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Re: [Xen-devel] dom0/pvh: Dom0 PVH with PCI passthrough support status

On Tue, Oct 30, 2018 at 01:32:38PM +0200, Alexandru Vasile wrote:
> Hello,
> > There is some low-hanging fruit, both in Xen and the Linux kernel,
> > which can really be worked in parallel by different parties, so let me
> > know if you have some capacity and we can speak about sharing the
> > workload.
> Could you share more details about the low-hanging fruit?
> Following with an update, I managed to start a PVH Dom0 with the patches
> from Roger’s fixes branch 
> http://xenbits.xen.org/gitweb/?p=people/royger/xen.git;a=shortlog;h=refs/heads/fixes-pvh-v2
> and with the xen kernel tip
> https://kernel.googlesource.com/pub/scm/linux/kernel/git/xen/tip/ (a978a5b –
> latest commit).
> When trying to PCI passthrough a NIC to a HVM DomU guest from PVH Dom0, the
> host completely freezes and reboots and xl returns the following errors:
> libxl: error:libxl_qmp.c:334:qmp_handle_error_reponse: Domain 1:received an
> error message from QMP server: Mapping machine irq 16 to pirq -1 failed:
> Function not implemented
> libxl: error:libxl_pci.c:1300:libxl__add_pcidevs: Domain
> 1:libxl_device_pci_add failed: -3
> libxl: error:libxl_create.c:1522:domcreate_attach_devices: Domain 1:unable
> to add pci devices
> Is someone familiar with this problem or the next steps needed in order to
> make it work properly?

I'm afraid you are likely the first to attempt PCI passthrough from a
PVH Dom0, so there's likely some work to get it running.

The first step would be to figure out why your host freezes. Are you
running a version of the hypervisor built with debug=y? (that's the
default on staging).

Do you have a serial console setup in order to catch any Xen messages?
In which case, do you get anything on the serial before the reboot?

> Steps to reproduce:
> 1. Start xencommons: sudo ./xen/etc/init.d/xencommons start
> 2. Assign PCI for NIC: sudo ./xen/sbin/xl pci-assignable-add 00:1f.6
> 3. Create HVM DomU: sudo ./xen/sbin/xl create domU_hvm.cfg
> The grub command for xen Dom0 as found in /etc/default/grub:
> GRUB_CMDLINE_XEN="dom0=pvh dom0_mem=8192M,max:8192M loglvl=all
> sync_console_to_ring=true com1=115200,8n1 console=com1

I see you have a serial configured, is there anything printed there
before the reboot?

I would recommend that you also add sync_console in order to make sure
no messages are dropped.

> iommu=debug,verbose,workaround_bios_bug iommu_inclusive

iommu_inclusive is not a valid option [0], you can just drop it.

> xen-pciback.passthrough=1"
> The same problem is present if the above command does not contain
> ‘xen-pciback.passthrough=1’.

You can drop this chunk, that's not a Xen command line option [0].

Thanks, Roger.

[0] https://xenbits.xen.org/docs/unstable/misc/xen-command-line.html

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