Explore the challenges and solutions surrounding cache coherency in confidential virtual machines during this Linux Plumbers Conference talk. Delve into the limitations of AMD's SME_COHERENT feature and its impact on cache coherence between CPUs and devices. Examine the security implications, including CVE-2022-0171, and the performance issues arising from current mitigation strategies. Investigate potential solutions, such as using VMPAGE_FLUSH MSR instead of wbinvd and leveraging mmu_notifiers to conditionally flush caches. Gain insights into the complexities of managing cache coherency in confidential computing environments and the ongoing efforts to balance security and performance in virtualized systems.