On Mon, Feb 06, 2023 at 12:37:30PM +0000, Daniel P. Berrangé wrote:
> On Mon, Feb 06, 2023 at 12:19:40PM +0000, Richard W.M. Jones wrote:
> > RHEL >= 9 and compatible distros like Rocky >= 9 will not boot using
> > the default qemu CPU. You will see an error at boot:
> >
> > Fatal glibc error: CPU does not support x86-64-v2
> >
> > Instead you need to use -cpu host.
> >
> > In commit f28757c6d1 ("convert_linux: set "gcaps_default_cpu = false"
> > for x86_64 RHEL-9.0+ guests") we fixed this specifically for RHEL >= 9.
> >
> > This commit extends the same fix to all RHEL family distros.
>
> If v2v is going to use host CPU for a bunch of distros, why not use
> it for all distros ? What's the downside in -cpu host, instead of
> the default qemu64 CPU ?
>
> Even if the distro doesn't require x86_64-v2 ABI, they'll pretty much
> all benefit from NOT using the default QEMU CPU model, if only for
> the fact that they gain the 'aesni' feature which increases crypto
> performance massively.
I don't know what we should do, but the current code does this:
(1) If a particular CPU model is specified by the source hypervisor
(eg VMware), use that.
(2) If the guest is RHEL family >= 9, use -cpu host / host-passthrough
(3) Otherwise don't specify any -cpu or <cpu> section
The third option seems to cause qemu / libvirt to use qemu64. However
it has the advantage that the guest is migratable afterwards.
There may be a case for changing this so:
(a) Rule (2) is changed so we use host-model (for the libvirt target).
(b) Rule (3) is changed so we always specify a minimum CPU, eg.
for x86-64 guests, choose x86-64-v2 (is that an actual CPU model??)
(a) seems like a no-brainer. Not sure why we chose host-passthrough
instead of host-model? The explanation in the commit message is not
very convincing:
https://github.com/libguestfs/virt-v2v/commit/a3e45b3ea5b45e682cb4b7ad3a5646586c6c7886
I think (b) is fraught because it is my understanding that there is no
good choice for a minimum CPU since we don't know anything about the
target hardware (eg. if it's Intel or AMD). And on !x86-64 we really
have no idea at all what's a good choice.
Other management systems like RHV, KubeVirt are probably ignoring our
CPU metadata anyway ...
Rich.
> >
> > Updates: commit f28757c6d100060c65212ea55cfa59d308dcb850
> > Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=2166619
> > Reported-by: Ming Xie
> > Thanks: Laszlo Ersek
> > ---
> > convert/convert_linux.ml | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/convert/convert_linux.ml b/convert/convert_linux.ml
> > index e20cafa551..460cbff0ed 100644
> > --- a/convert/convert_linux.ml
> > +++ b/convert/convert_linux.ml
> > @@ -201,9 +201,9 @@ let convert (g : G.guestfs) source inspect i_firmware
> > keep_serial_console _ =
> >
> > (* RHEL >= 9.0 on x86_64 requires the processor to support the
> > "x86-64-v2"
> > * microarchitecture level, which the default QEMU VCPU model does not
> > - * satisfy. Refer to RHBZ#2076013.
> > + * satisfy. Refer to RHBZ#2076013 RHBZ#2166619.
> > *)
> > - let default_cpu_suffices = inspect.i_distro <> "rhel" ||
> > + let default_cpu_suffices = family <> `RHEL_family ||
> > inspect.i_arch <> "x86_64" ||
> > inspect.i_major_version < 9 in
> >
> > --
> > 2.39.0
> >
> > _______________________________________________
> > Libguestfs mailing list
> > Libguestfs@redhat.com
> > https://listman.redhat.com/mailman/listinfo/libguestfs
> >
>
> With regards,
> Daniel
> --
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--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
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