[PATCH] KVM: x86/mmu: Rename slot_handle_leaf to slot_handle_level_4k

[David Matlack <dmatlack@google.com>]

slot_handle_leaf is a misnomer because it only operates on 4K SPTEs
whereas "leaf" is used to describe any valid terminal SPTE (4K or
large page). Rename slot_handle_leaf to slot_handle_level_4k to
avoid confusion.

Making this change makes it more obvious there is a benign discrepency
between the legacy MMU and the TDP MMU when it comes to dirty logging.
The legacy MMU only operates on 4K SPTEs when zapping for collapsing
and when clearing D-bits. The TDP MMU, on the other hand, operates on
SPTEs on all levels. The TDP MMU behavior is technically overkill but
not incorrect. So opportunistically add comments to explain the
difference.

Signed-off-by: David Matlack <dmatlack@google.com>
---
 arch/x86/kvm/mmu/mmu.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 24a9f4c3f5e7..f00644e79ef5 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -5382,8 +5382,8 @@ slot_handle_level(struct kvm *kvm, const struct kvm_memory_slot *memslot,
 }
 
 static __always_inline bool
-slot_handle_leaf(struct kvm *kvm, const struct kvm_memory_slot *memslot,
-		 slot_level_handler fn, bool flush_on_yield)
+slot_handle_level_4k(struct kvm *kvm, const struct kvm_memory_slot *memslot,
+		     slot_level_handler fn, bool flush_on_yield)
 {
 	return slot_handle_level(kvm, memslot, fn, PG_LEVEL_4K,
 				 PG_LEVEL_4K, flush_on_yield);
@@ -5772,7 +5772,12 @@ void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm,
 
 	if (kvm_memslots_have_rmaps(kvm)) {
 		write_lock(&kvm->mmu_lock);
-		flush = slot_handle_leaf(kvm, slot, kvm_mmu_zap_collapsible_spte, true);
+		/*
+		 * Strictly speaking only 4k SPTEs need to be zapped because
+		 * KVM never creates intermediate 2m mappings when performing
+		 * dirty logging.
+		 */
+		flush = slot_handle_level_4k(kvm, slot, kvm_mmu_zap_collapsible_spte, true);
 		if (flush)
 			kvm_arch_flush_remote_tlbs_memslot(kvm, slot);
 		write_unlock(&kvm->mmu_lock);
@@ -5809,8 +5814,11 @@ void kvm_mmu_slot_leaf_clear_dirty(struct kvm *kvm,
 
 	if (kvm_memslots_have_rmaps(kvm)) {
 		write_lock(&kvm->mmu_lock);
-		flush = slot_handle_leaf(kvm, memslot, __rmap_clear_dirty,
-					 false);
+		/*
+		 * Strictly speaking only 4k SPTEs need to be cleared because
+		 * KVM always performs dirty logging at a 4k granularity.
+		 */
+		flush = slot_handle_level_4k(kvm, memslot, __rmap_clear_dirty, false);
 		write_unlock(&kvm->mmu_lock);
 	}
 
-- 
2.33.0.882.g93a45727a2-goog