[Intel-gfx] [PATCH v3] drm/i915: Enable guest i915 full ppgtt functionality

[Joonas Lahtinen]

On ke, 2017-05-31 at 10:49 +0800, Zhenyu Wang wrote:
> On 2017.05.30 11:37:50 +0300, Joonas Lahtinen wrote:
> > 
> > I just noticed there is INTEL_VGT_IF_VERSION when I was looking to make
> > sure that vgt_if is zeroed. Neither the version is incremented nor do I
> > see VGT_PVINFO_PAGE getting zeroed.
> > 
> > What measures are in place to make sure running a new i915 under older
> > DOM0 won't result in corruption?
> > 
> > The dependencies between i915 and gvt are rather tricky, so we'd need
> > INTEL_VGT_IF_VERSION minor increment and also a one line change
> > (zeroing of the new caps register) from gvt code to the same patch,
> > otherwise bisecting will break.
> > 
> 
> That's unfortunate...We can't increment minor now as it would break
> older guest, need to fix guest pvinfo version compat check, and new caps
> field is kept as zero if not used, so now depend on that for compatibility.

Point of minor versions is to indicate no breaking, but to detect new
features.

But the damage has already been done, so it'd be worthwhile to document
this via a comment.

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