Re: [Patch v4 03/18] KVM: x86/mmu: Track count of pages in KVM MMU page caches globally

From: Zhi Wang
Date: Thu Mar 09 2023 - 10:37:21 EST

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In reply to: Vipin Sharma: "Re: [Patch v4 03/18] KVM: x86/mmu: Track count of pages in KVM MMU page caches globally"
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On Mon, 6 Mar 2023 14:41:12 -0800
Vipin Sharma <vipinsh@xxxxxxxxxx> wrote:

> Create a global counter for total number of pages available
> in MMU page caches across all VMs. Add mmu_shadow_page_cache
> pages to this counter.
>
> This accounting will be used in future commits to shrink MMU caches via
> KVM MMU shrinker.
>
> Signed-off-by: Vipin Sharma <vipinsh@xxxxxxxxxx>
> ---
> arch/x86/include/asm/kvm_host.h | 5 ++
> arch/x86/kvm/mmu/mmu.c | 90 ++++++++++++++++++++++++++++-----
> arch/x86/kvm/mmu/mmu_internal.h | 2 +
> arch/x86/kvm/mmu/paging_tmpl.h | 25 +++++----
> arch/x86/kvm/mmu/tdp_mmu.c | 3 +-
> 5 files changed, 100 insertions(+), 25 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index ebbe692acf3f..4322c7020d5d 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -791,6 +791,11 @@ struct kvm_vcpu_arch {
> struct kvm_mmu_memory_cache mmu_shadowed_info_cache;
> struct kvm_mmu_memory_cache mmu_page_header_cache;
>
> + /*
> + * Protect allocation and release of pages from mmu_shadow_page_cache.
> + */
> + struct mutex mmu_shadow_page_cache_lock;
> +
> /*
> * QEMU userspace and the guest each have their own FPU state.
> * In vcpu_run, we switch between the user and guest FPU contexts.
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 3a452989f5cd..13f41b7ac280 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -167,6 +167,11 @@ struct kvm_shadow_walk_iterator {
> static struct kmem_cache *pte_list_desc_cache;
> struct kmem_cache *mmu_page_header_cache;
>
> +/*
> + * Global count of unused pages in MMU page caches across all VMs.
> + */
> +static struct percpu_counter kvm_total_unused_cached_pages;
> +
> static void mmu_spte_set(u64 *sptep, u64 spte);
>
> struct kvm_mmu_role_regs {
> @@ -667,6 +672,34 @@ static void walk_shadow_page_lockless_end(struct kvm_vcpu *vcpu)
> }
> }
>
> +/**
> + * Caller should hold mutex lock corresponding to cache, if available.
> + */
> +static int mmu_topup_sp_memory_cache(struct kvm_mmu_memory_cache *cache,
> + int min)
> +{
> + int orig_nobjs, r;
> +
> + orig_nobjs = cache->nobjs;
> + r = kvm_mmu_topup_memory_cache(cache, min);
> + if (orig_nobjs != cache->nobjs)
> + percpu_counter_add(&kvm_total_unused_cached_pages,
> + (cache->nobjs - orig_nobjs));
> +
> + return r;
> +}
> +
> +/**
> + * Caller should hold mutex lock corresponding to kvm_mmu_memory_cache, if
> + * available.
