KVM: x86: do not pass poisoned hva to __kvm_set_memory_region

__kvm_set_memory_region does not use the hva at all, so trying to
catch use-after-delete is pointless and, worse, it fails access_ok
now that we apply it to all memslots including private kernel ones.
This fixes an AVIC regression.

Fixes: 09d952c ("KVM: check userspace_addr for all memslots")
Reported-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/x86.c

@@ -9951,13 +9951,8 @@ int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size)
 		if (!slot || !slot->npages)
 			return 0;
 
-		/*
-		 * Stuff a non-canonical value to catch use-after-delete.  This
-		 * ends up being 0 on 32-bit KVM, but there's no better
-		 * alternative.
-		 */
-		hva = (unsigned long)(0xdeadull << 48);
 		old_npages = slot->npages;
+		hva = 0;
 	}
 
 	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {