KVM: x86/mmu: Factor out spte atomic bit clearing routine

This new function, tdp_mmu_clear_spte_bits_atomic(), will be used in a
follow-up patch to enable lockless Accessed bit clearing.

Signed-off-by: James Houghton <jthoughton@google.com>
Acked-by: Yu Zhao <yuzhao@google.com>
Link: https://lore.kernel.org/r/20250204004038.1680123-4-jthoughton@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: 48ca

arch/x86/kvm/mmu/tdp_iter.h

@@ -25,6 +25,13 @@ static inline u64 kvm_tdp_mmu_write_spte_atomic(tdp_ptep_t sptep, u64 new_spte)
 	return xchg(rcu_dereference(sptep), new_spte);
 }
 
+static inline u64 tdp_mmu_clear_spte_bits_atomic(tdp_ptep_t sptep, u64 mask)
+{
+	atomic64_t *sptep_atomic = (atomic64_t *)rcu_dereference(sptep);
+
+	return (u64)atomic64_fetch_and(~mask, sptep_atomic);
+}
+
 static inline void __kvm_tdp_mmu_write_spte(tdp_ptep_t sptep, u64 new_spte)
 {
 	KVM_MMU_WARN_ON(is_ept_ve_possible(new_spte));
@@ -63,12 +70,8 @@ static inline u64 kvm_tdp_mmu_write_spte(tdp_ptep_t sptep, u64 old_spte,
 static inline u64 tdp_mmu_clear_spte_bits(tdp_ptep_t sptep, u64 old_spte,
 					  u64 mask, int level)
 {
-	atomic64_t *sptep_atomic;
-
-	if (kvm_tdp_mmu_spte_need_atomic_write(old_spte, level)) {
-		sptep_atomic = (atomic64_t *)rcu_dereference(sptep);
-		return (u64)atomic64_fetch_and(~mask, sptep_atomic);
-	}
+	if (kvm_tdp_mmu_spte_need_atomic_write(old_spte, level))
+		return tdp_mmu_clear_spte_bits_atomic(sptep, mask);
 
 	__kvm_tdp_mmu_write_spte(sptep, old_spte & ~mask);
 	return old_spte;