Re: [PATCH] KVM: x86: Include host suspended time in steal time.

Suleiman Souhlal
2024-08-15T04:33:18Z

On Thu, Aug 15, 2024 at 12:35 AM Sean Christopherson <seanjc@google.com> wrote:
>
> On Wed, Aug 14, 2024, Suleiman Souhlal wrote:
>
> > With the proposed approach, the steal time page would get copied to the new
> > host and everything would keep working correctly, with the exception of a
> > possible host suspend happening between when the migration started and when
> > it finishes, not being reflected post-migration. That seems like a
> > reasonable compromise.
>
> Maybe, but I'm not keen on sweeping this under the rug. Ignoring issues because
> they'll "never" happen has bitten KVM more than once.
>
> At the absolute bare minimum, the flaw needs to be documented, with a suggested
> workaround provided (do KVM on all vCPUs before migrating after suspend), e.g.
> so that userspace can workaround the issue in the unlikely scenario userspace
> does suspend+resume, saves/restores a VM, *and* cares about steal-time.

I can write a comment in record_steal_time() that describes the
scenario, mention it in
the commit message and add something to the steal time part of
Documentation/virt/kvm/x86/msr.rst.

-- Suleiman