On Thu, Oct 26, 2023 at 07:14:18PM +0300, Nikolay Borisov wrote: > > if (static_branch_unlikely(&vmx_l1d_should_flush)) > > vmx_l1d_flush(vcpu); > > - else if (cpu_feature_enabled(X86_FEATURE_CLEAR_CPU_BUF)) > > - mds_clear_cpu_buffers(); > > else if (static_branch_unlikely(&mmio_stale_data_clear) && > > kvm_arch_has_assigned_device(vcpu->kvm)) > > + /* MMIO mitigation is mutually exclusive with MDS mitigation later in asm */ > > Mutually exclusive implies that you have one or the other but not both, > whilst I think the right formulation here is redundant? Because if mmio is > enabled mds_clear_cpu_buffers() will clear the buffers here and later > they'll be cleared again, no ? No, because when mmio_stale_data_clear is enabled, X86_FEATURE_CLEAR_CPU_BUF will not be set because of how mitigation is selected in mmio_select_mitigation(): mmio_select_mitigation() { ... /* * Enable CPU buffer clear mitigation for host and VMM if also affected * by MDS or TAA. Otherwise, enable mitigation for VMM only. */ if (boot_cpu_has_bug(X86_BUG_MDS) || (boot_cpu_has_bug(X86_BUG_TAA) && boot_cpu_has(X86_FEATURE_RTM))) setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF); else static_branch_enable(&mmio_stale_data_clear); > Alternatively you might augment this check to only execute iff > X86_FEATURE_CLEAR_CPU_BUF is not set? It already is like that due to the logic above. That is what the comment: /* MMIO mitigation is mutually exclusive with MDS mitigation later in asm */ ... is trying to convey. Suggestions welcome to improve the comment.