[Intel-gfx] [PATCH v2 1/2] drm/i915: Introduce GEM proxy

[Zhang, Tina]

> -----Original Message-----
> From: intel-gvt-dev [mailto:intel-gvt-dev-bounces at lists.freedesktop.org] On
> Behalf Of Joonas Lahtinen
> Sent: Monday, November 6, 2017 7:24 PM
> To: Zhang, Tina <tina.zhang at intel.com>; zhenyuw at linux.intel.com; Wang, Zhi
> A <zhi.a.wang at intel.com>; daniel at ffwll.ch; chris at chris-wilson.co.uk
> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>; intel-gfx at lists.freedesktop.org;
> intel-gvt-dev at 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 at intel.com>
> > Reviewed-by: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> > Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Daniel Vetter <daniel.vetter at 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.

BR,
Tina
> 
> Regards, Joonas
> --
> Joonas Lahtinen
> Open Source Technology Center
> Intel Corporation
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