[Intel-gfx] [PATCH] drm/i915: Serialize GTT Updates on BXT

[Bloomfield, Jon]

> -----Original Message-----
> From: Chris Wilson [mailto:chris at chris-wilson.co.uk]
> Sent: Tuesday, May 23, 2017 1:41 AM
> To: Bloomfield, Jon <jon.bloomfield at intel.com>
> Cc: intel-gfx at lists.freedesktop.org
> Subject: Re: [Intel-gfx] [PATCH] drm/i915: Serialize GTT Updates on BXT
> 
> On Mon, May 22, 2017 at 11:07:25AM -0700, Jon Bloomfield wrote:
> > BXT requires accesses to the GTT (i.e. PTE updates) to be serialized
> > when IOMMU is enabled. This patch guarantees this by wrapping all
> > updates in stop_machine and using a flushing read to guarantee that
> > the GTT writes have reached their destination before restarting.
> >
> 
> Testcase? igt/gem_concurrent_blit shows the failure.

I was using a combination of tests, run in parallel to hit this bug. I need to get hold of
a system again to re-run. Are you saying you have also repro'd the bug just with
gem_concurrent_blit or just suggesting that it might be a good candidate ?

I'll also re-try without the flushing read, but I'm wary of removing this unless I can
understand why the mmio write has the same effect. It might be luck.

> -Chris
> 
> --
> Chris Wilson, Intel Open Source Technology Centre