linux-kernel - [PATCH] drm/msm/a6xx: Track current ctx by seqno

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Message-Id: <20210930182506.1236811-1-robdclark@gmail.com>
Date:   Thu, 30 Sep 2021 11:25:02 -0700
From:   Rob Clark <robdclark@...il.com>
To:     dri-devel@...ts.freedesktop.org
Cc:     freedreno@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        Jordan Crouse <jordan@...micpenguin.net>,
        Rob Clark <robdclark@...omium.org>,
        Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Akhil P Oommen <akhilpo@...eaurora.org>,
        Jonathan Marek <jonathan@...ek.ca>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Sharat Masetty <smasetty@...eaurora.org>,
        Douglas Anderson <dianders@...omium.org>,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        Yangtao Li <tiny.windzz@...il.com>,
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH] drm/msm/a6xx: Track current ctx by seqno

From: Rob Clark <robdclark@...omium.org>

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: 84c31ee16f90 ("drm/msm/a6xx: Add support for per-instance pagetables")
Signed-off-by: Rob Clark <robdclark@...omium.org>
---
 drivers/gpu/drm/msm/adreno/a6xx_gpu.c |  6 +++---
 drivers/gpu/drm/msm/adreno/a6xx_gpu.h | 11 ++++++++++-
 drivers/gpu/drm/msm/msm_drv.c         |  3 +++
 drivers/gpu/drm/msm/msm_drv.h         |  1 +
 4 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
index 5e1ae3df42ba..e0a8b2fd1ff0 100644
--- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
+++ b/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);
diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.h b/drivers/gpu/drm/msm/adreno/a6xx_gpu.h
index 0bc2d062f54a..8e5527c881b1 100644
--- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.h
+++ b/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;
 
diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
index 624078b3adf2..30c1efc3d8a0 100644
--- a/drivers/gpu/drm/msm/msm_drv.c
+++ b/drivers/gpu/drm/msm/msm_drv.c
@@ -711,6 +711,7 @@ 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;
 
@@ -727,6 +728,8 @@ 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;
 }
 
diff --git a/drivers/gpu/drm/msm/msm_drv.h b/drivers/gpu/drm/msm/msm_drv.h
index de062450add4..8633d0059a3e 100644
--- a/drivers/gpu/drm/msm/msm_drv.h
+++ b/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 {
-- 
2.31.1