Re: [Patch v3 4/7] KVM: x86/mmu: Optimize SPTE change for aging gfn range

David Matlack
2023-02-15T21:15:26Z

On Fri, Feb 10, 2023 at 05:46:23PM -0800, Vipin Sharma wrote:
> No need to check all of the conditions in __handle_changed_spte(). Aging
> a gfn range implies resetting access bit or marking spte for access
> tracking.

nit: State what the patch does first.

>
> Use atomic operation to only reset those bits. This avoids checking many
> conditions in __handle_changed_spte() API. Also, clean up code by
> removing dead code and API parameters.
>
> Signed-off-by: Vipin Sharma <vipinsh@google.com>

nits aside,

Reviewed-by: David Matlack <dmatlack@google.com>

> ---
> arch/x86/kvm/mmu/tdp_mmu.c | 36 +++++++++++++++++++-----------------
> 1 file changed, 19 insertions(+), 17 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index c895560244de..5d6e77554797 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -758,13 +758,6 @@ static inline void tdp_mmu_set_spte(struct kvm *kvm, struct tdp_iter *iter,
> _tdp_mmu_set_spte(kvm, iter, new_spte, true);
> }
>
> -static inline void tdp_mmu_set_spte_no_acc_track(struct kvm *kvm,
> - struct tdp_iter *iter,
> - u64 new_spte)
> -{
> - _tdp_mmu_set_spte(kvm, iter, new_spte, false);
> -}
> -
> #define tdp_root_for_each_pte(_iter, _root, _start, _end) \
> for_each_tdp_pte(_iter, _root, _start, _end)
>
> @@ -1251,32 +1244,41 @@ static __always_inline bool kvm_tdp_mmu_handle_gfn(struct kvm *kvm,
> /*
> * Mark the SPTEs range of GFNs [start, end) unaccessed and return non-zero
> * if any of the GFNs in the range have been accessed.
> + *
> + * No need to mark corresponding PFN as accessed as this call is coming from
> + * the clear_young() or clear_flush_young() notifier, which uses the return
> + * value to determine if the page has been accessed.
> */
> static bool age_gfn_range(struct kvm *kvm, struct tdp_iter *iter,
> struct kvm_gfn_range *range)
> {
> - u64 new_spte = 0;
> + u64 new_spte;
>
> /* If we have a non-accessed entry we don't need to change the pte. */
> if (!is_accessed_spte(iter->old_spte))
> return false;
>
> - new_spte = iter->old_spte;
> -
> - if (spte_ad_enabled(new_spte)) {
> - new_spte &= ~shadow_accessed_mask;
> + if (spte_ad_enabled(iter->old_spte)) {
> + iter->old_spte = tdp_mmu_clear_spte_bits(iter->sptep,

nit: Extra space before =