[vfio-users] Is stolen memory wasted after IGD passed through into guest os?

[Alex Williamson]

On Tue, 25 Sep 2018 09:44:24 +0800
Acewind <acewind at gmail.com> wrote:

> In my host os, command of ' lspci -v -s 00:02.0' will show:
> Memory at e8000000 (64-bit, prefetchable) [size=128M]
> 
> Is this 128M memory called 'stolen memory'?

No, stolen memory is system memory dedicated to graphics use, it is not
represented by a PCI BAR.
 
> If this IGD device is passed through into guest os, will it be deserted and
> wasted? Or mapped into and resused in guest os?

PCI BARs are mapped to the VM.  SeaBIOS will attempt to allocate new
stolen memory in the VM, so the host stolen memory is wasted, but it's
not represented in a BAR.  Re-using the host stolen memory is difficult
because it's not actually a resource associated with the device except
through IGD usage and it's physical address space is immovable,
creating holes in the VM address space at host specific addresses. 
Thanks,

Alex