfx: remove custom ioctl io encoding check
Date: Fri, 24 May 2019 22:39:53 +0000	[thread overview]
Message-ID: <27cb3f6d2002edcf45a4d50e6cef0854ba80766a.camel@vmware.com> (raw)
In-Reply-To: <20190524152648.GD8938@arch-x1c3>

Hi, Emil

On Fri, 2019-05-24 at 16:26 +0100, Emil Velikov wrote:
> On 2019/05/24, Thomas Hellstrom wrote:
> > On Fri, 2019-05-24 at 13:14 +0100, Emil Velikov wrote:
> > > On 2019/05/23, Thomas Hellstrom wrote:
> > > > Hi, Emil,
> > > > 
> > > > On Wed, 2019-05-22 at 17:41 +0100, Emil Velikov wrote:
> > > > > From: Emil Velikov <emil.velikov@collabora.com>
> > > > > 
> > > > > Drop the custom ioctl io encoding check - core drm does it
> > > > > for
> > > > > us.
> > > > 
> > > > I fail to see where the core does this, or do I miss something?
> > > 
> > > drm_ioctl() allows for the encoding to be changed and attributes
> > > that
> > > only the
> > > appropriate size is copied in/out of the kernel.
> > > 
> > > Technically the function is more relaxed relative to the vmwgfx
> > > check, yet
> > > seems perfectly reasonable.
> > > 
> > > Is there any corner-case that isn't but should be handled in
> > > drm_ioctl()?
> > 
> > I'd like to turn the question around and ask whether there's a
> > reason
> > we should relax the vmwgfx test? In the past it has trapped quite a
> > few
> > user-space errors.
> > 
> The way I see it either:
>  - the check, as-is, is unnessesary, or
>  - it is needed, and we should do something equivalent for all of DRM
> 
> We had a very long brainstorming session with a colleague and we
> could not see
> any cases where this would cause a problem. If you recall anything
> concrete
> please let me know - I would be more than happy to take a closer
> look.

If you have a good reason to drop an ioctl sanity check, I'd be
perfectly happy to do it. To me, a good reason even includes "I have a
non-open-source customer having problems with this check" because of
reason etc. etc. as long as I have a way to evaluate those reasons and
determine if they're valid or not. "No other drm driver nor the core is
doing this" is NOT a valid reason to me. In particular if the check is
not affecting performance. So unless you provide additional reasons to
drop this check, it's a solid NAK from my side.

Thanks,
Thomas


> 
> Thanks
> Emil
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  reply	other threads:[~2019-05-24 22:40 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-22 16:41 [PATCH 1/5] vmwgfx: drop empty lastclose stub Emil Velikov
2019-05-22 16:41 ` [PATCH 2/5] drm/vmgfx: kill off unused init_mutex Emil Velikov
2019-05-23  6:48   ` Thomas Hellstrom
2019-05-22 16:41 ` [PATCH 3/5] drm/vmwgfx: use core drm to extend/check vmw_execbuf_ioctl Emil Velikov
2019-05-22 19:01   ` Thomas Hellstrom
2019-05-22 19:09     ` Daniel Vetter
2019-05-24  6:05       ` Thomas Hellstrom
2019-05-24  7:46         ` Daniel Vetter
2019-05-24 10:53           ` Emil Velikov
2019-05-24 10:56             ` Thomas Hellstrom
2019-05-23  8:52   ` Thomas Hellstrom
2019-05-22 16:41 ` [PATCH 4/5] drm/vmwgfx: remove custom ioctl io encoding check Emil Velikov
2019-05-23  6:44   ` Thomas Hellstrom
2019-05-24 12:14     ` Emil Velikov
2019-05-24 13:04       ` Thomas Hellstrom
2019-05-24 15:26         ` Emil Velikov
2019-05-24 22:39           ` Thomas Hellstrom [this message]
2019-05-25  8:25             ` Thomas Hellstrom
2019-05-27  9:08               ` Emil Velikov
2019-05-27 11:34                 ` Thomas Hellstrom
2019-05-27 12:35                   ` Emil Velikov
2019-05-27 13:44                     ` Thomas Hellstrom
2019-05-27 15:27                       ` Emil Velikov
2019-05-27 15:50                         ` Thomas Hellstrom
2019-05-27 16:36                           ` Emil Velikov
2019-05-22 16:41 ` [PATCH 5/5] drm: make drm_ioctl_permit() internal Emil Velikov
2019-05-23  6:47 ` [PATCH 1/5] vmwgfx: drop empty lastclose stub Thomas Hellstrom

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