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[Xen-users] PCI/VGA passthrough and function level reset (FLR)



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:

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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.
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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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