KVM: Reinstall old memslots if arch preparation fails

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@arm.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 70f03ce0e5c1d547beaa2d206ce6687f292a3b48..6e99525d7dcec9330a7f20b42afc9115a4d72337 100644 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -999,7 +999,7 @@ 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;
 
@@ -1107,7 +1107,13 @@ 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.
@@ -1117,13 +1123,6 @@ int __kvm_set_memory_region(struct kvm *kvm,
                 *      - kvm_is_visible_gfn (mmu_check_root)
                 */
                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);
@@ -1137,15 +1136,17 @@ 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);