linux-kernel - Re: [PATCH v3 1/2] drm/virtio: Add window server support

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Message-ID: <1b7ff044-23c8-1bf7-004e-dd6ea1a7006e@collabora.com>
Date:   Wed, 7 Feb 2018 08:41:47 +0100
From:   Tomeu Vizoso <tomeu.vizoso@...labora.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>,
        Gerd Hoffmann <kraxel@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Zach Reizner <zachr@...gle.com>,
        kernel@...labora.com, dri-devel@...ts.freedesktop.org,
        virtualization@...ts.linux-foundation.org,
        David Airlie <airlied@...ux.ie>,
        Jason Wang <jasowang@...hat.com>,
        Stefan Hajnoczi <stefanha@...il.com>
Subject: Re: [PATCH v3 1/2] drm/virtio: Add window server support

On 02/07/2018 02:09 AM, Michael S. Tsirkin wrote:
> On Tue, Feb 06, 2018 at 03:23:02PM +0100, Gerd Hoffmann wrote:
>>> Creation of shareable buffer by guest
>>> -------------------------------------------------
>>>
>>> 1. Client requests virtio driver to create a buffer suitable for sharing
>>> with host (DRM_VIRTGPU_RESOURCE_CREATE)
>>
>> client or guest proxy?
>>
>>> 4. QEMU maps that buffer to the guest's address space
>>> (KVM_SET_USER_MEMORY_REGION), passes the guest PFN to the virtio driver
>>
>> That part is problematic.  The host can't simply allocate something in
>> the physical address space, because most physical address space
>> management is done by the guest.  All pci bars are mapped by the guest
>> firmware for example (or by the guest OS in case of hotplug).
>>
>>> 4. QEMU pops data+buffers from the virtqueue, looks up shmem FD for each
>>> resource, sends data + FDs to the compositor with SCM_RIGHTS
> 
> If you squint hard, this sounds a bit like a use-case for vhost-user-gpu, does it not?

Can you extend on what makes you think that?

As an aside, crosvm runs the virtio-gpu device in a separate, jailed
process, among other virtual devices.

https://chromium.googlesource.com/chromiumos/platform/crosvm/

Regards,

Tomeu