Re: [Xen-users] issues with pvh mode for dom0 and domU on xen 4.5.0 / kernel 3.18.9

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

Hello,

El 15/06/15 a les 0.46, Atom2 ha escrit:
> Hi guys,
> I recently switched from xen 4.4.2 to 4.5.0 after it became stable on
> gentoo (kernel version is 3.18.9) and thought I'd give pvh for both dom0
> and domUs a spin - unfortunately with not too much success:
> 
> 
> DOM0:
> For dom0 I simply added dom0pvh=1 to the xen command line. The system
> booted up and I was also able to confirm that dom0 is running in the
> correct mode by checking with xen-detect.
> 
> What I however found out is that xen creates a bunch of error/warning
> messages some of which make it to xl's dmesg file (the majority seems to
> get dropped due to rate limits). None of these messages are there when
> started without dom0pvh=1. Please see the two attached files for a
> comparision between the xl dmesg for PVH ("dmesg.xl.pvh") and the xl
> dmesg in non-PVH mode ("dmesg.xl").
> 
> There are a few (most likely irrelevant) differences at line 109 to 111
> relating to messages about the "Start info", the "Page tables", and the
> "Boot stack". The main difference is in the additional lines in the file
> "dmesg.xl.pvh" on line numbers 121-122 and 124-156 including 8 lines
> about suppressed messages totalling in excess of 236.000 (ignored)
> messages.  It's probably worth noteing that no further messages make it
> to xl's dmesg and also /var/log/messages does not have anything strange
> once the dom0 is up and running.

Those are errors from the IOMMU, your BIOS is probably missing some RMRR
regions. Do you know which devices are at 0000:00:1a.0 and 0000:00:02.0?

(XEN) [VT-D]DMAR:[DMA Read] Request device [0000:00:1a.0] fault addr
dc086000, iommu reg = ffff82c000203000
(XEN) [VT-D]DMAR: reason 06 - PTE Read access is not set

The above error looks reasonable, this memory is between 3 and 4 GiB
which matches the MMIO hole.

(XEN) [VT-D]DMAR:[DMA Write] Request device [0000:00:02.0] fault addr
72c481000, iommu reg = ffff82c000201000
(XEN) [VT-D]DMAR: reason 05 - PTE Write access is not set

This however is very high address, and is within a region marked as
usable in the memory map:

(XEN)  0000000100000000 - 000000081e600000 (usable)

There are some patches on the list to add additional RMRR regions on the
command line, however they are not committed yet, so there's not much
you can try right now (apart from trying it on a different box).

> It, however, appears that the pvh dom0 compared to the standard dom0
> consumes _significantly_ more CPU time as shown by "xl info" from within
> dom0 - which to me seems counter-intuitive given my (limited)
> understanding of what pvh tries to achieve.
> 
> 
> DOMU:
> For a test domU I just added pvh=1 to it's (otherwise unchanged)
> configuration file and tried to start the domU by issuing
> xl -v -v -v /path/to/config/file -c
> 
> The domU did not come up at all (but works flawlessly when commenting
> out the pvh=1 configuration line); details of the xl command output for
> the failed attempt can be found in the attached file xl.domU. I honestly
> can't make much sense out of the error message which in essence seems to
> complain about an unsupported feature and a missing file or directory
> before giving up.

AFAICT from the log provided you seem to be trying to launch a MiniOS
based guest with pvh=1, which is not supported. MiniOS doesn't support
the PVH mode yet.

Roger.

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