libvirt users - Nov 2020 - Re: image works in native but not in vm when cpu mode='host-passthrough' is set

Greetings.

I have an image I've created with a bunch of chost flags which works on my
machine when it comes to native boot.
if I take that same image into a vm managed via libvirt, I get kernel panic.
I'd assume that something is missing from my vm config, question is what and
what I can do about it?
here is the flags part of lscpu in native and vm: https://dpaste.com/3TR8QJ5G8
and the vm's xml: https://dpaste.com/984JX4LUQ
if I build the image with the default flags (march=x86-64), the vm boots well.
my new chost is -O2 -pipe -march=skylake -mabm -mno-adx -mno-avx -mno-avx2
-mno-bmi -mno-bmi2 -mno-f16c -mno-fma -mno-xsave -mno-xsavec -mno-xsaveopt
-mno-xsaves -mno-sgx
the cpu is Intel(R) Pentium(R) CPU G4560 @ 3.50GHz

thoughts?

Thanks,

Dagg.

On Tue, Nov 17, 2020 at 11:32:29AM +0100, daggs wrote:
>Greetings.
>
>I have an image I've created with a bunch of chost flags which works on
my machine when it comes to native boot.
>if I take that same image into a vm managed via libvirt, I get kernel panic.
>I'd assume that something is missing from my vm config, question is what
and what I can do about it?
>here is the flags part of lscpu in native and vm:
https://dpaste.com/3TR8QJ5G8
>and the vm's xml: https://dpaste.com/984JX4LUQ
>if I build the image with the default flags (march=x86-64), the vm boots
well.
>my new chost is -O2 -pipe -march=skylake -mabm -mno-adx -mno-avx -mno-avx2
-mno-bmi -mno-bmi2 -mno-f16c -mno-fma -mno-xsave -mno-xsavec -mno-xsaveopt
-mno-xsaves -mno-sgx
>the cpu is Intel(R) Pentium(R) CPU G4560 @ 3.50GHz
>
Not sure, but there might be some flags that are not passed through even with
host-passthrough.  Virtualisation ones are definitely one of those that need to
be enabled on top of host-passthrough.  The easiest thing to check that I can
think of would be booting some live distro and checking the flags in
/proc/cpuinfo and how are they different from your host.
>thoughts?
>
>Thanks,
>
>Dagg.
>

Greetings Martin,
> Sent: Thursday, November 19, 2020 at 11:23 PM
> From: "Martin Kletzander" <mkletzan@redhat.com>
> To: "daggs" <daggs@gmx.com>
> Cc: "libvirt-usersredhat.com" <libvirt-users@redhat.com>
> Subject: Re: image works in native but not in vm when cpu
mode='host-passthrough' is set
>
> On Tue, Nov 17, 2020 at 11:32:29AM +0100, daggs wrote:
> ...
> Not sure, but there might be some flags that are not passed through even
with
> host-passthrough.  Virtualisation ones are definitely one of those that
need to
> be enabled on top of host-passthrough.  The easiest thing to check that I
can
> think of would be booting some live distro and checking the flags in
> /proc/cpuinfo and how are they different from your host.
>
I don't need livecd, I can diff both native and vm, see
https://dpaste.com/ARETBEPCL
from what I can see, the vm is missing these flags: dts acpi tm pbe art pebs bts
nonstop_tsc aperfmperf dtes64 monitor ds_cpl est tm2 sdbg xtpr pdcm epb intel_pt
dtherm pln pts hwp hwp_notify hwp_act_window hwp_epp
and have these flags: tsc_known_freq hypervisor umip arch_capabilities

beside the acpi flag which I found strange to be messing, I can't think of
any other flag which might be needed.

Dagg.