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Re : [Xen-users] General questions about VGA passthrough

To: Francesco Cat <heartcollector87@xxxxxxxxx>, "xen-users@xxxxxxxxxxxxxxxxxxx" <xen-users@xxxxxxxxxxxxxxxxxxx>

From: David TECHER <davidtecher@xxxxxxxx>

Date: Wed, 12 Oct 2011 22:24:37 +0100 (BST)

Cc:

Delivery-date: Wed, 12 Oct 2011 14:26:15 -0700

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List-id: Xen user discussion <xen-users.lists.xensource.com>

I will answer from my experiment using my nvidia graphic card. The answer may be different for ATI or Intel

> I have a question regarding VGA passthrough.
> If I understood correctly, the only way to have VGA passthrough is hiding the VGA from the Dom0 and giving full control of it to one guest.

Yes

> This means, the guest should just take ownership of the device and start using it (and therefore take control of the screen, too), right?

Yes

> I read that one can dynamically hide PCI devices from the Dom0.

Possible before starting the domU...I never tried to do that while the domU is running.

> What would happen if one did that with a VGA device?
> For example, if I am using linux with an active X server, what is likely to happen?
> In short, would it be possible to "switch" the control of the video card from the Dom0 to the DomU, keeping the Dom0 "alive"
> (IE: no crashes), then giving the VGA control back to the Dom0 after stopping the guest?

Giving control back to dom0 is not possible...Once you stop the domU (safe shutdown), you need to restart the dom0

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