Re: [RFC PATCH 1/5] KVM: Split tdp_mmu_pages to private and shared lists

[Zhi Wang <zhi.wang.linux@gmail.com>]

On Fri,  7 Apr 2023 20:19:17 +0000
Sagi Shahar <sagis@google.com> wrote:

This patch is actually adding a separate counter for accounting private
tdp mmu page not really introducing a new tdp_mmu_pages list for private
pages. I guess better refine the tittle to reflect what this patch
is doing.

> tdp_mmu_pages holds all the active pages used by the mmu. When we
> transfer the state during intra-host migration we need to transfer the
> private pages but not the shared ones.
> 
Maybe explain a little bit about how the shared one is processed. Guess
one sentence is enough.
> Keeping them in separate counters makes this transfer more efficient.
> 
> Signed-off-by: Sagi Shahar <sagis@google.com>
> ---
>  arch/x86/include/asm/kvm_host.h |  5 ++++-
>  arch/x86/kvm/mmu/tdp_mmu.c      | 11 +++++++++--
>  2 files changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index ae377eec81987..5ed70cd9d74bf 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1426,9 +1426,12 @@ struct kvm_arch {
>  	struct task_struct *nx_huge_page_recovery_thread;
>  
>  #ifdef CONFIG_X86_64
> -	/* The number of TDP MMU pages across all roots. */
> +	/* The number of non-private TDP MMU pages across all roots. */
>  	atomic64_t tdp_mmu_pages;
>  
> +	/* Same as tdp_mmu_pages but only for private pages. */
> +	atomic64_t tdp_private_mmu_pages;
> +
>  	/*
>  	 * List of struct kvm_mmu_pages being used as roots.
>  	 * All struct kvm_mmu_pages in the list should have
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index 58a236a69ec72..327dee4f6170e 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -44,6 +44,7 @@ void kvm_mmu_uninit_tdp_mmu(struct kvm *kvm)
>  	destroy_workqueue(kvm->arch.tdp_mmu_zap_wq);
>  
>  	WARN_ON(atomic64_read(&kvm->arch.tdp_mmu_pages));
> +	WARN_ON(atomic64_read(&kvm->arch.tdp_private_mmu_pages));
>  	WARN_ON(!list_empty(&kvm->arch.tdp_mmu_roots));
>  
>  	/*
> @@ -373,13 +374,19 @@ static void handle_changed_spte_dirty_log(struct kvm *kvm, int as_id, gfn_t gfn,
>  static void tdp_account_mmu_page(struct kvm *kvm, struct kvm_mmu_page *sp)
>  {
>  	kvm_account_pgtable_pages((void *)sp->spt, +1);
> -	atomic64_inc(&kvm->arch.tdp_mmu_pages);
> +	if (is_private_sp(sp))
> +		atomic64_inc(&kvm->arch.tdp_private_mmu_pages);
> +	else
> +		atomic64_inc(&kvm->arch.tdp_mmu_pages);
>  }
>  
>  static void tdp_unaccount_mmu_page(struct kvm *kvm, struct kvm_mmu_page *sp)
>  {
>  	kvm_account_pgtable_pages((void *)sp->spt, -1);
> -	atomic64_dec(&kvm->arch.tdp_mmu_pages);
> +	if (is_private_sp(sp))
> +		atomic64_dec(&kvm->arch.tdp_private_mmu_pages);
> +	else
> +		atomic64_dec(&kvm->arch.tdp_mmu_pages);
>  }
>  
>  /**