> + */
> +static void mmu_free_sp_memory_cache(struct kvm_mmu_memory_cache *cache)
> +{
> + if (cache->nobjs)
> + percpu_counter_sub(&kvm_total_unused_cached_pages, cache->nobjs);
> + kvm_mmu_free_memory_cache(cache);
> +}
> +
> static int mmu_topup_memory_caches(struct kvm_vcpu *vcpu, bool maybe_indirect)
> {
> int r;
> @@ -676,10 +709,11 @@ static int mmu_topup_memory_caches(struct kvm_vcpu *vcpu, bool maybe_indirect)
> 1 + PT64_ROOT_MAX_LEVEL + PTE_PREFETCH_NUM);
> if (r)
> return r;
> - r = kvm_mmu_topup_memory_cache(&vcpu->arch.mmu_shadow_page_cache,
> - PT64_ROOT_MAX_LEVEL);
> +
> + r = mmu_topup_sp_memory_cache(&vcpu->arch.mmu_shadow_page_cache, PT64_ROOT_MAX_LEVEL);
> if (r)
> return r;
> +
> if (maybe_indirect) {
> r = kvm_mmu_topup_memory_cache(&vcpu->arch.mmu_shadowed_info_cache,
> PT64_ROOT_MAX_LEVEL);
> @@ -693,7 +727,9 @@ static int mmu_topup_memory_caches(struct kvm_vcpu *vcpu, bool maybe_indirect)
> static void mmu_free_memory_caches(struct kvm_vcpu *vcpu)
> {
> kvm_mmu_free_memory_cache(&vcpu->arch.mmu_pte_list_desc_cache);
> - kvm_mmu_free_memory_cache(&vcpu->arch.mmu_shadow_page_cache);
> + mutex_lock(&vcpu->arch.mmu_shadow_page_cache_lock);
> + mmu_free_sp_memory_cache(&vcpu->arch.mmu_shadow_page_cache);
> + mutex_unlock(&vcpu->arch.mmu_shadow_page_cache_lock);
> kvm_mmu_free_memory_cache(&vcpu->arch.mmu_shadowed_info_cache);
> kvm_mmu_free_memory_cache(&vcpu->arch.mmu_page_header_cache);
> }
> @@ -2148,6 +2184,7 @@ struct shadow_page_caches {
> struct kvm_mmu_memory_cache *page_header_cache;
> struct kvm_mmu_memory_cache *shadow_page_cache;
> struct kvm_mmu_memory_cache *shadowed_info_cache;
> + bool count_shadow_page_allocation;
> };
>
> static struct kvm_mmu_page *kvm_mmu_alloc_shadow_page(struct kvm *kvm,
> @@ -2159,7 +2196,8 @@ static struct kvm_mmu_page *kvm_mmu_alloc_shadow_page(struct kvm *kvm,
> struct kvm_mmu_page *sp;
>
> sp = kvm_mmu_memory_cache_alloc(caches->page_header_cache);
> - sp->spt = kvm_mmu_memory_cache_alloc(caches->shadow_page_cache);
> + sp->spt = mmu_sp_memory_cache_alloc(caches->shadow_page_cache,
> + caches->count_shadow_page_allocation);
> if (!role.direct)
> sp->shadowed_translation = kvm_mmu_memory_cache_alloc(caches->shadowed_info_cache);
>
> @@ -2216,6 +2254,7 @@ static struct kvm_mmu_page *kvm_mmu_get_shadow_page(struct kvm_vcpu *vcpu,
> .page_header_cache = &vcpu->arch.mmu_page_header_cache,
> .shadow_page_cache = &vcpu->arch.mmu_shadow_page_cache,
> .shadowed_info_cache = &vcpu->arch.mmu_shadowed_info_cache,
> + .count_shadow_page_allocation = true,
> };
>
> return __kvm_mmu_get_shadow_page(vcpu->kvm, vcpu, &caches, gfn, role);
> @@ -4314,29 +4353,32 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
> if (r != RET_PF_INVALID)
> return r;
>
> + mutex_lock(&vcpu->arch.mmu_shadow_page_cache_lock);
> r = mmu_topup_memory_caches(vcpu, false);
> if (r)
> - return r;
> + goto out_page_cache_unlock;
>
> r = kvm_faultin_pfn(vcpu, fault, ACC_ALL);
> if (r != RET_PF_CONTINUE)
> - return r;
> + goto out_page_cache_unlock;
>
> r = RET_PF_RETRY;
> write_lock(&vcpu->kvm->mmu_lock);
>
