On Mon, Oct 31, 2022, Gavin Shan wrote: > The VCPU isn't expected to be runnable when the dirty ring becomes soft > full, until the dirty pages are harvested and the dirty ring is reset > from userspace. So there is a check in each guest's entrace to see if > the dirty ring is soft full or not. The VCPU is stopped from running if > its dirty ring has been soft full. The similar check will be needed when > the feature is going to be supported on ARM64. As Marc Zyngier suggested, > a new event will avoid pointless overhead to check the size of the dirty > ring ('vcpu->kvm->dirty_ring_size') in each guest's entrance. > > Add KVM_REQ_DIRTY_RING_SOFT_FULL. The event is raised when the dirty ring > becomes soft full in kvm_dirty_ring_push(). The event is cleared in the > check, done in the newly added helper kvm_dirty_ring_check_request(), or > when the dirty ring is reset by userspace. Since the VCPU is not runnable > when the dirty ring becomes soft full, the KVM_REQ_DIRTY_RING_SOFT_FULL > event is always set to prevent the VCPU from running until the dirty pages > are harvested and the dirty ring is reset by userspace. > > kvm_dirty_ring_soft_full() becomes a private function with the newly added > helper kvm_dirty_ring_check_request(). The alignment for the various event > definitions in kvm_host.h is changed to tab character by the way. In order > to avoid using 'container_of()', the argument @ring is replaced by @vcpu > in kvm_dirty_ring_push() and kvm_dirty_ring_reset(). The argument @kvm to > kvm_dirty_ring_reset() is dropped since it can be retrieved from the VCPU. > > Link: https://lore.kernel.org/kvmarm/87lerkwtm5.wl-maz@xxxxxxxxxx > Suggested-by: Marc Zyngier <maz@xxxxxxxxxx> > Signed-off-by: Gavin Shan <gshan@xxxxxxxxxx> > Reviewed-by: Peter Xu <peterx@xxxxxxxxxx> > --- Reviewed-by: Sean Christopherson <seanjc@xxxxxxxxxx> > @@ -142,13 +144,17 @@ int kvm_dirty_ring_reset(struct kvm *kvm, struct kvm_dirty_ring *ring) > > kvm_reset_dirty_gfn(kvm, cur_slot, cur_offset, mask); > > + if (!kvm_dirty_ring_soft_full(ring)) > + kvm_clear_request(KVM_REQ_DIRTY_RING_SOFT_FULL, vcpu); > + Marc, Peter, and/or Paolo, can you confirm that clearing the request here won't cause ordering problems? Logically, this makes perfect sense (to me, since I suggested it), but I'm mildly concerned I'm overlooking an edge case where KVM could end up with a soft-full ring but no pending request. > trace_kvm_dirty_ring_reset(ring); > > return count; > } >