Re: [PATCH v14 00/11] KVM: x86/pmu: Guest Last Branch Recording Enabling

Like Xu
2022-09-19T07:26:57Z

On 14/9/2022 7:42 am, Jim Mattson wrote:
> How does live migration work? I don't see any mechanism for recording
> the current LBR MSRs on suspend or restoring them on resume.

Considering that LBR is still a model specific feature, migration is less
valuable unless
both LBR_FMT values of the migration side are the same, the compatibility check
(based on cpu models) is required (gathering dust in my to-do list);

and there is another dusty missing piece is how to ensure that vcpu can get LBR
hardware in
vmx transition when KVM lbr event fails in host lbr event competition, the
complexity here is
that the host and guest may have different LBR filtering options.

The good news is the Architecture LBR will add save/restore support since Paolo
is not averse to
putting more msr's into msrs_to_save_all[], perhaps a dynamic addition mechanism
is a prerequisite.

Please let me know what your priority preferences are for these tasks above.