[PATCH v4 1/2] drm/i915: Add mechanism to submit a context WA on ring submission

[Chris Wilson]

Quoting Akeem G Abodunrin (2020-02-20 23:00:22)
> From: Mika Kuoppala <mika.kuoppala at linux.intel.com>
> 
> This patch adds framework to submit an arbitrary batchbuffer on each
> context switch to clear residual state for render engine on Gen7/7.5
> devices.
> 
> The idea of always emitting the context and vm setup around each request
> is primary to make reset recovery easy, and not require rewriting the
> ringbuffer. As each request would set up its own context, leaving it to
> the HW to notice and elide no-op context switches, we could restart the
> ring at any point, and reorder the requests freely.
> 
> However, to avoid emitting clear_residuals() between consecutive requests
> in the ringbuffer of the same context, we do want to track the current
> context in the ring. In doing so, we need to be careful to only record a
> context switch when we are sure the next request will be emitted.
> 
> This security mitigation change does not trigger any performance
> regression. Performance is on par with current mainline/drm-tip.
> 
> v2: Update vm_alias params to point to correct address space "vm" due to
> changes made in the patch "f21613797bae98773"
> 
> v3-v4: none
> 
> Signed-off-by: Mika Kuoppala <mika.kuoppala at linux.intel.com>
> Signed-off-by: Prathap Kumar Valsan <prathap.kumar.valsan at intel.com>
> Signed-off-by: Akeem G Abodunrin <akeem.g.abodunrin at intel.com>
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Balestrieri Francesco <francesco.balestrieri at intel.com>
> Cc: Bloomfield Jon <jon.bloomfield at intel.com>
> Cc: Dutt Sudeep <sudeep.dutt at intel.com>
Reviewed-by: Chris Wilson <chris.p.wilson at intel.com>
-Chris
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