KVM: selftests: Test IPI to halted vCPU in xAPIC while backing page moves

When a guest is using xAPIC KVM allocates a backing page for the required
EPT entry for the APIC access address set in the VMCS. If mm decides to
move that page the KVM mmu notifier will update the VMCS with the new
HPA. This test induces a page move to test that APIC access continues to
work correctly. It is a directed test for
commit e649b3f0

 "KVM: x86: Fix APIC page invalidation race".

Tested: ran for 1 hour on a skylake, migrating backing page every 1ms

Depends on patch "selftests: kvm: Add exception handling to selftests"
from aaronlewis@google.com that has not yet been queued.

Signed-off-by: Peter Shier <pshier@google.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Reviewed-by: Ricardo Koller <ricarkol@google.com>
Message-Id: <20201105223823.850068-1-pshier@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>