[PATCH v6 2/3] drm/i915: Remove extra multi-gt pm-references

[Janusz Krzysztofik <janusz.krzysztofik@xxxxxxxxxxxxxxx>]

There was an attempt to fix an issue of illegal attempts to free a still
active i915 VMA object when parking a GT believed to be idle, reported by
CI on 2-GT Meteor Lake.  As a solution, an extra wakeref for a Primary GT
was acquired from i915_gem_do_execbuffer() -- see commit f56fe3e91787
("drm/i915: Fix a VMA UAF for multi-gt platform").

However, that fix occurred insufficient -- the issue was still reported by
CI.  That wakeref was released on exit from i915_gem_do_execbuffer(), then
potentially before completion of the request and deactivation of its
associated VMAs.  Moreover, CI reports indicated that single-GT platforms
also suffered sporadically from the same race.

Since the issue has now been fixed by a preceding patch "drm/i915/vma: Fix
UAF on destroy against retire race", drop the no longer useful changes
introduced by that insufficient fix.

v3: Also drop the no longer used .wakeref_gt0 field from struct
    i915_execbuffer.
v2: Avoid the word "revert" in commit message (Rodrigo),
  - update commit description reusing relevant chunks dropped from the
    description of the proper fix (Rodrigo).

Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik@xxxxxxxxxxxxxxx>
Cc: Nirmoy Das <nirmoy.das@xxxxxxxxx>
Cc: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
---
 drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c | 18 ------------------
 1 file changed, 18 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
index d3a771afb083e..3f20fe3811999 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
@@ -255,7 +255,6 @@ struct i915_execbuffer {
 	struct intel_context *context; /* logical state for the request */
 	struct i915_gem_context *gem_context; /** caller's context */
 	intel_wakeref_t wakeref;
-	intel_wakeref_t wakeref_gt0;
 
 	/** our requests to build */
 	struct i915_request *requests[MAX_ENGINE_INSTANCE + 1];
@@ -2686,7 +2685,6 @@ static int
 eb_select_engine(struct i915_execbuffer *eb)
 {
 	struct intel_context *ce, *child;
-	struct intel_gt *gt;
 	unsigned int idx;
 	int err;
 
@@ -2710,17 +2708,10 @@ eb_select_engine(struct i915_execbuffer *eb)
 		}
 	}
 	eb->num_batches = ce->parallel.number_children + 1;
-	gt = ce->engine->gt;
 
 	for_each_child(ce, child)
 		intel_context_get(child);
 	eb->wakeref = intel_gt_pm_get(ce->engine->gt);
-	/*
-	 * Keep GT0 active on MTL so that i915_vma_parked() doesn't
-	 * free VMAs while execbuf ioctl is validating VMAs.
-	 */
-	if (gt->info.id)
-		eb->wakeref_gt0 = intel_gt_pm_get(to_gt(gt->i915));
 
 	if (!test_bit(CONTEXT_ALLOC_BIT, &ce->flags)) {
 		err = intel_context_alloc_state(ce);
@@ -2759,9 +2750,6 @@ eb_select_engine(struct i915_execbuffer *eb)
 	return err;
 
 err:
-	if (gt->info.id)
-		intel_gt_pm_put(to_gt(gt->i915), eb->wakeref_gt0);
-
 	intel_gt_pm_put(ce->engine->gt, eb->wakeref);
 	for_each_child(ce, child)
 		intel_context_put(child);
@@ -2775,12 +2763,6 @@ eb_put_engine(struct i915_execbuffer *eb)
 	struct intel_context *child;
 
 	i915_vm_put(eb->context->vm);
-	/*
-	 * This works in conjunction with eb_select_engine() to prevent
-	 * i915_vma_parked() from interfering while execbuf validates vmas.
-	 */
-	if (eb->gt->info.id)
-		intel_gt_pm_put(to_gt(eb->gt->i915), eb->wakeref_gt0);
 	intel_gt_pm_put(eb->context->engine->gt, eb->wakeref);
 	for_each_child(eb->context, child)
 		intel_context_put(child);
-- 
2.43.0