On Fri, Dec 17, 2021 at 04:54:22PM +0100, Paolo Bonzini wrote: > On 12/17/21 15:38, Mark Rutland wrote: > > For example kvm_guest_enter_irqoff() calls guest_enter_irq_off() which calls > > vtime_account_guest_enter(), but kvm_guest_exit_irqoff() doesn't call > > guest_exit_irq_off() and the call to vtime_account_guest_exit() is open-coded > > elsewhere. Also, guest_enter_irq_off() conditionally calls > > rcu_virt_note_context_switch(), but I can't immediately spot anything on the > > exit side that corresponded with that, which looks suspicious. > > rcu_note_context_switch() is a point-in-time notification; it's not strictly > necessary, but it may improve performance a bit by avoiding unnecessary IPIs > from the RCU subsystem. > > There's no benefit from doing it when you're back from the guest, because at > that point the CPU is just running normal kernel code. Do scheduling-clock interrupts from guest mode have the "user" parameter set? If so, that would keep RCU happy. Thanx, Paul
