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[Xen-devel] PCI Passthrough and PV-OPS

To: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: [Xen-devel] PCI Passthrough and PV-OPS
From: "Kinsella, Ray" <ray.kinsella@xxxxxxxxx>
Date: Thu, 3 Mar 2011 14:25:47 +0000
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Thread-topic: PCI Passthrough and PV-OPS

Hi all,


I am having a problem with Xen 4.0.1, PCI Passthrough with VT-d and Linux PV Guests, and I was wondering if anyone else had seen it.

In both Dom 0 and Dom U’s I am using 64bit PV-OPS Kernels from Jeremy Fitzhartridge’s Git repo.


I am using dual port SR-IOV NIC’s to test, passing through physical functions only.

Passthrough appears to work, I can passthrough the NIC and it will appear in the guest with lspci.

The guest detects the new device and loads the driver to service the NIC, as you would expect.


The guest is complaining about the NIC being hung, the message “Detected Tx Unit Hang...” is appearing in the system log on the guest.

In the Xen log, VT-d is producing errors similar to this one;


(XEN) [VT-D]iommu.c:824: iommu_fault_status: Primary Pending Fault

(XEN) [VT-D]iommu.c:799: DMAR:[DMA Read] Request device [03:00.0] fault addr 7c584000, iommu reg = ffff82c3fff57000

(XEN) DMAR:[fault reason 06h] PTE Read access is not set

(XEN) print_vtd_entries: iommu = ffff83016fffa5f0 bdf = 3:0.0 gmfn = 7c584

(XEN)     root_entry = ffff83016ff38000

(XEN)     root_entry[3] = 14d90a001

(XEN)     context = ffff83014d90a000

(XEN)     context[0] = 102_152209005

(XEN)     l4 = ffff830152209000

(XEN)     l4_index = 0

(XEN)     l4[0] = 152208003

(XEN)     l3 = ffff830152208000

(XEN)     l3_index = 1

(XEN)     l3[1] = 0

(XEN)     l3[1] not present


My understanding of what is happening here is that page table mappings are missing from VT-d’s page table, mapping machine physical addresses to my PV guest’s physical addresses. I have had a look at iommu_populate_page_table and I dumped the mappings as they are being setup but couldn’t see a mapping for the GPA 0x7c584000 above?


Has anyone else encountered this issue?




Ray Kinsella

Intel Shannon Limited
Registered in Ireland
Registered Office: Collinstown Industrial Park, Leixlip, County Kildare
Registered Number: 308263
Business address: Dromore House, East Park, Shannon, Co. Clare

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