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Date:   Wed,  9 Mar 2022 16:52:15 +0000
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Subject: [RFC v3 5/8] dmabuf: Add gpu cgroup charge transfer function
From:   "T.J. Mercier" <tjmercier@google.com>
To:     Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Jonathan Corbet <corbet@lwn.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "=?UTF-8?q?Arve=20Hj=C3=B8nnev=C3=A5g?=" <arve@android.com>,
        Todd Kjos <tkjos@android.com>,
        Martijn Coenen <maco@android.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        Christian Brauner <brauner@kernel.org>,
        Hridya Valsaraju <hridya@google.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Sumit Semwal <sumit.semwal@linaro.org>,
        "=?UTF-8?q?Christian=20K=C3=B6nig?=" <christian.koenig@amd.com>,
        Benjamin Gaignard <benjamin.gaignard@linaro.org>,
        Liam Mark <lmark@codeaurora.org>,
        Laura Abbott <labbott@redhat.com>,
        Brian Starkey <Brian.Starkey@arm.com>,
        John Stultz <john.stultz@linaro.org>,
        Tejun Heo <tj@kernel.org>, Zefan Li <lizefan.x@bytedance.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Shuah Khan <shuah@kernel.org>
Cc:     kaleshsingh@google.com, Kenny.Ho@amd.com,
        "T.J. Mercier" <tjmercier@google.com>,
        dri-devel@lists.freedesktop.org, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-media@vger.kernel.org,
        linaro-mm-sig@lists.linaro.org, cgroups@vger.kernel.org,
        linux-kselftest@vger.kernel.org
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From: Hridya Valsaraju <hridya@google.com>

The dma_buf_charge_transfer function provides a way for processes to
transfer charge of a buffer to a different process. This is essential
for the cases where a central allocator process does allocations for
various subsystems, hands over the fd to the client who requested the
memory and drops all references to the allocated memory.

Signed-off-by: Hridya Valsaraju <hridya@google.com>
Signed-off-by: T.J. Mercier <tjmercier@google.com>

---
v3 changes
Use more common dual author commit message format per John Stultz.

v2 changes
Move dma-buf cgroup charge transfer from a dma_buf_op defined by every
heap to a single dma-buf function for all heaps per Daniel Vetter and
Christian K=C3=B6nig.
---
 drivers/dma-buf/dma-buf.c | 48 +++++++++++++++++++++++++++++++++++++++
 include/linux/dma-buf.h   |  2 ++
 2 files changed, 50 insertions(+)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 83d0d1b91547..55e1b982f840 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -1374,6 +1374,54 @@ void dma_buf_vunmap(struct dma_buf *dmabuf, struct d=
ma_buf_map *map)
 }
 EXPORT_SYMBOL_NS_GPL(dma_buf_vunmap, DMA_BUF);
=20
+/**
+ * dma_buf_charge_transfer - Change the GPU cgroup to which the provided d=
ma_buf
+ * is charged.
+ * @dmabuf:	[in]	buffer whose charge will be migrated to a different GPU
+ *			cgroup
+ * @gpucg:	[in]	the destination GPU cgroup for dmabuf's charge
+ *
+ * Only tasks that belong to the same cgroup the buffer is currently charg=
ed to
+ * may call this function, otherwise it will return -EPERM.
+ *
+ * Returns 0 on success, or a negative errno code otherwise.
+ */
+int dma_buf_charge_transfer(struct dma_buf *dmabuf, struct gpucg *gpucg)
+{
+#ifdef CONFIG_CGROUP_GPU
+	struct gpucg *current_gpucg;
+	int ret =3D 0;
+
+	/*
+	 * Verify that the cgroup of the process requesting the transfer is the
+	 * same as the one the buffer is currently charged to.
+	 */
+	current_gpucg =3D gpucg_get(current);
+	mutex_lock(&dmabuf->lock);
+	if (current_gpucg !=3D dmabuf->gpucg) {
+		ret =3D -EPERM;
+		goto err;
+	}
+
+	ret =3D gpucg_try_charge(gpucg, dmabuf->gpucg_dev, dmabuf->size);
+	if (ret)
+		goto err;
+
+	dmabuf->gpucg =3D gpucg;
+
+	/* uncharge the buffer from the cgroup it's currently charged to. */
+	gpucg_uncharge(current_gpucg, dmabuf->gpucg_dev, dmabuf->size);
+
+err:
+	mutex_unlock(&dmabuf->lock);
+	gpucg_put(current_gpucg);
+	return ret;
+#else
+	return 0;
+#endif /* CONFIG_CGROUP_GPU */
+}
+EXPORT_SYMBOL_NS_GPL(dma_buf_charge_transfer, DMA_BUF);
+
 #ifdef CONFIG_DEBUG_FS
 static int dma_buf_debug_show(struct seq_file *s, void *unused)
 {
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index 742f29c3daaf..85c940c08867 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -646,4 +646,6 @@ int dma_buf_mmap(struct dma_buf *, struct vm_area_struc=
t *,
 		 unsigned long);
 int dma_buf_vmap(struct dma_buf *dmabuf, struct dma_buf_map *map);
 void dma_buf_vunmap(struct dma_buf *dmabuf, struct dma_buf_map *map);
+
+int dma_buf_charge_transfer(struct dma_buf *dmabuf, struct gpucg *gpucg);
 #endif /* __DMA_BUF_H__ */
--=20
2.35.1.616.g0bdcbb4464-goog