Re: [PATCH v2 20/27] KVM: x86/mmu: Use page-track notifiers iff there are external users

[Yan Zhao <yan.y.zhao@intel.com>]

On Fri, Mar 10, 2023 at 04:22:51PM -0800, Sean Christopherson wrote:
> Disable the page-track notifier code at compile time if there are no
> external users, i.e. if CONFIG_KVM_EXTERNAL_WRITE_TRACKING=n.  KVM itself
> now hooks emulated writes directly instead of relying on the page-track
> mechanism.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>  arch/x86/include/asm/kvm_host.h       |  2 ++
>  arch/x86/include/asm/kvm_page_track.h |  2 ++
>  arch/x86/kvm/mmu/page_track.c         |  9 ++++-----
>  arch/x86/kvm/mmu/page_track.h         | 29 +++++++++++++++++++++++----
>  4 files changed, 33 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 1a4225237564..a3423711e403 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1265,7 +1265,9 @@ struct kvm_arch {
>  	 * create an NX huge page (without hanging the guest).
>  	 */
>  	struct list_head possible_nx_huge_pages;
> +#ifdef CONFIG_KVM_EXTERNAL_WRITE_TRACKING
>  	struct kvm_page_track_notifier_head track_notifier_head;
> +#endif
>  	/*
>  	 * Protects marking pages unsync during page faults, as TDP MMU page
>  	 * faults only take mmu_lock for read.  For simplicity, the unsync
> diff --git a/arch/x86/include/asm/kvm_page_track.h b/arch/x86/include/asm/kvm_page_track.h
> index deece45936a5..53c2adb25a07 100644
> --- a/arch/x86/include/asm/kvm_page_track.h
> +++ b/arch/x86/include/asm/kvm_page_track.h
The "#ifdef CONFIG_KVM_EXTERNAL_WRITE_TRACKING" can be moved to the
front of this file?
All the structures are only exposed for external users now.

> @@ -55,6 +55,7 @@ void kvm_slot_page_track_remove_page(struct kvm *kvm,
>  				     struct kvm_memory_slot *slot, gfn_t gfn,
>  				     enum kvm_page_track_mode mode);
>  
> +#ifdef CONFIG_KVM_EXTERNAL_WRITE_TRACKING
>  enum pg_level kvm_page_track_max_mapping_level(struct kvm *kvm, gfn_t gfn,
>  					       enum pg_level max_level);
>  
> @@ -64,5 +65,6 @@ kvm_page_track_register_notifier(struct kvm *kvm,
>  void
>  kvm_page_track_unregister_notifier(struct kvm *kvm,
>  				   struct kvm_page_track_notifier_node *n);
> +#endif /* CONFIG_KVM_EXTERNAL_WRITE_TRACKING */
>  
>  #endif