Re: [Libguestfs] [PATCH v2v] convert: linux: Require host cpu for all RHEL-alike >= 9

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/a3e45b3ea5b45e682cb4b7ad3a5...

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(a)redhat.com >> https://listman.redhat.com/mailman/listinfo/libguestfs >> > > With regards, > Daniel > -- > |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| > |: https://libvirt.org -o- https://fstop138.berrange.com :| > |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|