Re: [Patch v2 2/5] KVM: x86/mmu: Optimize SPTE change flow for clear-dirty-log

David Matlack
2023-02-06T23:53:53Z

On Fri, Feb 3, 2023 at 11:28 AM Vipin Sharma <vipinsh@google.com> wrote:
>
> diff --git a/arch/x86/kvm/mmu/tdp_iter.h b/arch/x86/kvm/mmu/tdp_iter.h
> index 30a52e5e68de..21046b34f94e 100644
> --- a/arch/x86/kvm/mmu/tdp_iter.h
> +++ b/arch/x86/kvm/mmu/tdp_iter.h
> @@ -121,4 +121,17 @@ void tdp_iter_start(struct tdp_iter *iter, struct kvm_mmu_page *root,
> void tdp_iter_next(struct tdp_iter *iter);
> void tdp_iter_restart(struct tdp_iter *iter);
>
> +static inline u64 kvm_tdp_mmu_clear_spte_bit(struct tdp_iter *iter, u64 mask)
> +{
> + atomic64_t *sptep;
> +
> + if (kvm_tdp_mmu_spte_has_volatile_bits(iter->old_spte, iter->level)) {
> + sptep = (atomic64_t *)rcu_dereference(iter->sptep);
> + return (u64)atomic64_fetch_and(~mask, sptep);

I think you can just set iter->old_spte here and drop the return value?

> + }
> +
> + __kvm_tdp_mmu_write_spte(iter->sptep, iter->old_spte & ~mask);
> + return iter->old_spte;
> +}