KVM: x86/mmu: Unnest TDP MMU helpers that allocate SPs for eager splitting

Move the implementation of tdp_mmu_alloc_sp_for_split() to its one and
only caller to reduce unnecessary nesting and make it more clear why the
eager split loop continues after allocating a new SP.

Opportunistically drop the double-underscores from
__tdp_mmu_alloc_sp_for_split() now that its parent is gone.

No functional change intended.
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: David Matlack <dmatlack@google.com>
Link: https://lore.kernel.org/r/20240611220512.2426439-4-dmatlack@google.comSigned-off-by: Sean Christopherson <seanjc@google.com>

arch/x86/kvm/mmu/tdp_mmu.c

@@ -1339,7 +1339,7 @@ bool kvm_tdp_mmu_wrprot_slot(struct kvm *kvm,
 	return spte_set;
 }
 
-static struct kvm_mmu_page *__tdp_mmu_alloc_sp_for_split(void)
+static struct kvm_mmu_page *tdp_mmu_alloc_sp_for_split(void)
 {
 	struct kvm_mmu_page *sp;
 
@@ -1356,34 +1356,6 @@ static struct kvm_mmu_page *__tdp_mmu_alloc_sp_for_split(void)
 	return sp;
 }
 
-static struct kvm_mmu_page *tdp_mmu_alloc_sp_for_split(struct kvm *kvm,
-						       struct tdp_iter *iter,
-						       bool shared)
-{
-	struct kvm_mmu_page *sp;
-
-	kvm_lockdep_assert_mmu_lock_held(kvm, shared);
-
-	rcu_read_unlock();
-
-	if (shared)
-		read_unlock(&kvm->mmu_lock);
-	else
-		write_unlock(&kvm->mmu_lock);
-
-	iter->yielded = true;
-	sp = __tdp_mmu_alloc_sp_for_split();
-
-	if (shared)
-		read_lock(&kvm->mmu_lock);
-	else
-		write_lock(&kvm->mmu_lock);
-
-	rcu_read_lock();
-
-	return sp;
-}
-
 /* Note, the caller is responsible for initializing @sp. */
 static int tdp_mmu_split_huge_page(struct kvm *kvm, struct tdp_iter *iter,
 				   struct kvm_mmu_page *sp, bool shared)
@@ -1454,7 +1426,22 @@ static int tdp_mmu_split_huge_pages_root(struct kvm *kvm,
 			continue;
 
 		if (!sp) {
-			sp = tdp_mmu_alloc_sp_for_split(kvm, &iter, shared);
+			rcu_read_unlock();
+
+			if (shared)
+				read_unlock(&kvm->mmu_lock);
+			else
+				write_unlock(&kvm->mmu_lock);
+
+			sp = tdp_mmu_alloc_sp_for_split();
+
+			if (shared)
+				read_lock(&kvm->mmu_lock);
+			else
+				write_lock(&kvm->mmu_lock);
+
+			rcu_read_lock();
+
 			if (!sp) {
 				ret = -ENOMEM;
 				trace_kvm_mmu_split_huge_page(iter.gfn,
@@ -1463,6 +1450,7 @@ static int tdp_mmu_split_huge_pages_root(struct kvm *kvm,
 				break;
 			}
 
+			iter.yielded = true;
 			continue;
 		}