Re: [PATCH v2 1/2] drm/i915: Introduce GEM proxy

[Joonas Lahtinen <joonas.lahtinen@linux.intel.com>]

On Tue, 2017-11-07 at 04:53 +0000, Zhang, Tina wrote:
> > -----Original Message-----
> > From: intel-gvt-dev [mailto:intel-gvt-dev-bounces@lists.freedesktop.org] On
> > Behalf Of Joonas Lahtinen
> > Sent: Monday, November 6, 2017 7:24 PM
> > To: Zhang, Tina <tina.zhang@intel.com>; zhenyuw@linux.intel.com; Wang, Zhi
> > A <zhi.a.wang@intel.com>; daniel@ffwll.ch; chris@chris-wilson.co.uk
> > Cc: Daniel Vetter <daniel.vetter@ffwll.ch>; intel-gfx@lists.freedesktop.org;
> > intel-gvt-dev@lists.freedesktop.org
> > Subject: Re: [PATCH v2 1/2] drm/i915: Introduce GEM proxy
> > 
> > On Wed, 2017-11-01 at 17:22 +0800, Tina Zhang wrote:
> > > GEM proxy is a kind of GEM, whose backing physical memory is pinned
> > > and produced by guest VM and is used by host as read only. With GEM
> > > proxy, host is able to access guest physical memory through GEM object
> > > interface. As GEM proxy is such a special kind of GEM, a new flag
> > > I915_GEM_OBJECT_IS_PROXY is introduced to ban host from changing the
> > > backing storage of GEM proxy.
> > > 
> > > v2:
> > > - return -ENXIO when pin and map pages of GEM proxy to kernel space.
> > >   (Chris)
> > > 
> > > Here are the histories of this patch in "Dma-buf support for Gvt-g"
> > > patch-set:
> > > 
> > > v14:
> > > - return -ENXIO when gem proxy object is banned by ioctl.
> > >   (Chris) (Daniel)
> > > 
> > > v13:
> > > - add comments to GEM proxy. (Chris)
> > > - don't ban GEM proxy in i915_gem_sw_finish_ioctl. (Chris)
> > > - check GEM proxy bar after finishing i915_gem_object_wait. (Chris)
> > > - remove GEM proxy bar in i915_gem_madvise_ioctl.
> > > 
> > > v6:
> > > - add gem proxy barrier in the following ioctls. (Chris)
> > >   i915_gem_set_caching_ioctl
> > >   i915_gem_set_domain_ioctl
> > >   i915_gem_sw_finish_ioctl
> > >   i915_gem_set_tiling_ioctl
> > >   i915_gem_madvise_ioctl
> > > 
> > > Signed-off-by: Tina Zhang <tina.zhang@intel.com>
> > > Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> > > Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
> > > Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> > 
> > <SNIP>
> > 
> > > @@ -1649,6 +1659,10 @@ i915_gem_sw_finish_ioctl(struct drm_device
> > 
> > *dev, void *data,
> > >  	if (!obj)
> > >  		return -ENOENT;
> > > 
> > > +	/* Proxy objects are barred from CPU access, so there is no
> > > +	 * need to ban sw_finish as it is a nop.
> > > +	 */
> > > +
> > >  	/* Pinned buffers may be scanout, so flush the cache */
> > >  	i915_gem_object_flush_if_display(obj);
> > >  	i915_gem_object_put(obj);
> > > @@ -2614,7 +2628,8 @@ void *i915_gem_object_pin_map(struct
> > 
> > drm_i915_gem_object *obj,
> > >  	void *ptr;
> > >  	int ret;
> > > 
> > > -	GEM_BUG_ON(!i915_gem_object_has_struct_page(obj));
> > > +	if (unlikely(!i915_gem_object_has_struct_page(obj)))
> > > +		return ERR_PTR(-ENODEV);
> > 
> > You should have marked this change in the changelog and then marked the
> > Reviewed-by tags to be valid only to the previous version of this patch.
> > 
> > It's not a fair game to claim a patch to be "Reviewed-by" at the current version,
> > when you've made changes that were not agreed upon.
> 
> I thought we were agreed on this :)
> 
> > 
> > So that's some meta-review. Back to the actual review;
> > 
> > Which codepath was hitting the GEM_BUG_ON? Wondering if it would be
> > cleaner to avoid the call to this function on that single codepath.
> 
> Here is the previously comments:
> https://lists.freedesktop.org/archives/intel-gvt-dev/2017-October/002278.html
> Thanks.

I never even noticed such an e-mail, so the correct response would've
been;

Reviewed-by: Joonas #vX
Reviewed-by: Chris

Where #vX is the version I actually agreed to.

Reviewed-by tags are are ones you need to be especially careful about
in addition to the Signed-off-bys because they carry special meaning:

https://www.kernel.org/doc/html/v4.13/process/submitting-patches.html#r
eviewer-s-statement-of-oversight

Regards, Joonas
-- 
Joonas Lahtinen
Open Source Technology Center
Intel Corporation
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