> > The special handling for LA57 is from the patch "kvm: x86: Return LA57 > feature based on hardware capability". > https://lore.kernel.org/lkml/1548950983-18458-1-git-send-email-yu.c.zhang@xxxxxxxxxxxxxxx/ > > The reason is host kernel may disable 5-level paging using cmdline parameter > 'no5lvl', and it will clear the feature bit for LA57 in boot_cpu_data. > boot_cpu_data is queried in kvm_set_cpu_caps to derive kvm cpu cap masks. > > " VMs can still benefit from extended linear address width, e.g. to enhance > features like ASLR" even when host doesn't use 5-level paging. > So, the patch sets LA57 based on hardware capability. > > I was just wondering whether LAM could be the similar case that the host > disabled the feature somehow (e.g via clearcpuid), and the guest still want > to use it. Paging modes in root & non-root are orthogonal, so should LAM. B.R. Yu
