[PATCH v4 02/19] KVM: Reinstall old memslots if arch preparation fails

[Sean Christopherson]

Reinstall the old memslots if preparing the new memory region fails
after invalidating a to-be-{re}moved memslot.

Remove the superfluous 'old_memslots' variable so that it's somewhat
clear that the error handling path needs to free the unused memslots,
not simply the 'old' memslots.

Fixes: bc6678a33d9b9 ("KVM: introduce kvm->srcu and convert kvm_set_memory_region to SRCU update")
Reviewed-by: Christoffer Dall <christoffer.dall@xxxxxxx>
Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
---
 virt/kvm/kvm_main.c | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 3aa21bec028d..f14bde936c09 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1002,7 +1002,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
 	unsigned long npages;
 	struct kvm_memory_slot *slot;
 	struct kvm_memory_slot old, new;
-	struct kvm_memslots *slots = NULL, *old_memslots;
+	struct kvm_memslots *slots;
 	int as_id, id;
 	enum kvm_mr_change change;
 
@@ -1110,7 +1110,13 @@ int __kvm_set_memory_region(struct kvm *kvm,
 		slot = id_to_memslot(slots, id);
 		slot->flags |= KVM_MEMSLOT_INVALID;
 
-		old_memslots = install_new_memslots(kvm, as_id, slots);
+		/*
+		 * We can re-use the old memslots, the only difference from the
+		 * newly installed memslots is the invalid flag, which will get
+		 * dropped by update_memslots anyway.  We'll also revert to the
+		 * old memslots if preparing the new memory region fails.
+		 */
+		slots = install_new_memslots(kvm, as_id, slots);
 
 		/* From this point no new shadow pages pointing to a deleted,
 		 * or moved, memslot will be created.
@@ -1120,13 +1126,6 @@ int __kvm_set_memory_region(struct kvm *kvm,
 		 *	- kvm_is_visible_gfn (mmu_check_roots)
 		 */
 		kvm_arch_flush_shadow_memslot(kvm, slot);
-
-		/*
-		 * We can re-use the old_memslots from above, the only difference
-		 * from the currently installed memslots is the invalid flag.  This
-		 * will get overwritten by update_memslots anyway.
-		 */
-		slots = old_memslots;
 	}
 
 	r = kvm_arch_prepare_memory_region(kvm, &new, mem, change);
@@ -1140,15 +1139,17 @@ int __kvm_set_memory_region(struct kvm *kvm,
 	}
 
 	update_memslots(slots, &new, change);
-	old_memslots = install_new_memslots(kvm, as_id, slots);
+	slots = install_new_memslots(kvm, as_id, slots);
 
 	kvm_arch_commit_memory_region(kvm, mem, &old, &new, change);
 
 	kvm_free_memslot(kvm, &old, &new);
-	kvfree(old_memslots);
+	kvfree(slots);
 	return 0;
 
 out_slots:
+	if (change == KVM_MR_DELETE || change == KVM_MR_MOVE)
+		slots = install_new_memslots(kvm, as_id, slots);
 	kvfree(slots);
 out_free:
 	kvm_free_memslot(kvm, &new, &old);
-- 
2.24.1