drm/msm/a6xx: Track current ctx by seqno

In theory a context can be destroyed and a new one allocated at the same
address, making the pointer comparision to detect when we don't need to
update the current pagetables invalid.  Instead assign a sequence number
to each context on creation, and use this for the check.

Fixes: 84c31ee1 ("drm/msm/a6xx: Add support for per-instance pagetables")
Signed-off-by: Rob Clark <robdclark@chromium.org>

drivers/gpu/drm/msm/adreno/a6xx_gpu.c

@@ -106,7 +106,7 @@ static void a6xx_set_pagetable(struct a6xx_gpu *a6xx_gpu,
 	u32 asid;
 	u64 memptr = rbmemptr(ring, ttbr0);
 
-	if (ctx == a6xx_gpu->cur_ctx)
+	if (ctx->seqno == a6xx_gpu->cur_ctx_seqno)
 		return;
 
 	if (msm_iommu_pagetable_params(ctx->aspace->mmu, &ttbr, &asid))
@@ -139,7 +139,7 @@ static void a6xx_set_pagetable(struct a6xx_gpu *a6xx_gpu,
 	OUT_PKT7(ring, CP_EVENT_WRITE, 1);
 	OUT_RING(ring, 0x31);
 
-	a6xx_gpu->cur_ctx = ctx;
+	a6xx_gpu->cur_ctx_seqno = ctx->seqno;
 }
 
 static void a6xx_submit(struct msm_gpu *gpu, struct msm_gem_submit *submit)
@@ -1081,7 +1081,7 @@ static int hw_init(struct msm_gpu *gpu)
 	/* Always come up on rb 0 */
 	a6xx_gpu->cur_ring = gpu->rb[0];
 
-	a6xx_gpu->cur_ctx = NULL;
+	a6xx_gpu->cur_ctx_seqno = 0;
 
 	/* Enable the SQE_to start the CP engine */
 	gpu_write(gpu, REG_A6XX_CP_SQE_CNTL, 1);

drivers/gpu/drm/msm/adreno/a6xx_gpu.h

@@ -19,7 +19,16 @@ struct a6xx_gpu {
 	uint64_t sqe_iova;
 
 	struct msm_ringbuffer *cur_ring;
-	struct msm_file_private *cur_ctx;
+
+	/**
+	 * cur_ctx_seqno:
+	 *
+	 * The ctx->seqno value of the context with current pgtables
+	 * installed.  Tracked by seqno rather than pointer value to
+	 * avoid dangling pointers, and cases where a ctx can be freed
+	 * and a new one created with the same address.
+	 */
+	int cur_ctx_seqno;
 
 	struct a6xx_gmu gmu;
 

drivers/gpu/drm/msm/msm_drv.c

@@ -682,6 +682,7 @@ static void load_gpu(struct drm_device *dev)
 
 static int context_init(struct drm_device *dev, struct drm_file *file)
 {
+	static atomic_t ident = ATOMIC_INIT(0);
 	struct msm_drm_private *priv = dev->dev_private;
 	struct msm_file_private *ctx;
 
@@ -698,6 +699,8 @@ static int context_init(struct drm_device *dev, struct drm_file *file)
 	ctx->aspace = msm_gpu_create_private_address_space(priv->gpu, current);
 	file->driver_priv = ctx;
 
+	ctx->seqno = atomic_inc_return(&ident);
+
 	return 0;
 }
 

drivers/gpu/drm/msm/msm_drv.h

@@ -59,6 +59,7 @@ struct msm_file_private {
 	int queueid;
 	struct msm_gem_address_space *aspace;
 	struct kref ref;
+	int seqno;
 };
 
 enum msm_mdp_plane_property {