On Fri, 2024-06-07 at 17:06 -0700, Sean Christopherson wrote: > Register KVM's cpuhp and syscore callback when enabling virtualization > in hardware instead of registering the callbacks during initialization, > and let the CPU up/down framework invoke the inner enable/disable > functions. Registering the callbacks during initialization makes things > more complex than they need to be, as KVM needs to be very careful about > handling races between enabling CPUs being onlined/offlined and hardware > being enabled/disabled. > > Intel TDX support will require KVM to enable virtualization during KVM > initialization, i.e. will add another wrinkle to things, at which point > sorting out the potential races with kvm_usage_count would become even > more complex. > > Note, using the cpuhp framework has a subtle behavioral change: enabling > will be done serially across all CPUs, whereas KVM currently sends an IPI > to all CPUs in parallel. While serializing virtualization enabling could > create undesirable latency, the issue is limited to creation of KVM's > first VM, and even that can be mitigated, e.g. by letting userspace force > virtualization to be enabled when KVM is initialized. > > Cc: Chao Gao <chao.gao@xxxxxxxxx> > Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> > --- > Reviewed-by: Kai Huang <kai.huang@xxxxxxxxx>
