[PATCH 3/3] drm/i915: Fix premature LRC unpin in GuC mode

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

In GuC mode LRC pinning lifetime depends exclusively on the
request liftime. Since that is terminated by the seqno update
that opens up a race condition between GPU finishing writing
out the context image and the driver unpinning the LRC.

To extend the LRC lifetime we will employ a similar approach
to what legacy ringbuffer submission does.

We will start tracking the last submitted context per engine
and keep it pinned until it is replaced by another one.

Note that the driver unload path is a bit fragile and could
benefit greatly from efforts to unify the legacy and exec
list submission code paths.

At the moment i915_gem_context_fini has special casing for the
two which are potentialy not needed, and also depends on
i915_gem_cleanup_ringbuffer running before itself.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Issue: VIZ-4277
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Nick Hoath <nicholas.hoath@intel.com>
---
I cannot test this with GuC but it passes BAT with execlists
and some real world smoke tests.
---
 drivers/gpu/drm/i915/i915_gem_context.c | 4 +++-
 drivers/gpu/drm/i915/intel_lrc.c        | 7 +++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index c25083c78ba7..0b419e165836 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -438,7 +438,9 @@ void i915_gem_context_fini(struct drm_device *dev)
 	for (i = 0; i < I915_NUM_RINGS; i++) {
 		struct intel_engine_cs *ring = &dev_priv->ring[i];
 
-		if (ring->last_context)
+		if (ring->last_context && i915.enable_execlists)
+			intel_lr_context_unpin(ring->last_context, ring);
+		else if (ring->last_context)
 			i915_gem_context_unreference(ring->last_context);
 
 		ring->default_context = NULL;
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 5c3f57fed916..b8a7e126d6d2 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -918,6 +918,7 @@ int intel_execlists_submission(struct i915_execbuffer_params *params,
 	struct intel_engine_cs  *ring = params->ring;
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct intel_ringbuffer *ringbuf = params->ctx->engine[ring->id].ringbuf;
+	struct intel_context    *ctx = params->request->ctx;
 	u64 exec_start;
 	int instp_mode;
 	u32 instp_mask;
@@ -982,6 +983,12 @@ int intel_execlists_submission(struct i915_execbuffer_params *params,
 
 	trace_i915_gem_ring_dispatch(params->request, params->dispatch_flags);
 
+	if (ring->last_context && ring->last_context != ctx) {
+		intel_lr_context_unpin(ring->last_context, ring);
+		intel_lr_context_pin(ctx, ring);
+		ring->last_context = ctx;
+	}
+
 	i915_gem_execbuffer_move_to_active(vmas, params->request);
 	i915_gem_execbuffer_retire_commands(params);
 
-- 
1.9.1

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