On Tue, May 21, 2024 at 06:40:08PM -0700, Sean Christopherson wrote:
> Add a kvm_vcpu.scheduled_out flag to track if a vCPU is in the process of
> being scheduled out (vCPU put path), or if the vCPU is being reloaded
> after being scheduled out (vCPU load path). In the short term, this will
> allow dropping kvm_arch_sched_in(), as arch code can query scheduled_out
> during kvm_arch_vcpu_load().
>
> Longer term, scheduled_out opens up other potential optimizations, without
> creating subtle/brittle dependencies. E.g. it allows KVM to keep guest
> state (that is managed via kvm_arch_vcpu_{load,put}()) loaded across
> kvm_sched_{out,in}(), if KVM knows the state isn't accessed by the host
> kernel. Forcing arch code to coordinate between kvm_arch_sched_{in,out}()
> and kvm_arch_vcpu_{load,put}() is awkward, not reusable, and relies on the
> exact ordering of calls into arch code.
>
> Adding scheduled_out also obviates the need for a kvm_arch_sched_out()
> hook, e.g. if arch code needs to do something novel when putting vCPU
> state.
>
> And even if KVM never uses scheduled_out for anything beyond dropping
> kvm_arch_sched_in(), just being able to remove all of the arch stubs makes
> it worth adding the flag.
>
> Link: https://lore.kernel.org/all/20240430224431.490139-1-seanjc@xxxxxxxxxx
> Cc: Oliver Upton <oliver.upton@xxxxxxxxx>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Reviewed-by: Oliver Upton <oliver.upton@xxxxxxxxx>
--
Thanks,
Oliver
