APPLIED: [SRU][O][PATCH 0/2] WARNING: CPU: 18 PID: 3683 at arch/powerpc/kvm/../../../virt/kvm/vfio.c Call Traces seen when pci device is detached from the kvm guest (LP: #2104893)

[Mehmet Basaran]

Applied to oracular:linux master-next branch. Thanks.

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Massimiliano Pellizzer <massimiliano.pellizzer at canonical.com> writes:

> BugLink: https://bugs.launchpad.net/bugs/2104893
>
> [Impact]
>
> Currently on book3s-hv, the capability KVM_CAP_SPAPR_TCE_VFIO is only
> available for KVM Guests running on PowerNV and not for the KVM guests
> running on pSeries hypervisors. This prevents a pSeries L2 guest from
> leveraging the in-kernel acceleration for H_PUT_TCE_INDIRECT and
> H_STUFF_TCE hcalls that results in slow startup times for large memory
> guests.
>
> Support for VFIO on pSeries was restored in commit f431a8cde7f1
> ("powerpc/iommu: Reimplement the iommu_table_group_ops for pSeries"),
> making it possible to re-enable this capability on pSeries hosts.
>
> This change enables KVM_CAP_SPAPR_TCE_VFIO for nested PAPR guests on
> pSeries, while maintaining the existing behavior on PowerNV. Booting an
> L2 guest with 128GB of memory shows an average 11% improvement in
> startup time.
>
> [Fix]
>
> Clean cherry pick of:
> - b4392813bbc3b0 KVM: PPC: Enable CAP_SPAPR_TCE_VFIO on pSeries KVM guests
> from linux-next.
>
> [Test Plan]
>
> Tested IBM side using the following procedure:
> 1. Start a guest
> 2. unbind the pci device from host using below command
>
> root at ltcrain8og-lp6:~/NET# virsh nodedev-detach pci_0028_01_00_0
> Device pci_0028_01_00_0 detached
> root at ltcrain8og-lp6:~/NET# virsh nodedev-detach pci_0028_01_00_1
> Device pci_0028_01_00_1 detached
>
> 3. Now attach the pci device to guest using virsh attach-device command. The xml
> snippet used is given below
>
> root at ltcrain8og-lp6:~/NET# vi pci2.xml
> <hostdev mode='subsystem' type='pci' managed='yes'>
>   <source>
>     <address domain='0x0028' bus='0x01' slot='0x00' function='0x0'/>
>   </source>
> </hostdev>
>
> root at ltcrain8og-lp6:~/NET# virsh attach-device vm pci2.xml
> Device attached successfully
>
> 4. On guest side the pci device gets attached sucesfully, and interface comes
> up.
> [root at localhost ~]# lspci
> 0000:00:01.0 Ethernet controller: Red Hat, Inc. Virtio network device
> 0000:00:02.0 SCSI storage controller: Red Hat, Inc. Virtio SCSI
> 0000:00:03.0 USB controller: Red Hat, Inc. QEMU XHCI Host Controller (rev 01)
> 0000:00:04.0 Communication controller: Red Hat, Inc. Virtio console
> 0000:00:05.0 Unclassified device [00ff]: Red Hat, Inc. Virtio memory balloon
> 0000:00:06.0 Unclassified device [00ff]: Red Hat, Inc. Virtio RNG
> 0001:00:01.0 Ethernet controller: Mellanox Technologies MT27710 Family
> [ConnectX-4 Lx]
>
> 5. Now Detach the device using virsh detach command
> root at ltcrain8og-lp6:~/NET# virsh detach-device vm pci2.xml
> Device detached successfully
>
> [Where problems could occur]
>
> The fix affects the KVM subsystem on IBM Power platforms.
> An issue with this fix may lead to incorrect exposure of the
> KVM_CAP_SPAPR_TCE_VFIO capability on hosts or guests
> that do not fully support it.
>
> -- 
> kernel-team mailing list
> kernel-team at lists.ubuntu.com
> https://lists.ubuntu.com/mailman/listinfo/kernel-team
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