[PATCH v4 5/6] drm/i915: HWSP should be unmapped earlier in LRC teardown sequence

[Dave Gordon <david.s.gordon@intel.com>]

In LRC mode, the HWSP is part of the default context object, and
therefore does not exist independently. Worse, it doesn't contribute
to the refcount on the default context object either.

Currently, the default context is deallocated in intel_lr_context_free(),
but the HWSP kmapping is not torn down until the subsequent call to
intel_logical_ring_cleanup(). Between these calls, ring->status_page.obj
continues to point to the (now non-existent) default context object,
and the kernel mapping likewise points to a page which is now free.

The solution is to dispose of the HWSP kmapping and pointer before the
object itself is freed, so this patch moves the call to the teardown
code from intel_lr_context_free() to intel_logical_ring_cleanup().

This code was introduced in

    48d8238 drm/i915/bdw: Generic logical ring init and cleanup

i.e. it has been there ever since LRC mode was first implemented.

v3:
    Rebased.

Signed-off-by: Dave Gordon <david.s.gordon@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
---
 drivers/gpu/drm/i915/intel_lrc.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index ff38e57..947ef15 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -2003,7 +2003,9 @@ void intel_logical_ring_cleanup(struct intel_engine_cs *ring)
 	i915_cmd_parser_fini_ring(ring);
 	i915_gem_batch_pool_fini(&ring->batch_pool);
 
-	lrc_teardown_hardware_status_page(ring);
+	/* Status page should have gone already */
+	WARN_ON(ring->status_page.page_addr);
+	WARN_ON(ring->status_page.obj);
 
 	ring->disable_lite_restore_wa = false;
 	ring->ctx_desc_template = 0;
@@ -2447,6 +2449,11 @@ void intel_lr_context_free(struct intel_context *ctx)
 			continue;
 
 		if (ctx == ctx->i915->kernel_context) {
+			/*
+			 * The HWSP is part of the kernel context
+			 * object in LRC mode, so tear it down now.
+			 */
+			lrc_teardown_hardware_status_page(ringbuf->ring);
 			intel_unpin_ringbuffer_obj(ringbuf);
 			i915_gem_object_ggtt_unpin(ctx_obj);
 		}
@@ -2517,12 +2524,19 @@ static void lrc_setup_hardware_status_page(struct intel_engine_cs *ring)
 	POSTING_READ(RING_HWS_PGA(ring->mmio_base));
 }
 
+/* This should be called *before* the default context is destroyed */
 static void lrc_teardown_hardware_status_page(struct intel_engine_cs *ring)
 {
-	if (ring->status_page.obj) {
+	struct drm_i915_gem_object *dctx_obj = ring->status_page.obj;
+
+	WARN_ON(!dctx_obj);
+
+	if (ring->status_page.page_addr) {
 		kunmap(kmap_to_page(ring->status_page.page_addr));
-		ring->status_page.obj = NULL;
+		ring->status_page.page_addr = NULL;
 	}
+
+	ring->status_page.obj = NULL;
 }
 
 /**
-- 
1.9.1

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