[bug report] KVM: Dynamically allocate "new" memslots from the get-go

[Dan Carpenter <dan.carpenter@xxxxxxxxxx>]

Hello Sean Christopherson,

This is a semi-automatic email about new static checker warnings.

The patch 244893fa2859: "KVM: Dynamically allocate "new" memslots
from the get-go" from Dec 6, 2021, leads to the following Smatch
complaint:

    arch/x86/kvm/../../../virt/kvm/kvm_main.c:1526 kvm_prepare_memory_region()
    warn: variable dereferenced before check 'new' (see line 1509)

arch/x86/kvm/../../../virt/kvm/kvm_main.c
  1508		if (change != KVM_MR_DELETE) {
  1509			if (!(new->flags & KVM_MEM_LOG_DIRTY_PAGES))
  1510				new->dirty_bitmap = NULL;
  1511			else if (old && old->dirty_bitmap)
  1512				new->dirty_bitmap = old->dirty_bitmap;
  1513			else if (!kvm->dirty_ring_size) {
  1514				r = kvm_alloc_dirty_bitmap(new);
  1515				if (r)
  1516					return r;
  1517	
  1518				if (kvm_dirty_log_manual_protect_and_init_set(kvm))
  1519					bitmap_set(new->dirty_bitmap, 0, new->npages);
                                                   ^^^^^
  1520			}
  1521		}
  1522	
  1523		r = kvm_arch_prepare_memory_region(kvm, old, new, change);
                                                             ^^^
Lots of unchecked dereferences

  1524	
  1525		/* Free the bitmap on failure if it was allocated above. */
  1526		if (r && new && new->dirty_bitmap && old && !old->dirty_bitmap)
                         ^^^
New check for NULL.  Can this be NULL?

  1527			kvm_destroy_dirty_bitmap(new);
  1528	

regards,
dan carpenter