linux-kernel - [PATCH] drm/virtio: Add USE

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Date:   Fri, 18 Feb 2022 07:57:25 -0800
From:   Rob Clark <robdclark@...il.com>
To:     dri-devel@...ts.freedesktop.org
Cc:     Rob Clark <robdclark@...omium.org>,
        David Airlie <airlied@...ux.ie>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Gurchetan Singh <gurchetansingh@...omium.org>,
        Chia-I Wu <olvaffe@...il.com>, Daniel Vetter <daniel@...ll.ch>,
        virtualization@...ts.linux-foundation.org (open list:VIRTIO GPU DRIVER),
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH] drm/virtio: Add USE_INTERNAL blob flag

From: Rob Clark <robdclark@...omium.org>

With native userspace drivers in guest, a lot of GEM objects need to be
neither shared nor mappable.  And in fact making everything mappable
and/or sharable results in unreasonably high fd usage in host VMM.

Signed-off-by: Rob Clark <robdclark@...omium.org>
---
This is for a thing I'm working on, a new virtgpu context type that
allows for running native userspace driver in the guest, with a
thin shim in the host VMM.  In this case, the guest has a lot of
GEM buffer objects which need to be neither shared nor mappable.

Alternative idea is to just drop the restriction that blob_flags
be non-zero.  I'm ok with either approach.

 drivers/gpu/drm/virtio/virtgpu_ioctl.c | 7 ++++++-
 include/uapi/drm/virtgpu_drm.h         | 1 +
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/virtio/virtgpu_ioctl.c b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
index 69f1952f3144..92e1ba6b8078 100644
--- a/drivers/gpu/drm/virtio/virtgpu_ioctl.c
+++ b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
@@ -36,7 +36,8 @@
 
 #define VIRTGPU_BLOB_FLAG_USE_MASK (VIRTGPU_BLOB_FLAG_USE_MAPPABLE | \
 				    VIRTGPU_BLOB_FLAG_USE_SHAREABLE | \
-				    VIRTGPU_BLOB_FLAG_USE_CROSS_DEVICE)
+				    VIRTGPU_BLOB_FLAG_USE_CROSS_DEVICE | \
+				    VIRTGPU_BLOB_FLAG_USE_INTERNAL)
 
 static int virtio_gpu_fence_event_create(struct drm_device *dev,
 					 struct drm_file *file,
@@ -662,6 +663,10 @@ static int verify_blob(struct virtio_gpu_device *vgdev,
 	params->size = rc_blob->size;
 	params->blob = true;
 	params->blob_flags = rc_blob->blob_flags;
+
+	/* USE_INTERNAL is local to guest kernel, don't past to host: */
+	params->blob_flags &= ~VIRTGPU_BLOB_FLAG_USE_INTERNAL;
+
 	return 0;
 }
 
diff --git a/include/uapi/drm/virtgpu_drm.h b/include/uapi/drm/virtgpu_drm.h
index 0512fde5e697..62b7483e5c60 100644
--- a/include/uapi/drm/virtgpu_drm.h
+++ b/include/uapi/drm/virtgpu_drm.h
@@ -163,6 +163,7 @@ struct drm_virtgpu_resource_create_blob {
 #define VIRTGPU_BLOB_FLAG_USE_MAPPABLE     0x0001
 #define VIRTGPU_BLOB_FLAG_USE_SHAREABLE    0x0002
 #define VIRTGPU_BLOB_FLAG_USE_CROSS_DEVICE 0x0004
+#define VIRTGPU_BLOB_FLAG_USE_INTERNAL     0x0008   /* not-mappable, not-shareable */
 	/* zero is invalid blob_mem */
 	__u32 blob_mem;
 	__u32 blob_flags;
-- 
2.34.1