On Wed, Jan 17, 2024 at 12:50 AM Christian Borntraeger <borntraeger@xxxxxxxxxxxxx> wrote: > > > > Am 15.01.24 um 17:01 schrieb Yi Wang: > > Many thanks for your such kind and detailed reply, Sean! > > .... > >> > >> So instead of special casing x86, what if we instead have KVM setup an empty > >> IRQ routing table during kvm_create_vm(), and then avoid this mess entirely? > >> That way x86 and s390 no longer need to set empty/dummy routing when creating > >> an IRQCHIP, and the worst case scenario of userspace misusing an ioctl() is no > >> longer a NULL pointer deref. > > Sounds like a good idea. This should also speedup guest creation on s390 since > it would avoid one syncronize_irq. > > > > To setup an empty IRQ routing table during kvm_create_vm() sounds a good idea, > > at this time vCPU have not been created and kvm->lock is held so skipping > > synchronization is safe here. > > > > However, there is one drawback, if vmm wants to emulate irqchip > > itself, e.g. qemu > > with command line '-machine kernel-irqchip=off' may not need irqchip > > in kernel. How > > do we handle this issue? > > I would be fine with wasted memory. The only question is does it have a functional > impact or can we simply ignore the dummy routing. > Thanks for your reply, I will update the patch. -- --- Best wishes Yi Wang
