linux-kernel - [PATCH v2 4/4] drm/virtio: Add memory barriers for capset cache.

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Message-Id: <20190610211810.253227-5-davidriley@chromium.org>
Date:   Mon, 10 Jun 2019 14:18:10 -0700
From:   davidriley@...omium.org
To:     Gerd Hoffmann <kraxel@...hat.com>, dri-devel@...ts.freedesktop.org,
        virtualization@...ts.linux-foundation.org
Cc:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        linux-kernel@...r.kernel.org, David Riley <davidriley@...omium.org>
Subject: [PATCH v2 4/4] drm/virtio: Add memory barriers for capset cache.

From: David Riley <davidriley@...omium.org>

After data is copied to the cache entry, atomic_set is used indicate
that the data is the entry is valid without appropriate memory barriers.
Similarly the read side was missing the corresponding memory barriers.

Signed-off-by: David Riley <davidriley@...omium.org>
---
 drivers/gpu/drm/virtio/virtgpu_ioctl.c | 3 +++
 drivers/gpu/drm/virtio/virtgpu_vq.c    | 2 ++
 2 files changed, 5 insertions(+)

diff --git a/drivers/gpu/drm/virtio/virtgpu_ioctl.c b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
index 88c1ed57a3c5..a50495083d6f 100644
--- a/drivers/gpu/drm/virtio/virtgpu_ioctl.c
+++ b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
@@ -542,6 +542,9 @@ static int virtio_gpu_get_caps_ioctl(struct drm_device *dev,
 	if (!ret)
 		return -EBUSY;
 
+	/* is_valid check must proceed before copy of the cache entry. */
+	smp_rmb();
+
 	ptr = cache_ent->caps_cache;
 
 	if (copy_to_user((void __user *)(unsigned long)args->addr, ptr, size))
diff --git a/drivers/gpu/drm/virtio/virtgpu_vq.c b/drivers/gpu/drm/virtio/virtgpu_vq.c
index dd5ead2541c2..c7a5ca027245 100644
--- a/drivers/gpu/drm/virtio/virtgpu_vq.c
+++ b/drivers/gpu/drm/virtio/virtgpu_vq.c
@@ -583,6 +583,8 @@ static void virtio_gpu_cmd_capset_cb(struct virtio_gpu_device *vgdev,
 		    cache_ent->id == le32_to_cpu(cmd->capset_id)) {
 			memcpy(cache_ent->caps_cache, resp->capset_data,
 			       cache_ent->size);
+			/* Copy must occur before is_valid is signalled. */
+			smp_wmb();
 			atomic_set(&cache_ent->is_valid, 1);
 			break;
 		}
-- 
2.22.0.rc2.383.gf4fbbf30c2-goog