Re: [Qemu-devel] About QEMU BQL and dirty log switch in Migration

[Paolo Bonzini]

On 11/05/2017 14:07, Zhoujian (jay) wrote:
> -        * Scan sptes if dirty logging has been stopped, dropping those
> -        * which can be collapsed into a single large-page spte.  Later
> -        * page faults will create the large-page sptes.
> +        * Reset each vcpu's mmu, then page faults will create the large-page
> +        * sptes later.
>          */
>         if ((change != KVM_MR_DELETE) &&
>                 (old->flags & KVM_MEM_LOG_DIRTY_PAGES) &&
> -               !(new->flags & KVM_MEM_LOG_DIRTY_PAGES))
> -               kvm_mmu_zap_collapsible_sptes(kvm, new);
> +               !(new->flags & KVM_MEM_LOG_DIRTY_PAGES)) {
> +               kvm_for_each_vcpu(i, vcpu, kvm)
> +                       kvm_mmu_reset_context(vcpu);

This should be "kvm_make_all_cpus_request(kvm, KVM_REQ_MMU_RELOAD);" but
I am not sure it is enough.  I think that if you do not zap the SPTEs,
the page faults will use 4K SPTEs, not large ones (though I'd have to
check better; CCing Xiao and Wanpeng).

Paolo