KVM: x86/mmu: Allow yielding during MMU notifier unmap/zap, if possible

Let the TDP MMU yield when unmapping a range in response to a MMU
notification, if yielding is allowed by said notification.  There is no
reason to disallow yielding in this case, and in theory the range being
invalidated could be quite large.

Cc: Ben Gardon <bgardon@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210402005658.3024832-11-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu/tdp_mmu.c

@@ -880,7 +880,7 @@ bool kvm_tdp_mmu_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range,
 
 	for_each_tdp_mmu_root(kvm, root, range->slot->as_id)
 		flush |= zap_gfn_range(kvm, root, range->start, range->end,
-				       false, flush);
+				       range->may_block, flush);
 
 	return flush;
 }
@@ -898,6 +898,10 @@ static __always_inline bool kvm_tdp_mmu_handle_gfn(struct kvm *kvm,
 
 	rcu_read_lock();
 
+	/*
+	 * Don't support rescheduling, none of the MMU notifiers that funnel
+	 * into this helper allow blocking; it'd be dead, wasteful code.
+	 */
 	for_each_tdp_mmu_root(kvm, root, range->slot->as_id) {
 		tdp_root_for_each_leaf_pte(iter, root, range->start, range->end)
 			ret |= handler(kvm, &iter, range);