On 2/21/2023 7:13 PM, Yu Zhang wrote:
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.
Agree.
B.R.
Yu
