KVM: x86/mmu: Change tdp_mmu_{set,zap}_spte_atomic() to return 0/-EBUSY

tdp_mmu_set_spte_atomic() and tdp_mmu_zap_spte_atomic() return a bool
with true indicating the SPTE modification was successful and false
indicating failure. Change these functions to return an int instead
since that is the common practice.

Opportunistically fix up the kernel-doc style for the Return section
above tdp_mmu_set_spte_atomic().

No functional change intended.
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: David Matlack <dmatlack@google.com>
Message-Id: <20220119230739.2234394-5-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu/tdp_mmu.c

@@ -518,11 +518,13 @@ static void handle_changed_spte(struct kvm *kvm, int as_id, gfn_t gfn,
  * @kvm: kvm instance
  * @iter: a tdp_iter instance currently on the SPTE that should be set
  * @new_spte: The value the SPTE should be set to
- * Returns: true if the SPTE was set, false if it was not. If false is returned,
- *          this function will have no side-effects other than setting
- *          iter->old_spte to the last known value of spte.
+ * Return:
+ * * 0      - If the SPTE was set.
+ * * -EBUSY - If the SPTE cannot be set. In this case this function will have
+ *            no side-effects other than setting iter->old_spte to the last
+ *            known value of the spte.
  */
-static inline bool tdp_mmu_set_spte_atomic(struct kvm *kvm,
+static inline int tdp_mmu_set_spte_atomic(struct kvm *kvm,
 					  struct tdp_iter *iter,
 					  u64 new_spte)
 {
@@ -538,7 +540,7 @@ static inline bool tdp_mmu_set_spte_atomic(struct kvm *kvm,
 	 * may modify it.
 	 */
 	if (is_removed_spte(iter->old_spte))
-		return false;
+		return -EBUSY;
 
 	/*
 	 * Note, fast_pf_fix_direct_spte() can also modify TDP MMU SPTEs and
@@ -553,27 +555,30 @@ static inline bool tdp_mmu_set_spte_atomic(struct kvm *kvm,
 		 * tdp_mmu_set_spte_atomic().
 		 */
 		iter->old_spte = old_spte;
-		return false;
+		return -EBUSY;
 	}
 
 	__handle_changed_spte(kvm, iter->as_id, iter->gfn, iter->old_spte,
 			      new_spte, iter->level, true);
 	handle_changed_spte_acc_track(iter->old_spte, new_spte, iter->level);
 
-	return true;
+	return 0;
 }
 
-static inline bool tdp_mmu_zap_spte_atomic(struct kvm *kvm,
+static inline int tdp_mmu_zap_spte_atomic(struct kvm *kvm,
 					  struct tdp_iter *iter)
 {
+	int ret;
+
 	/*
 	 * Freeze the SPTE by setting it to a special,
 	 * non-present value. This will stop other threads from
 	 * immediately installing a present entry in its place
 	 * before the TLBs are flushed.
 	 */
-	if (!tdp_mmu_set_spte_atomic(kvm, iter, REMOVED_SPTE))
-		return false;
+	ret = tdp_mmu_set_spte_atomic(kvm, iter, REMOVED_SPTE);
+	if (ret)
+		return ret;
 
 	kvm_flush_remote_tlbs_with_address(kvm, iter->gfn,
 					   KVM_PAGES_PER_HPAGE(iter->level));
@@ -588,7 +593,7 @@ static inline bool tdp_mmu_zap_spte_atomic(struct kvm *kvm,
 	 */
 	WRITE_ONCE(*rcu_dereference(iter->sptep), 0);
 
-	return true;
+	return 0;
 }
 
 
@@ -785,7 +790,7 @@ static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
 		if (!shared) {
 			tdp_mmu_set_spte(kvm, &iter, 0);
 			flush = true;
-		} else if (!tdp_mmu_zap_spte_atomic(kvm, &iter)) {
+		} else if (tdp_mmu_zap_spte_atomic(kvm, &iter)) {
 			goto retry;
 		}
 	}
@@ -943,7 +948,7 @@ static int tdp_mmu_map_handle_target_level(struct kvm_vcpu *vcpu,
 
 	if (new_spte == iter->old_spte)
 		ret = RET_PF_SPURIOUS;
-	else if (!tdp_mmu_set_spte_atomic(vcpu->kvm, iter, new_spte))
+	else if (tdp_mmu_set_spte_atomic(vcpu->kvm, iter, new_spte))
 		return RET_PF_RETRY;
 
 	/*
@@ -1009,7 +1014,7 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
 		 */
 		if (is_shadow_present_pte(iter.old_spte) &&
 		    is_large_pte(iter.old_spte)) {
-			if (!tdp_mmu_zap_spte_atomic(vcpu->kvm, &iter))
+			if (tdp_mmu_zap_spte_atomic(vcpu->kvm, &iter))
 				break;
 
 			/*
@@ -1035,7 +1040,7 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
 			new_spte = make_nonleaf_spte(child_pt,
 						     !shadow_accessed_mask);
 
-			if (tdp_mmu_set_spte_atomic(vcpu->kvm, &iter, new_spte)) {
+			if (!tdp_mmu_set_spte_atomic(vcpu->kvm, &iter, new_spte)) {
 				tdp_mmu_link_page(vcpu->kvm, sp,
 						  fault->huge_page_disallowed &&
 						  fault->req_level >= iter.level);
@@ -1218,7 +1223,7 @@ static bool wrprot_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
 
 		new_spte = iter.old_spte & ~PT_WRITABLE_MASK;
 
-		if (!tdp_mmu_set_spte_atomic(kvm, &iter, new_spte))
+		if (tdp_mmu_set_spte_atomic(kvm, &iter, new_spte))
 			goto retry;
 
 		spte_set = true;
@@ -1281,7 +1286,7 @@ static bool clear_dirty_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
 				continue;
 		}
 
-		if (!tdp_mmu_set_spte_atomic(kvm, &iter, new_spte))
+		if (tdp_mmu_set_spte_atomic(kvm, &iter, new_spte))
 			goto retry;
 
 		spte_set = true;
@@ -1407,7 +1412,7 @@ static void zap_collapsible_spte_range(struct kvm *kvm,
 			continue;
 
 		/* Note, a successful atomic zap also does a remote TLB flush. */
-		if (!tdp_mmu_zap_spte_atomic(kvm, &iter))
+		if (tdp_mmu_zap_spte_atomic(kvm, &iter))
 			goto retry;
 	}