linux-kernel - [PATCH] KVM: do not prepare new memslot for KVM_MR

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Date:   Thu, 10 Nov 2022 09:22:04 +0800
From:   Yan Zhao <yan.y.zhao@...el.com>
To:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     pbonzini@...hat.com, seanjc@...gle.com,
        Yan Zhao <yan.y.zhao@...el.com>
Subject: [PATCH] KVM: do not prepare new memslot for KVM_MR_DELETE

kvm_prepare_memory_region() is not useful for KVM_MR_DELETE,
and each kvm_arch_prepare_memory_region() does nothing more than returning
0 for KVM_MR_DELETE.
So, just don't call into kvm_prepare_memory_region() to avoid unnecessary
error handling for KVM_MR_DELETE.

Signed-off-by: Yan Zhao <yan.y.zhao@...el.com>
---
 virt/kvm/kvm_main.c | 52 ++++++++++++++++++++++-----------------------
 1 file changed, 26 insertions(+), 26 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 25d7872b29c1..44e7fb1c376b 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1612,19 +1612,17 @@ static int kvm_prepare_memory_region(struct kvm *kvm,
 	 * new and KVM isn't using a ring buffer, allocate and initialize a
 	 * new bitmap.
 	 */
-	if (change != KVM_MR_DELETE) {
-		if (!(new->flags & KVM_MEM_LOG_DIRTY_PAGES))
-			new->dirty_bitmap = NULL;
-		else if (old && old->dirty_bitmap)
-			new->dirty_bitmap = old->dirty_bitmap;
-		else if (!kvm->dirty_ring_size) {
-			r = kvm_alloc_dirty_bitmap(new);
-			if (r)
-				return r;
+	if (!(new->flags & KVM_MEM_LOG_DIRTY_PAGES))
+		new->dirty_bitmap = NULL;
+	else if (old && old->dirty_bitmap)
+		new->dirty_bitmap = old->dirty_bitmap;
+	else if (!kvm->dirty_ring_size) {
+		r = kvm_alloc_dirty_bitmap(new);
+		if (r)
+			return r;
 
-			if (kvm_dirty_log_manual_protect_and_init_set(kvm))
-				bitmap_set(new->dirty_bitmap, 0, new->npages);
-		}
+		if (kvm_dirty_log_manual_protect_and_init_set(kvm))
+			bitmap_set(new->dirty_bitmap, 0, new->npages);
 	}
 
 	r = kvm_arch_prepare_memory_region(kvm, old, new, change);
@@ -1849,21 +1847,23 @@ static int kvm_set_memslot(struct kvm *kvm,
 		kvm_invalidate_memslot(kvm, old, invalid_slot);
 	}
 
-	r = kvm_prepare_memory_region(kvm, old, new, change);
-	if (r) {
-		/*
-		 * For DELETE/MOVE, revert the above INVALID change.  No
-		 * modifications required since the original slot was preserved
-		 * in the inactive slots.  Changing the active memslots also
-		 * release slots_arch_lock.
-		 */
-		if (change == KVM_MR_DELETE || change == KVM_MR_MOVE) {
-			kvm_activate_memslot(kvm, invalid_slot, old);
-			kfree(invalid_slot);
-		} else {
-			mutex_unlock(&kvm->slots_arch_lock);
+	if (change != KVM_MR_DELETE) {
+		r = kvm_prepare_memory_region(kvm, old, new, change);
+		if (r) {
+			/*
+			 * For MOVE, revert the above INVALID change. No
+			 * modifications required since the original slot was preserved
+			 * in the inactive slots.  Changing the active memslots also
+			 * release slots_arch_lock.
+			 */
+			if (change == KVM_MR_MOVE) {
+				kvm_activate_memslot(kvm, invalid_slot, old);
+				kfree(invalid_slot);
+			} else {
+				mutex_unlock(&kvm->slots_arch_lock);
+			}
+			return r;
 		}
-		return r;
 	}
 
 	/*
-- 
2.17.1