On 13/11/19 20:30, Sean Christopherson wrote: > Failing to take slots_lock when toggling nx_huge_pages allows multiple > instances of kvm_mmu_zap_all_fast() to run concurrently, as the other > user, KVM_SET_USER_MEMORY_REGION, does not take the global kvm_lock. > Concurrent fast zap instances causes obsolete shadow pages to be > incorrectly identified as valid due to the single bit generation number > wrapping, which results in stale shadow pages being left in KVM's MMU > and leads to all sorts of undesirable behavior. Indeed the current code fails lockdep miserably, but isn't the whole body of kvm_mmu_zap_all_fast() covered by kvm->mmu_lock? What kind of badness can happen if kvm->slots_lock isn't taken? Paolo
