KVM: selftests: Don't bother deleting memslots in KVM when freeing VMs

When freeing a VM, don't call into KVM to manually remove each memslot,
simply cleanup and free any userspace assets associated with the memory
region.  KVM is ultimately responsible for ensuring kernel resources are
freed when the VM is destroyed, deleting memslots one-by-one is
unnecessarily slow, and unless a test is already leaking the VM fd, the
VM will be destroyed when kvm_vm_release() is called.

Not deleting KVM's memslot also allows cleaning up dead VMs without having
to care whether or not the to-be-freed VM is dead or alive.

Reported-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Tested-by: Eric Auger <eric.auger@redhat.com>
Reported-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/kvmarm/Zy0bcM0m-N18gAZz@google.com/
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

Author: sean-jc

tools/testing/selftests/kvm/lib/kvm_util.c

@@ -720,9 +720,6 @@ static void __vm_mem_region_delete(struct kvm_vm *vm,
 	rb_erase(&region->hva_node, &vm->regions.hva_tree);
 	hash_del(&region->slot_node);
 
-	region->region.memory_size = 0;
-	vm_ioctl(vm, KVM_SET_USER_MEMORY_REGION2, &region->region);
-
 	sparsebit_free(&region->unused_phy_pages);
 	sparsebit_free(&region->protected_phy_pages);
 	ret = munmap(region->mmap_start, region->mmap_size);
@@ -1197,7 +1194,12 @@ void vm_mem_region_move(struct kvm_vm *vm, uint32_t slot, uint64_t new_gpa)
  */
 void vm_mem_region_delete(struct kvm_vm *vm, uint32_t slot)
 {
-	__vm_mem_region_delete(vm, memslot2region(vm, slot));
+	struct userspace_mem_region *region = memslot2region(vm, slot);
+
+	region->region.memory_size = 0;
+	vm_ioctl(vm, KVM_SET_USER_MEMORY_REGION2, &region->region);
+
+	__vm_mem_region_delete(vm, region);
 }
 
 void vm_guest_mem_fallocate(struct kvm_vm *vm, uint64_t base, uint64_t size,