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

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
not 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>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
[bwh: Backported to 5.3:
 - Update another error path in kvm_create_vm() to use out_err_no_mmu_notifier
 - Adjust context]

Gbp-Pq: Topic bugfix/x86/itlb_multihit
Gbp-Pq: Name 0006-kvm-x86-mmu-Recovery-of-shattered-NX-large-pages.patch