linux-kernel - Re: [PATCH 3.16.y-ckt 075/216] drm/i915: Disallow pin ioctl completely for kms drivers

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Date:	Tue, 13 Jan 2015 19:33:57 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Chris Wilson <chris@...is-wilson.co.uk>,
	Daniel Vetter <daniel.vetter@...el.com>,
	Thomas Voegtle <tv@...96.de>
Subject: Re: [PATCH 3.16.y-ckt 075/216] drm/i915: Disallow pin ioctl
 completely for kms drivers

On Mon, Jan 12, 2015 at 06:03:12PM +0000, Luis Henriques wrote:
> 3.16.7-ckt4 -stable review patch.  If anyone has any objections, please let me know.
>

Hi Daniel and Chris,

Thomas Voegtle (on Cc:) reported a regression in 3.16.7-ckt4, and he
traced the issue to this commit.  You can see the whole thread in the
3.16.7-ckt4 stable review email, or here:

 http://thread.gmane.org/gmane.linux.kernel.stable/119818/focus=120043

Any suggestions/ideas before I drop this patch?  It seems odd to me
that this patch causes a memory leak, but I don't really know the
code.

Cheers,
--
Luís

> ------------------
> 
> From: Daniel Vetter <daniel.vetter@...ll.ch>
> 
> commit d472fcc8379c062bd56a3876fc6ef22258f14a91 upstream.
> 
> The problem here is that SNA pins batchbuffers to etch out a bit more
> performance. Iirc it started out as a w/a for i830M (which we've
> implemented in the kernel since a long time already). The problem is
> that the pin ioctl wasn't added in
> 
> commit d23db88c3ab233daed18709e3a24d6c95344117f
> Author: Chris Wilson <chris@...is-wilson.co.uk>
> Date:   Fri May 23 08:48:08 2014 +0200
> 
>     drm/i915: Prevent negative relocation deltas from wrapping
> 
> Fix this by simply disallowing pinning from userspace so that the
> kernel is in full control of batch placement again. Especially since
> distros are moving towards running X as non-root, so most users won't
> even be able to see any benefits.
> 
> UMS support is dead now, but we need this minimal patch for
> backporting. Follow-up patch will remove the pin ioctl code
> completely.
> 
> Note to backporters: You must have both
> 
> commit b45305fce5bb1abec263fcff9d81ebecd6306ede
> Author: Daniel Vetter <daniel.vetter@...ll.ch>
> Date:   Mon Dec 17 16:21:27 2012 +0100
> 
>     drm/i915: Implement workaround for broken CS tlb on i830/845
> 
> which laned in 3.8 and
> 
> commit c4d69da167fa967749aeb70bc0e94a457e5d00c1
> Author: Chris Wilson <chris@...is-wilson.co.uk>
> Date:   Mon Sep 8 14:25:41 2014 +0100
> 
>     drm/i915: Evict CS TLBs between batches
> 
> which is also marked cc: stable. Otherwise this could introduce a
> regression by disabling the userspace w/a without the kernel w/a being
> fully functional on i830/45.
> 
> References: https://bugs.freedesktop.org/show_bug.cgi?id=76554#c116
> Cc: Chris Wilson <chris@...is-wilson.co.uk>
> Signed-off-by: Daniel Vetter <daniel.vetter@...el.com>
> Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
> ---
>  drivers/gpu/drm/i915/i915_gem.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index ef3b4798da02..05cf35a972e5 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -4129,7 +4129,7 @@ i915_gem_pin_ioctl(struct drm_device *dev, void *data,
>  	struct drm_i915_gem_object *obj;
>  	int ret;
>  
> -	if (INTEL_INFO(dev)->gen >= 6)
> +	if (drm_core_check_feature(dev, DRIVER_MODESET))
>  		return -ENODEV;
>  
>  	ret = i915_mutex_lock_interruptible(dev);
> @@ -4222,6 +4222,9 @@ i915_gem_busy_ioctl(struct drm_device *dev, void *data,
>  	struct drm_i915_gem_object *obj;
>  	int ret;
>  
> +	if (drm_core_check_feature(dev, DRIVER_MODESET))
> +		return -ENODEV;
> +
>  	ret = i915_mutex_lock_interruptible(dev);
>  	if (ret)
>  		return ret;
> -- 
> 2.1.4
> 
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