> if (is_page_fault_stale(vcpu, fault))
> - goto out_unlock;
> + goto out_mmu_unlock;
>
> r = make_mmu_pages_available(vcpu);
> if (r)
> - goto out_unlock;
> + goto out_mmu_unlock;
>
> r = direct_map(vcpu, fault);
>
> -out_unlock:
> +out_mmu_unlock:
> write_unlock(&vcpu->kvm->mmu_lock);
> kvm_release_pfn_clean(fault->pfn);
> +out_page_cache_unlock:
> + mutex_unlock(&vcpu->arch.mmu_shadow_page_cache_lock);
> return r;
> }
>
> @@ -4396,25 +4438,28 @@ static int kvm_tdp_mmu_page_fault(struct kvm_vcpu *vcpu,
> if (r != RET_PF_INVALID)
> return r;
>
> + mutex_lock(&vcpu->arch.mmu_shadow_page_cache_lock);
> r = mmu_topup_memory_caches(vcpu, false);
> if (r)
> - return r;
> + goto out_page_cache_unlock;
>
> r = kvm_faultin_pfn(vcpu, fault, ACC_ALL);
> if (r != RET_PF_CONTINUE)
> - return r;
> + goto out_page_cache_unlock;
>
> r = RET_PF_RETRY;
> read_lock(&vcpu->kvm->mmu_lock);
>
> if (is_page_fault_stale(vcpu, fault))
> - goto out_unlock;
> + goto out_mmu_unlock;
>
> r = kvm_tdp_mmu_map(vcpu, fault);
>
> -out_unlock:
> +out_mmu_unlock:
> read_unlock(&vcpu->kvm->mmu_lock);
> kvm_release_pfn_clean(fault->pfn);
> +out_page_cache_unlock:
> + mutex_unlock(&vcpu->arch.mmu_shadow_page_cache_lock);
> return r;
> }
> #endif
> @@ -5394,6 +5439,7 @@ int kvm_mmu_load(struct kvm_vcpu *vcpu)
> {
> int r;
>
> + mutex_lock(&vcpu->arch.mmu_shadow_page_cache_lock);
> r = mmu_topup_memory_caches(vcpu, !vcpu->arch.mmu->root_role.direct);
> if (r)
> goto out;
> @@ -5420,6 +5466,7 @@ int kvm_mmu_load(struct kvm_vcpu *vcpu)
> */
> static_call(kvm_x86_flush_tlb_current)(vcpu);
> out:
> + mutex_unlock(&vcpu->arch.mmu_shadow_page_cache_lock);
> return r;
> }
>
> @@ -5924,6 +5971,7 @@ int kvm_mmu_create(struct kvm_vcpu *vcpu)
> vcpu->arch.mmu_page_header_cache.gfp_zero = __GFP_ZERO;
>
> vcpu->arch.mmu_shadow_page_cache.gfp_zero = __GFP_ZERO;
> + mutex_init(&vcpu->arch.mmu_shadow_page_cache_lock);
>
> vcpu->arch.mmu = &vcpu->arch.root_mmu;
> vcpu->arch.walk_mmu = &vcpu->arch.root_mmu;
> @@ -6769,12 +6817,17 @@ int kvm_mmu_vendor_module_init(void)
> if (!mmu_page_header_cache)
> goto out;
>
> + if (percpu_counter_init(&kvm_total_unused_cached_pages, 0, GFP_KERNEL))
> + goto out;
> +
> ret = register_shrinker(&mmu_shrinker, "x86-mmu");
> if (ret)
> - goto out;
> + goto out_shrinker;
>
> return 0;
>
> +out_shrinker:
> + percpu_counter_destroy(&kvm_total_unused_cached_pages);
> out:
> mmu_destroy_caches();
> return ret;
> @@ -6792,6 +6845,7 @@ void kvm_mmu_vendor_module_exit(void)
> {
> mmu_destroy_caches();
> unregister_shrinker(&mmu_shrinker);
> + percpu_counter_destroy(&kvm_total_unused_cached_pages);
> }
>
> /*
> @@ -6994,3 +7048,11 @@ void kvm_mmu_pre_destroy_vm(struct kvm *kvm)
> if (kvm->arch.nx_huge_page_recovery_thread)
> kthread_stop(kvm->arch.nx_huge_page_recovery_thread);
> }
> +
> +void *mmu_sp_memory_cache_alloc(struct kvm_mmu_memory_cache *shadow_page_cache,
> + bool count_allocation)

Is it necessary to have the control of count_allocation in every call of
mmu_sp_memory_cache_alloc() instead of taking
shadow_page_cache->count_shadow_page_allocation directly?

> +{
> + if (count_allocation && shadow_page_cache->nobjs)
> + percpu_counter_dec(&kvm_total_unused_cached_pages);
> + return kvm_mmu_memory_cache_alloc(shadow_page_cache);
> +}
> diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
> index cc58631e2336..798cfbf0a36b 100644
> --- a/arch/x86/kvm/mmu/mmu_internal.h
> +++ b/arch/x86/kvm/mmu/mmu_internal.h
> @@ -338,5 +338,7 @@ void *mmu_memory_cache_alloc(struct kvm_mmu_memory_cache *mc);
>
> void track_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp);
> void untrack_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp);
> +void *mmu_sp_memory_cache_alloc(struct kvm_mmu_memory_cache *cache,
> + bool count_allocation);
>
> #endif /* __KVM_X86_MMU_INTERNAL_H */
> diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
> index 57f0b75c80f9..1dea9be6849d 100644
> --- a/arch/x86/kvm/mmu/paging_tmpl.h
> +++ b/arch/x86/kvm/mmu/paging_tmpl.h
> @@ -821,9 +821,10 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
> return RET_PF_EMULATE;
> }
>
> + mutex_lock(&vcpu->arch.mmu_shadow_page_cache_lock);
> r = mmu_topup_memory_caches(vcpu, true);
> if (r)
> - return r;
> + goto out_page_cache_unlock;
>
> vcpu->arch.write_fault_to_shadow_pgtable = false;
>
> @@ -837,7 +838,7 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
>
> r = kvm_faultin_pfn(vcpu, fault, walker.pte_access);
> if (r != RET_PF_CONTINUE)
> - return r;
> + goto out_page_cache_unlock;
>
> /*
> * Do not change pte_access if the pfn is a mmio page, otherwise
> @@ -862,16 +863,18 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
> write_lock(&vcpu->kvm->mmu_lock);
>
> if (is_page_fault_stale(vcpu, fault))
> - goto out_unlock;
> + goto out_mmu_unlock;
>
> r = make_mmu_pages_available(vcpu);
> if (r)
> - goto out_unlock;
> + goto out_mmu_unlock;
> r = FNAME(fetch)(vcpu, fault, &walker);
>
> -out_unlock:
> +out_mmu_unlock:
> write_unlock(&vcpu->kvm->mmu_lock);
> kvm_release_pfn_clean(fault->pfn);
> +out_page_cache_unlock:
> + mutex_unlock(&vcpu->arch.mmu_shadow_page_cache_lock);
> return r;
> }
>
> @@ -897,17 +900,18 @@ static void FNAME(invlpg)(struct kvm_vcpu *vcpu, gva_t gva, hpa_t root_hpa)
>
> vcpu_clear_mmio_info(vcpu, gva);
>
> + if (!VALID_PAGE(root_hpa)) {
> + WARN_ON(1);
> + return;
> + }
> +
> + mutex_lock(&vcpu->arch.mmu_shadow_page_cache_lock);
> /*
> * No need to check return value here, rmap_can_add() can
> * help us to skip pte prefetch later.
> */
> mmu_topup_memory_caches(vcpu, true);
>
> - if (!VALID_PAGE(root_hpa)) {
> - WARN_ON(1);
> - return;
> - }
> -
> write_lock(&vcpu->kvm->mmu_lock);
> for_each_shadow_entry_using_root(vcpu, root_hpa, gva, iterator) {
> level = iterator.level;
> @@ -943,6 +947,7 @@ static void FNAME(invlpg)(struct kvm_vcpu *vcpu, gva_t gva, hpa_t root_hpa)
> break;
> }
> write_unlock(&vcpu->kvm->mmu_lock);
> + mutex_unlock(&vcpu->arch.mmu_shadow_page_cache_lock);
> }
>
> /* Note, @addr is a GPA when gva_to_gpa() translates an L2 GPA to an L1 GPA. */
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index 7c25dbf32ecc..fa6eb1e9101e 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -265,7 +265,8 @@ static struct kvm_mmu_page *tdp_mmu_alloc_sp(struct kvm_vcpu *vcpu)
> struct kvm_mmu_page *sp;
>
> sp = kvm_mmu_memory_cache_alloc(&vcpu->arch.mmu_page_header_cache);
> - sp->spt = kvm_mmu_memory_cache_alloc(&vcpu->arch.mmu_shadow_page_cache);
> + sp->spt = mmu_sp_memory_cache_alloc(&vcpu->arch.mmu_shadow_page_cache,
> + true);
>
> return sp;
> }

Next message: Peter Zijlstra: "Re: [PATCH 10/10] sched/fair: Implement an EEVDF like policy"
Previous message: Petr Mladek: "naming: Re: [PATCH printk v1 05/18] printk: Add non-BKL console basic infrastructure"
In reply to: Vipin Sharma: "Re: [Patch v4 03/18] KVM: x86/mmu: Track count of pages in KVM MMU page caches globally"
Next in thread: Vipin Sharma: "Re: [Patch v4 03/18] KVM: x86/mmu: Track count of pages in KVM MMU page caches globally"
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