UBUNTU: SAUCE: kvm: x86: mmu: Recovery of shattered NX large pages

UBUNTU: SAUCE: kvm: x86: mmu: Recovery of shattered NX large pages

The page table pages corresponding to broken down large pages are
zapped in FIFO order, so that the large page can potentially
be recovered, if it is no longer being used for execution.  This removes
the performance penalty for walking deeper EPT page tables.

By default, one large page will last about one hour once the guest
reaches a steady state.

Signed-off-by: Junaid Shahid <junaids@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
CVE-2018-12207

[tyhicks: Backport to 4.15
 - Minor context adjustments due to different members of struct
   kvm_mmu_page and kvm_arch]
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>