Re: [Patch v3 8/9] KVM: x86/mmu: Make split_shadow_page_cache NUMA aware

[Ben Gardon]

On Wed, Dec 21, 2022 at 6:35 PM Vipin Sharma <vipinsh@xxxxxxxxxx> wrote:
>
> Make split_shadow_page_cache NUMA aware and allocate page table's pages
> during the split based on the underlying physical page's NUMA node.
>
> Signed-off-by: Vipin Sharma <vipinsh@xxxxxxxxxx>
> ---
>  arch/x86/include/asm/kvm_host.h |  2 +-
>  arch/x86/kvm/mmu/mmu.c          | 50 ++++++++++++++++++---------------
>  2 files changed, 29 insertions(+), 23 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index b1f319ad6f89..7b3f36ae37a4 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1410,7 +1410,7 @@ struct kvm_arch {
>          *
>          * Protected by kvm->slots_lock.
>          */
> -       struct kvm_mmu_memory_cache split_shadow_page_cache;
> +       struct kvm_mmu_memory_cache split_shadow_page_cache[MAX_NUMNODES];
>         struct kvm_mmu_memory_cache split_page_header_cache;
>
>         /*
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 511c6ef265ee..7454bfc49a51 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -6126,7 +6126,7 @@ static void kvm_mmu_invalidate_zap_pages_in_memslot(struct kvm *kvm,
>  int kvm_mmu_init_vm(struct kvm *kvm)
>  {
>         struct kvm_page_track_notifier_node *node = &kvm->arch.mmu_sp_tracker;
> -       int r;
> +       int r, nid;
>
>         INIT_LIST_HEAD(&kvm->arch.active_mmu_pages);
>         INIT_LIST_HEAD(&kvm->arch.possible_nx_huge_pages);
> @@ -6145,8 +6145,9 @@ int kvm_mmu_init_vm(struct kvm *kvm)
>         INIT_KVM_MMU_MEMORY_CACHE(&kvm->arch.split_page_header_cache,
>                                   mmu_page_header_cache, NUMA_NO_NODE);
>
> -       INIT_KVM_MMU_MEMORY_CACHE(&kvm->arch.split_shadow_page_cache,
> -                                 NULL, NUMA_NO_NODE);
> +       for_each_node(nid)

Again, assuming no one sets CONFIG_NODE_SHIFT to a ridiculous value,
it would probably be fine to initialize the entire array here since
that doesn't take any extra memory and we're not in a super hot path.

> +               INIT_KVM_MMU_MEMORY_CACHE(&kvm->arch.split_shadow_page_cache[nid],
> +                                         NULL, NUMA_NO_NODE);
>         spin_lock_init(&kvm->arch.split_shadow_page_cache_lock);
>
>         INIT_KVM_MMU_MEMORY_CACHE(&kvm->arch.split_desc_cache,
> @@ -6157,10 +6158,13 @@ int kvm_mmu_init_vm(struct kvm *kvm)
>
>  static void mmu_free_vm_memory_caches(struct kvm *kvm)
>  {
> +       int nid;
> +
>         kvm_mmu_free_memory_cache(&kvm->arch.split_desc_cache);
>         kvm_mmu_free_memory_cache(&kvm->arch.split_page_header_cache);
> -       mmu_free_sp_memory_cache(&kvm->arch.split_shadow_page_cache,
> -                                &kvm->arch.split_shadow_page_cache_lock);
> +       for_each_node(nid)

Again, could just iterate over the whole array here.

> +               mmu_free_sp_memory_cache(&kvm->arch.split_shadow_page_cache[nid],
> +                                        &kvm->arch.split_shadow_page_cache_lock);
>  }
>
>  void kvm_mmu_uninit_vm(struct kvm *kvm)
> @@ -6269,7 +6273,7 @@ static inline bool need_topup(struct kvm_mmu_memory_cache *cache, int min)
>         return kvm_mmu_memory_cache_nr_free_objects(cache) < min;
>  }
>
> -static bool need_topup_split_caches_or_resched(struct kvm *kvm)
> +static bool need_topup_split_caches_or_resched(struct kvm *kvm, int nid)
>  {
>         if (need_resched() || rwlock_needbreak(&kvm->mmu_lock))
>                 return true;
> @@ -6281,10 +6285,10 @@ static bool need_topup_split_caches_or_resched(struct kvm *kvm)
>          */
>         return need_topup(&kvm->arch.split_desc_cache, SPLIT_DESC_CACHE_MIN_NR_OBJECTS) ||
>                need_topup(&kvm->arch.split_page_header_cache, 1) ||
> -              need_topup(&kvm->arch.split_shadow_page_cache, 1);
> +              need_topup(&kvm->arch.split_shadow_page_cache[nid], 1);
>  }
>
> -static int topup_split_caches(struct kvm *kvm)
> +static int topup_split_caches(struct kvm *kvm, int nid)
>  {
>         /*
>          * Allocating rmap list entries when splitting huge pages for nested
> @@ -6314,18 +6318,21 @@ static int topup_split_caches(struct kvm *kvm)
>         if (r)
>                 return r;
>
> -       return mmu_topup_sp_memory_cache(&kvm->arch.split_shadow_page_cache,
> +       return mmu_topup_sp_memory_cache(&kvm->arch.split_shadow_page_cache[nid],
>                                          &kvm->arch.split_shadow_page_cache_lock,
>                                          1);
>  }
>
> -static struct kvm_mmu_page *shadow_mmu_get_sp_for_split(struct kvm *kvm, u64 *huge_sptep)
> +static struct kvm_mmu_page *shadow_mmu_get_sp_for_split(struct kvm *kvm,
> +                                                       u64 *huge_sptep,
> +                                                       u64 huge_spte)

These can go on the same line.

