[Intel-gfx] [PATCH] drm/i915: Move the release of PT page to the upper caller

[Chris Wilson]

On Tue, Nov 22, 2016 at 09:29:40PM +0800, Zhi Wang wrote:
> Hi guys:
>     Would you mind to have a quick review on this patch? :P The
> linux guest under GVT-g couldn't boot up without this patch in the
> newer kernel.
> 
> Thanks,
> Zhi.
> 
> On 11/21/16 19:44, Zhi Wang wrote:
> >a PT page will be released if it doesn't contain any meaningful mappings
> >during PPGTT page table shrinking. The PT entry in the upper level will
> >be set to a scratch entry.
> >
> >Normally this works nicely, but in virtualization world, the PPGTT page
> >table is tracked by hypervisor. Releasing the PT page before modifying
> >the upper level PT entry would cause extra efforts.
> >
> >As the tracked page has been returned to OS before losing track from
> >hypervisor, it could be written in any pattern. Hypervisor has to recognize
> >if a page is still being used as a PT page by validating these writing
> >patterns. It's complicated. Better let the guest modify the PT entry in
> >upper level PT first, then release the PT page.
> >
> >Cc: Michał Winiarski <michal.winiarski at intel.com>
> >Cc: Michel Thierry <michel.thierry at intel.com>
> >Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> >Cc: Chris Wilson <chris at chris-wilson.co.uk>
> >Cc: Zhenyu Wang <zhenyuw at linux.intel.com>
> >Cc: Zhiyuan Lv <zhiyuan.lv at intel.com>
> >Signed-off-by: Zhi Wang <zhi.a.wang at intel.com>

The original didn't make it to me, so I just assumed a list issue.

For the record, I'd like to have some more detail on just when the hv is
doing the page scanning. It makes it sound like you are actively
scanning an idle range.

Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre