Re: [RFC PATCH 15/15] KVM: x86/mmu: Update page stats when splitting large pages

[Sean Christopherson <seanjc@google.com>]

On Fri, Nov 19, 2021, David Matlack wrote:
> When splitting large pages we need to update the pages stats to reflect
> all of the new pages at the lower level. We do not need to change the
> page stats for the large page that was removed as that is already
> handled tdp_mmu_set_spte_atomic.
> 
> Signed-off-by: David Matlack <dmatlack@google.com>
> ---
>  arch/x86/kvm/mmu/tdp_mmu.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index 8f60d942c789..4c313613a939 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -1299,7 +1299,12 @@ static bool tdp_mmu_split_large_page_atomic(struct kvm *kvm, struct tdp_iter *it
>  		child_sp->spt[i] = child_spte;
>  	}
>  
> -	return tdp_mmu_install_sp_atomic(kvm, iter, child_sp, false);
> +	if (!tdp_mmu_install_sp_atomic(kvm, iter, child_sp, false))
> +		return false;
> +
> +	kvm_update_page_stats(kvm, level - 1, PT64_ENT_PER_PAGE);

This should be done when tdp_mmu_split_large_page_atomic() is introduced, otherwise
this series is effectively introducing a bug and then fixing it.  At a very quick
glance, I don't see anything that would prevent squashing this in.

> +
> +	return true;
>  }
>  
>  static void tdp_mmu_split_large_pages_root(struct kvm *kvm, struct kvm_mmu_page *root,
> -- 
> 2.34.0.rc2.393.gf8c9666880-goog
>