drm/vmwgfx: Update last_read_seqno under the fence lock

There was a possible race in vmw_update_seqno. Because of this race it
was possible for last_read_seqno to go backwards. Remove this function
and replace it with vmw_update_fences which now sets and returns the
last_read_seqno while holding the fence lock. This serialization via the
fence lock ensures that last_read_seqno is monotonic again.

Signed-off-by: Ian Forbes <ian.forbes@broadcom.com>
Signed-off-by: Zack Rusin <zack.rusin@broadcom.com>
Link: https://lore.kernel.org/r/20250530183510.733175-1-ian.forbes@broadcom.com

7 files changed, 22 insertions, 31 deletions

diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_cmd.c b/drivers/gpu/drm/vmwgfx/vmwgfx_cmd.c
index dd4ca6a9c690..8fe02131a6c4 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_cmd.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_cmd.c
@@ -544,7 +544,7 @@ int vmw_cmd_send_fence(struct vmw_private *dev_priv, uint32_t *seqno)
 	cmd_fence = (struct svga_fifo_cmd_fence *) fm;
 	cmd_fence->fence = *seqno;
 	vmw_cmd_commit_flush(dev_priv, bytes);
-	vmw_update_seqno(dev_priv);
+	vmw_fences_update(dev_priv->fman);
 
 out_err:
 	return ret;
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c b/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c
index 37b832e552a4..bc0342c58b4b 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c
@@ -440,8 +440,10 @@ static int vmw_device_init(struct vmw_private *dev_priv)
 		vmw_write(dev_priv, SVGA_REG_CONFIG_DONE, 1);
 	}
 
-	dev_priv->last_read_seqno = vmw_fence_read(dev_priv);
-	atomic_set(&dev_priv->marker_seq, dev_priv->last_read_seqno);
+	u32 seqno = vmw_fence_read(dev_priv);
+
+	atomic_set(&dev_priv->last_read_seqno, seqno);
+	atomic_set(&dev_priv->marker_seq, seqno);
 	return 0;
 }
 
@@ -454,7 +456,7 @@ static void vmw_device_fini(struct vmw_private *vmw)
 	while (vmw_read(vmw, SVGA_REG_BUSY) != 0)
 		;
 
-	vmw->last_read_seqno = vmw_fence_read(vmw);
+	atomic_set(&vmw->last_read_seqno, vmw_fence_read(vmw));
 
 	vmw_write(vmw, SVGA_REG_CONFIG_DONE,
 		  vmw->config_done_state);
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_drv.h b/drivers/gpu/drm/vmwgfx/vmwgfx_drv.h
index 594af8eb04c6..19565e4aa59c 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_drv.h
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_drv.h
@@ -522,7 +522,7 @@ struct vmw_private {
 	int cmdbuf_waiters; /* Protected by waiter_lock */
 	int error_waiters; /* Protected by waiter_lock */
 	int fifo_queue_waiters; /* Protected by waiter_lock */
-	uint32_t last_read_seqno;
+	atomic_t last_read_seqno;
 	struct vmw_fence_manager *fman;
 	uint32_t irq_mask; /* Updates protected by waiter_lock */
 
@@ -1006,7 +1006,6 @@ extern int vmw_fallback_wait(struct vmw_private *dev_priv,
 			     uint32_t seqno,
 			     bool interruptible,
 			     unsigned long timeout);
-extern void vmw_update_seqno(struct vmw_private *dev_priv);
 extern void vmw_seqno_waiter_add(struct vmw_private *dev_priv);
 extern void vmw_seqno_waiter_remove(struct vmw_private *dev_priv);
 extern void vmw_goal_waiter_add(struct vmw_private *dev_priv);
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c b/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c
index e831e324e737..90ce5372343b 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c
@@ -3878,8 +3878,7 @@ vmw_execbuf_copy_fence_user(struct vmw_private *dev_priv,
 
 		fence_rep.handle = fence_handle;
 		fence_rep.seqno = fence->base.seqno;
-		vmw_update_seqno(dev_priv);
-		fence_rep.passed_seqno = dev_priv->last_read_seqno;
+		fence_rep.passed_seqno = vmw_fences_update(dev_priv->fman);
 	}
 
 	/*
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_fence.c b/drivers/gpu/drm/vmwgfx/vmwgfx_fence.c
index 588d50ababf6..136f6b816795 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_fence.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_fence.c
@@ -172,7 +172,7 @@ vmwgfx_wait_cb(struct dma_fence *fence, struct dma_fence_cb *cb)
 	wake_up_process(wait->task);
 }
 
