Re: [RFC PATCH 2/2] kvm/kvm-all.c: listener should delay kvm_vm_ioctl to the commit phase

[Emanuele Giuseppe Esposito]

>> One thing I forgot to ask: iirc we used to have a workaround to kick all
>> vcpus out, update memory slots, then continue all vcpus.  Would that work
>> for us too for the problem you're working on?
> 
> As reference, here is one such approach for region resizes only:
> 
> https://lore.kernel.org/qemu-devel/20200312161217.3590-1-david@redhat.com/
> 
> which notes:
> 
> "Instead of inhibiting during the region_resize(), we could inhibit for
> the hole memory transaction (from begin() to commit()). This could be
> nice, because also splitting of memory regions would be atomic (I
> remember there was a BUG report regarding that), however, I am not sure
> if that might impact any RT users."
> 
> 
I read:

"Using pause_all_vcpus()/resume_all_vcpus() is not possible, as it will
temporarily drop the BQL - something most callers can't handle (esp.
when called from vcpu context e.g., in virtio code)."

Thank you,
Emanuele