[Intel-gfx] [PATCH v3] drm/i915/gvt: return the actual aperture size under gvt environment

[Li, Weinan Z]

Thanks Chris.
> -----Original Message-----
> From: Chris Wilson [mailto:chris at chris-wilson.co.uk]
> Sent: Monday, May 8, 2017 8:11 PM
> To: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> Cc: Li, Weinan Z <weinan.z.li at intel.com>; intel-gfx at lists.freedesktop.org; intel-
> gvt-dev at lists.freedesktop.org
> Subject: Re: [PATCH v3] drm/i915/gvt: return the actual aperture size under gvt
> environment
> 
> On Mon, May 08, 2017 at 01:18:38PM +0300, Joonas Lahtinen wrote:
> > On ma, 2017-05-08 at 02:49 +0000, Li, Weinan Z wrote:
> > > Hi Joonas/Chris, do you have any comments?
> > > I've asked OCL team for this patch, they also agree to use available
> > > aperture size for max allocation buffer definition, code confirmation
> ongoing.
> >
> > The patch title should be corrected to refer to usable aperture size.
> >
> > > > -----Original Message-----
> > > > From: Li, Weinan Z
> > > > Sent: Wednesday, May 3, 2017 8:51 AM
> > > > > > To: intel-gfx at lists.freedesktop.org;
> > > > > > intel-gvt-dev at lists.freedesktop.org
> > > > > > Cc: Li, Weinan Z <weinan.z.li at intel.com>
> > > > Subject: [PATCH v3] drm/i915/gvt: return the actual aperture size
> > > > under gvt environment
> > > >
> > > > I915_GEM_GET_APERTURE ioctl is used to probe aperture size from
> userspace.
> > > > In gvt environment, each vm only use the ballooned part of
> > > > aperture, so we should return the actual available aperture size
> > > > exclude the reserved part by balloon.
> > > >
> > > > v2: add 'reserved' in struct i915_address_space to record the
> > > > reserved size in ggtt by balloon.
> > > >
> > > > v3: remain aper_size as total, adjust aper_available_size exclude
> > > > reserved and pinned. UMD driver need to adjust the max allocation
> > > > size according to the available aperture size but not total size.
> 
> Only adjusting aper_available_size prevents the immediate breakage wrt to
> libdrm_intel, but I'm worried about the fragility of userspace using this. What is
> it being used for? I doubt this is the right information for them, and generally
> whether it's a correct assumption by userspace.
This issue was found by OCL test in GVT-g Linux guest, actually it uses total aperture
size now, but if we adjust the total size, it may impact some other applications that
need use total size to check available GTT address(talked in the last mail loop).
So I talked with OCL team guys, they also agree to use usable aperture size.
For other applications, I am not sure. Any way we should return correct information
under GVT-g environment I think.
> 
> What happened to reporting the correct size via CONTEXT_PARAM_GTT_SIZE
> which doesn't have the same issues with userspace incorrectly using GGTT for
> PPGTT?
I remove it in this patch, since I haven't found any issues relate to
CONTEXT_PARAM_GTT_SIZE so far.
> -Chris
> 
> --
> Chris Wilson, Intel Open Source Technology Centre