[Xen-bugs] [Bug 1742] Passthrough VF does not work after DomU reboot

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http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=1742





------- Comment #5 from jason.kwon@xxxxxxxxxxxx  2011-02-15 19:09 -------
Steps to reproduce issue:

Case 1 (VF passthrough functionality fails with IOMMU page faults):
1) Boot Xen on hardware, with iommu=verbose.
2) Boot DomU with VF passthrough.  Select original DomU distro kernel (in my
case, 2.6.35-22-server).  Observe MSI warning messages in 'xm dmesg.'
3) Configure VF in guest, verify that network is functional.
4) Shut down guest.
5) Boot DomU again, this time selecting a _different_ kernel (in my case,
2.6.35-23-server).
6) Configure VF in guest, and attempt to access network.  Network will not be
functional.  Observe IOMMU page fault messages in 'xm dmesg.'

The xen-dmesg file attached to this bug follows Case 1.  For step 5, I tried
many different kernels, and none worked except for the kernel that was
originally installed with the distro.  I also tried a RedHat guest and observed
the same thing--only the 2.6.18 kernel installed at guest creation gave a
functional VF, any other kernel did not allow VF network traffic.

Case 2 (VF passthrough functionality fails silently):
1) Boot Xen on hardware, with iommu=verbose.
2) Boot DomU with VF passthrough.  Select kernel _other than_ original distro
kernel (in my case, 2.6.35-23-server).  Observe that there are _no_ MSI warning
messages in 'xm dmesg.'
3) Configure VF in guest, and attempt to access network.  Network will not be
functional.  Observe that there are _no_ IOMMU page fault messages in 'xm
dmesg.'

Case 3 (MSI warnings appear only in first boot of guest):
1) Boot Xen on hardware, with iommu=verbose.
2) Boot DomU with VF passthrough.  Select original DomU distro kernel (in my
case, 2.6.35-22-server).  Observe MSI warning messages in 'xm dmesg.'
3) Configure VF in guest, verify that network is functional.
4) Shut down guest.
5) Boot DomU again, booting the original DomU distro kernel again (in my case,
2.6.35-22-server).  Observe that there are _no_ new MSI warning messages in 'xm
dmesg.'

Case 3 is not strictly a 'failure' case, but it does illustrate a difference in
behavior between boots of the same guest.


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