-static void __vmw_fences_update(struct vmw_fence_manager *fman);
+static u32 __vmw_fences_update(struct vmw_fence_manager *fman);
 
 static long vmw_fence_wait(struct dma_fence *f, bool intr, signed long timeout)
 {
@@ -457,7 +457,7 @@ static bool vmw_fence_goal_check_locked(struct vmw_fence_obj *fence)
 	return true;
 }
 
-static void __vmw_fences_update(struct vmw_fence_manager *fman)
+static u32 __vmw_fences_update(struct vmw_fence_manager *fman)
 {
 	struct vmw_fence_obj *fence, *next_fence;
 	struct list_head action_list;
@@ -495,13 +495,17 @@ rerun:
 
 	if (!list_empty(&fman->cleanup_list))
 		(void) schedule_work(&fman->work);
+	atomic_set_release(&fman->dev_priv->last_read_seqno, seqno);
+	return seqno;
 }
 
-void vmw_fences_update(struct vmw_fence_manager *fman)
+u32 vmw_fences_update(struct vmw_fence_manager *fman)
 {
+	u32 seqno;
 	spin_lock(&fman->lock);
-	__vmw_fences_update(fman);
+	seqno = __vmw_fences_update(fman);
 	spin_unlock(&fman->lock);
+	return seqno;
 }
 
 bool vmw_fence_obj_signaled(struct vmw_fence_obj *fence)
@@ -778,7 +782,6 @@ int vmw_fence_obj_signaled_ioctl(struct drm_device *dev, void *data,
 		(struct drm_vmw_fence_signaled_arg *) data;
 	struct ttm_base_object *base;
 	struct vmw_fence_obj *fence;
-	struct vmw_fence_manager *fman;
 	struct ttm_object_file *tfile = vmw_fpriv(file_priv)->tfile;
 	struct vmw_private *dev_priv = vmw_priv(dev);
 
@@ -787,14 +790,11 @@ int vmw_fence_obj_signaled_ioctl(struct drm_device *dev, void *data,
 		return PTR_ERR(base);
 
 	fence = &(container_of(base, struct vmw_user_fence, base)->fence);
-	fman = fman_from_fence(fence);
 
 	arg->signaled = vmw_fence_obj_signaled(fence);
 
 	arg->signaled_flags = arg->flags;
-	spin_lock(&fman->lock);
-	arg->passed_seqno = dev_priv->last_read_seqno;
-	spin_unlock(&fman->lock);
+	arg->passed_seqno = atomic_read_acquire(&dev_priv->last_read_seqno);
 
 	ttm_base_object_unref(&base);
 
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_fence.h b/drivers/gpu/drm/vmwgfx/vmwgfx_fence.h
index a7eee579c76a..10264dab5f6a 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_fence.h
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_fence.h
@@ -86,7 +86,7 @@ vmw_fence_obj_reference(struct vmw_fence_obj *fence)
 	return fence;
 }
 
-extern void vmw_fences_update(struct vmw_fence_manager *fman);
+u32 vmw_fences_update(struct vmw_fence_manager *fman);
 
 extern bool vmw_fence_obj_signaled(struct vmw_fence_obj *fence);
 
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_irq.c b/drivers/gpu/drm/vmwgfx/vmwgfx_irq.c
index 086e69a130d4..592cd78e10e0 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_irq.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_irq.c
@@ -123,26 +123,17 @@ static bool vmw_fifo_idle(struct vmw_private *dev_priv, uint32_t seqno)
 	return (vmw_read(dev_priv, SVGA_REG_BUSY) == 0);
 }
 
-void vmw_update_seqno(struct vmw_private *dev_priv)
-{
-	uint32_t seqno = vmw_fence_read(dev_priv);
-
-	if (dev_priv->last_read_seqno != seqno) {
-		dev_priv->last_read_seqno = seqno;
-		vmw_fences_update(dev_priv->fman);
-	}
-}
-
 bool vmw_seqno_passed(struct vmw_private *dev_priv,
 			 uint32_t seqno)
 {
 	bool ret;
+	u32 last_read_seqno = atomic_read_acquire(&dev_priv->last_read_seqno);
 
-	if (likely(dev_priv->last_read_seqno - seqno < VMW_FENCE_WRAP))
+	if (last_read_seqno - seqno < VMW_FENCE_WRAP)
 		return true;
 
-	vmw_update_seqno(dev_priv);
-	if (likely(dev_priv->last_read_seqno - seqno < VMW_FENCE_WRAP))
+	last_read_seqno = vmw_fences_update(dev_priv->fman);
+	if (last_read_seqno - seqno < VMW_FENCE_WRAP)
 		return true;
 
 	if (!vmw_has_fences(dev_priv) && vmw_fifo_idle(dev_priv, seqno))