A flaw was discovered in the way that the KVM hypervisor handled
instruction emulation for an L2 guest when nested virtualisation is
enabled. Under some circumstances, an L2 guest may trick the L0 guest into
accessing sensitive L1 resources that should be inaccessible to the L2
guest.

Paulo Bonzini discovered that the KVM hypervisor implementation in the
Linux kernel could improperly let a nested (level 2) guest access the
resources of a parent (level 1) guest in certain situations. An attacker
could use this to expose sensitive information.

sbeattie

only systems running Intel processors are affected.