17.06.2019 16:33, Hans Verkuil пишет:

On 6/2/19 11:37 PM, Dmitry Osipenko wrote:

quoted

Frequent IOMMU remappings take about 50% of CPU usage because there is
quite a lot to remap. Defer dmabuf's unmapping by 5 seconds in order to
mitigate the mapping overhead which goes away completely and driver works
as fast as in a case of a disabled IOMMU. The case of a disabled IOMMU
should also benefit a tad from the caching since CPU cache maintenance
that happens on dmabuf's attaching takes some resources.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
---
 drivers/staging/media/tegra-vde/Makefile      |   2 +-
 .../staging/media/tegra-vde/dmabuf-cache.c    | 223 ++++++++++++++++++
 drivers/staging/media/tegra-vde/iommu.c       |   2 -
 drivers/staging/media/tegra-vde/vde.c         | 143 +++--------
 drivers/staging/media/tegra-vde/vde.h         |  18 +-
 5 files changed, 273 insertions(+), 115 deletions(-)
 create mode 100644 drivers/staging/media/tegra-vde/dmabuf-cache.c

diff --git a/drivers/staging/media/tegra-vde/Makefile b/drivers/staging/media/tegra-vde/Makefile
index c11867e28233..2827f7601de8 100644
--- a/drivers/staging/media/tegra-vde/Makefile
+++ b/drivers/staging/media/tegra-vde/Makefile

@@ -1,3 +1,3 @@
 # SPDX-License-Identifier: GPL-2.0
-tegra-vde-y := vde.o iommu.o
+tegra-vde-y := vde.o iommu.o dmabuf-cache.o
 obj-$(CONFIG_TEGRA_VDE)	+= tegra-vde.o

diff --git a/drivers/staging/media/tegra-vde/dmabuf-cache.c b/drivers/staging/media/tegra-vde/dmabuf-cache.c
new file mode 100644
index 000000000000..fcde8d1c37e7
--- /dev/null
+++ b/drivers/staging/media/tegra-vde/dmabuf-cache.c

@@ -0,0 +1,223 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * NVIDIA Tegra Video decoder driver
+ *
+ * Copyright (C) 2016-2019 GRATE-DRIVER project
+ */
+
+#include <linux/dma-buf.h>
+#include <linux/iova.h>
+#include <linux/kernel.h>
+#include <linux/list.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/workqueue.h>
+
+#include "vde.h"
+
+struct tegra_vde_cache_entry {
+	enum dma_data_direction dma_dir;
+	struct dma_buf_attachment *a;
+	struct delayed_work dwork;
+	struct tegra_vde *vde;
+	struct list_head list;
+	struct sg_table *sgt;
+	struct iova *iova;
+	unsigned int refcnt;
+};
+
+static void tegra_vde_release_entry(struct tegra_vde_cache_entry *entry)
+{
+	struct dma_buf *dmabuf = entry->a->dmabuf;
+
+	WARN_ON_ONCE(entry->refcnt);
+
+	if (entry->vde->domain)
+		tegra_vde_iommu_unmap(entry->vde, entry->iova);
+
+	dma_buf_unmap_attachment(entry->a, entry->sgt, entry->dma_dir);
+	dma_buf_detach(dmabuf, entry->a);
+	dma_buf_put(dmabuf);
+
+	list_del(&entry->list);
+	kfree(entry);
+}
+
+static void tegra_vde_delayed_unmap(struct work_struct *work)
+{
+	struct tegra_vde_cache_entry *entry;
+
+	entry = container_of(work, struct tegra_vde_cache_entry,
+			     dwork.work);
+
+	mutex_lock(&entry->vde->map_lock);
+	tegra_vde_release_entry(entry);
+	mutex_unlock(&entry->vde->map_lock);

From smatch:

drivers/staging/media/tegra-vde/dmabuf-cache.c:55 tegra_vde_delayed_unmap() error: dereferencing freed memory 'entry'

That's a very good catch, thanks you very much! I'm keep forgetting about smatch, it's
a useful tool. And unfortunately I can't KASAN the driver because ARM32 doesn't
support KASAN in upstream and Xorg hangs with the unofficial patch that adds support
for the KASAN.

[snip]

quoted

+	entry->dma_dir = dma_dir;
+	entry->iova = iova;

From smatch:

drivers/staging/media/tegra-vde/dmabuf-cache.c:133 tegra_vde_dmabuf_cache_map() error: uninitialized symbol 'iova'.

This is fine, but indeed won't hurt to explicitly initialize to NULL.

Thanks again!