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List:       xen-users
Subject:    [Xen-users] PCI/VGA passthrough and function level reset (FLR)
From:       Robin Axelsson <gu99roax () student ! chalmers ! se>
Date:       2011-12-30 14:12:48
Message-ID: 4EFDC6E0.9030901 () student ! chalmers ! se
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I'm wondering if FLR really must be supported by the PCI card for 
PCI/VGA passthrough to work or if it will work anyway. I have read in 
the VTdHowTo that trying to pass through hardware without the FLR 
feature will result in an error. At the same time I read on a pdf 
document on the VMWare website 
(http://www.vmware.com/files/pdf/techpaper/vsp_4_vmdirectpath_host.pdf) 
that:

-----------------------
Reset Method

Possible values for the reset method include flr, d3d0, link, bridge, or 
default.

The default setting is described as follows. If a device supports 
function level reset (FLR), ESX always uses FLR. If the device does not 
support FLR, ESX next defaults to link reset and bus reset in that 
order. Link reset and bus reset might prevent some devices from being 
assigned to different virtual machines, or from being assigned between 
the VMkernel and virtual machines. In the absence of FLR, it is possible 
to use PCI Power Management capability (D3 to D0 transitions) to trigger 
a reset. Most of the Intel NICs and various other HBAs
support this mode.
-----------------------
So there are other ways of resetting hardware to be used for passthrough 
than the FLR, namely d3d0, link and bridge. Does Xen support any of 
these reset methods? I may want for example to be able to pass through 
an LSI 1068E HBA or an Intel 82572 based NIC to a virtual machine.

Robin.


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