>  {
>         struct kvm_mmu_page *huge_sp = sptep_to_sp(huge_sptep);
>         struct shadow_page_caches caches = {};
>         union kvm_mmu_page_role role;
>         unsigned int access;
>         gfn_t gfn;
> +       int nid;
>
>         gfn = kvm_mmu_page_get_gfn(huge_sp, spte_index(huge_sptep));
>         access = kvm_mmu_page_get_access(huge_sp, spte_index(huge_sptep));
> @@ -6338,9 +6345,11 @@ static struct kvm_mmu_page *shadow_mmu_get_sp_for_split(struct kvm *kvm, u64 *hu
>          */
>         role = kvm_mmu_child_role(huge_sptep, /*direct=*/true, access);
>
> +       nid = kvm_pfn_to_page_table_nid(spte_to_pfn(huge_spte));
> +
>         /* Direct SPs do not require a shadowed_info_cache. */
>         caches.page_header_cache = &kvm->arch.split_page_header_cache;
> -       caches.shadow_page_cache = &kvm->arch.split_shadow_page_cache;
> +       caches.shadow_page_cache = &kvm->arch.split_shadow_page_cache[nid];
>         caches.shadow_page_cache_lock = &kvm->arch.split_shadow_page_cache_lock;
>
>         /* Safe to pass NULL for vCPU since requesting a direct SP. */
> @@ -6360,7 +6369,7 @@ static void shadow_mmu_split_huge_page(struct kvm *kvm,
>         gfn_t gfn;
>         int index;
>
> -       sp = shadow_mmu_get_sp_for_split(kvm, huge_sptep);
> +       sp = shadow_mmu_get_sp_for_split(kvm, huge_sptep, huge_spte);
>
>         for (index = 0; index < SPTE_ENT_PER_PAGE; index++) {
>                 sptep = &sp->spt[index];
> @@ -6398,7 +6407,7 @@ static int shadow_mmu_try_split_huge_page(struct kvm *kvm,
>                                           u64 *huge_sptep)
>  {
>         struct kvm_mmu_page *huge_sp = sptep_to_sp(huge_sptep);
> -       int level, r = 0;
> +       int level, r = 0, nid;
>         gfn_t gfn;
>         u64 spte;
>
> @@ -6406,13 +6415,14 @@ static int shadow_mmu_try_split_huge_page(struct kvm *kvm,
>         gfn = kvm_mmu_page_get_gfn(huge_sp, spte_index(huge_sptep));
>         level = huge_sp->role.level;
>         spte = *huge_sptep;
> +       nid = kvm_pfn_to_page_table_nid(spte_to_pfn(spte));
>
>         if (kvm_mmu_available_pages(kvm) <= KVM_MIN_FREE_MMU_PAGES) {
>                 r = -ENOSPC;
>                 goto out;
>         }
>
> -       if (need_topup_split_caches_or_resched(kvm)) {
> +       if (need_topup_split_caches_or_resched(kvm, nid)) {
>                 write_unlock(&kvm->mmu_lock);
>                 cond_resched();
>                 /*
> @@ -6420,7 +6430,7 @@ static int shadow_mmu_try_split_huge_page(struct kvm *kvm,
>                  * rmap iterator should be restarted because the MMU lock was
>                  * dropped.
>                  */
> -               r = topup_split_caches(kvm) ?: -EAGAIN;
> +               r = topup_split_caches(kvm, nid) ?: -EAGAIN;
>                 write_lock(&kvm->mmu_lock);
>                 goto out;
>         }
> @@ -6709,17 +6719,15 @@ void kvm_mmu_invalidate_mmio_sptes(struct kvm *kvm, u64 gen)
>  }
>
>  static unsigned long mmu_shrink_cache(struct kvm_mmu_memory_cache *cache,
> -                                     int cache_count,
>                                       spinlock_t *cache_lock)
>  {
>         unsigned long freed = 0;
>         int nid;
>
>         spin_lock(cache_lock);
> -       for (nid = 0; nid < cache_count; nid++) {
> -               if (node_online(nid) && cache[nid].nobjs)
> +       for_each_online_node(nid)
> +               if (cache[nid].nobjs)
>                         freed += kvm_mmu_empty_memory_cache(&cache[nid]);
> -       }
>         spin_unlock(cache_lock);
>         return freed;
>  }
> @@ -6741,8 +6749,7 @@ mmu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
>                         first_kvm = kvm;
>                 list_move_tail(&kvm->vm_list, &vm_list);
>
> -               freed += mmu_shrink_cache(&kvm->arch.split_shadow_page_cache,
> -                                         1,
> +               freed += mmu_shrink_cache(kvm->arch.split_shadow_page_cache,
>                                           &kvm->arch.split_shadow_page_cache_lock);
>
>                 if (freed >= sc->nr_to_scan)
> @@ -6750,7 +6757,6 @@ mmu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
>
>                 kvm_for_each_vcpu(i, vcpu, kvm) {
>                         freed += mmu_shrink_cache(vcpu->arch.mmu_shadow_page_cache,
> -                                                 MAX_NUMNODES,
>                                                   &vcpu->arch.mmu_shadow_page_cache_lock);
>                 }
>
> --
> 2.39.0.314.g84b9a713c41-goog
>