Control: severity -1 normal
On Wed, 18 Jun 2025 10:24:11 +0200 Philipp Kern <[email protected]> wrote:
On 6/18/25 10:14 AM, Michael Tokarev wrote:
> On 18.06.2025 11:02, Philipp Kern wrote:
> []
>> It'd be great if qemu could autodetect this, i.e. presumably use
>> getconf(PAGE_SIZE) for this.
>
> As has been explained to me by the qemu ppc people, autodetecting this
> is wrong because this way qemu will start with different configuration
> on different hosts, and the virtual machines will be unpredictable
> non-migratable. I don't know how important this is, though - probably
> being able to start in the first place is more important.
Aren't they non-migratable anyway if the host kernel page size config
differs? I.e. if you are already diverging there between multiple hosts,
you lost the ability to migrate because it would not be runnable either
- not just unable to start. But I surely miss something here. :)
The point is that by default, qemu creates machines with deterministic
configuration. If this configuration is not supported on a given HW, it
fails to start. You have to explicitly specify a non-default config
(on all machines when you want the VM to be migratable).
It is similar to using -cpu host automatically together with -enable-kvm
-- it is a fine default as long as you don't consider migration. So
instead, qemu uses some minimal common cpu type, and you have to
explicitly specify the cpu (on all nodes) when you know all your nodes
handles it.
Either way, I don't see why this bug has "serious" severity. To me, it
is a wishlist severity, but let's keep it as "normal".
And either way, I don't want to divirge from the upstream here. So it
is probably "wontfix" too.
Thanks,
/mjt
