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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Gerd Hoffmann <kraxel@redhat.com>,
        Dave Airlie <airlied@redhat.com>
Subject: [PATCH 5.0 117/117] drm/virtio: do NOT reuse resource ids
Date:   Mon, 15 Apr 2019 21:01:27 +0200
Message-Id: <20190415183750.700572385@linuxfoundation.org>
In-Reply-To: <20190415183744.887851196@linuxfoundation.org>
References: <20190415183744.887851196@linuxfoundation.org>
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From: Gerd Hoffmann <kraxel@redhat.com>

commit 16065fcdd19ddb9e093192914ac863884f308766 upstream.

Bisected guest kernel changes crashing qemu.  Landed at
"6c1cd97bda drm/virtio: fix resource id handling".  Looked again, and
noticed we where not only leaking *some* ids, but *all* ids.  The old
code never ever called virtio_gpu_resource_id_put().

So, commit 6c1cd97bda effectively makes the linux kernel starting
re-using IDs after releasing them, and apparently virglrenderer can't
deal with that.  Oops.

This patch puts a temporary stopgap into place for the 5.0 release.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190208140409.15280-1-kraxel@redhat.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/gpu/drm/virtio/virtgpu_object.c |   13 +++++++++++++
 1 file changed, 13 insertions(+)

--- a/drivers/gpu/drm/virtio/virtgpu_object.c
+++ b/drivers/gpu/drm/virtio/virtgpu_object.c
@@ -28,10 +28,21 @@
 static int virtio_gpu_resource_id_get(struct virtio_gpu_device *vgdev,
 				       uint32_t *resid)
 {
+#if 0
 	int handle = ida_alloc(&vgdev->resource_ida, GFP_KERNEL);
 
 	if (handle < 0)
 		return handle;
+#else
+	static int handle;
+
+	/*
+	 * FIXME: dirty hack to avoid re-using IDs, virglrenderer
+	 * can't deal with that.  Needs fixing in virglrenderer, also
+	 * should figure a better way to handle that in the guest.
+	 */
+	handle++;
+#endif
 
 	*resid = handle + 1;
 	return 0;
@@ -39,7 +50,9 @@ static int virtio_gpu_resource_id_get(st
 
 static void virtio_gpu_resource_id_put(struct virtio_gpu_device *vgdev, uint32_t id)
 {
+#if 0
 	ida_free(&vgdev->resource_ida, id - 1);
+#endif
 }
 
 static void virtio_gpu_ttm_bo_destroy(struct ttm_buffer_object *tbo)