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Keep shrinker infrastructure in place to reuse in future commits for freeing KVM page caches. Remove zapped_obsolete_pages list from struct kvm_arch{} and use local list in kvm_zap_obsolete_pages() since MMU shrinker is not using it anymore. mmu_shrink_scan() is very disruptive to VMs. It picks the first VM in the vm_list, zaps the oldest page which is most likely an upper level SPTEs and most like to be reused. Prior to TDP MMU, this is even more disruptive in nested VMs case, considering L1 SPTEs will be the oldest even though most of the entries are for L2 SPTEs. As discussed in https://lore.kernel.org/lkml/Y45dldZnI6OIf+a5@google.com/ shrinker logic has not be very useful in actually keeping VMs performant and reducing memory usage. Suggested-by: Sean Christopherson Suggested-by: David Matlack Signed-off-by: Vipin Sharma Reviewed-by: David Matlack --- arch/x86/include/asm/kvm_host.h | 1 - arch/x86/kvm/mmu/mmu.c | 92 +++------------------------------ 2 files changed, 8 insertions(+), 85 deletions(-) diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index b0c0bc0ed813..cbfe31bac6cf 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -1309,7 +1309,6 @@ struct kvm_arch { bool pre_fault_allowed; struct hlist_head mmu_page_hash[KVM_NUM_MMU_PAGES]; struct list_head active_mmu_pages; - struct list_head zapped_obsolete_pages; /* * A list of kvm_mmu_page structs that, if zapped, could possibly be * replaced by an NX huge page. A shadow page is on this list if its diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index d25c2b395116..213e46b55dda 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -179,7 +179,6 @@ struct kvm_shadow_walk_iterator { static struct kmem_cache *pte_list_desc_cache; struct kmem_cache *mmu_page_header_cache; -static struct percpu_counter kvm_total_used_mmu_pages; static void mmu_spte_set(u64 *sptep, u64 spte); @@ -1651,27 +1650,15 @@ static void kvm_mmu_check_sptes_at_free(struct kvm_mmu_page *sp) #endif } -/* - * This value is the sum of all of the kvm instances's - * kvm->arch.n_used_mmu_pages values. We need a global, - * aggregate version in order to make the slab shrinker - * faster - */ -static inline void kvm_mod_used_mmu_pages(struct kvm *kvm, long nr) -{ - kvm->arch.n_used_mmu_pages += nr; - percpu_counter_add(&kvm_total_used_mmu_pages, nr); -} - static void kvm_account_mmu_page(struct kvm *kvm, struct kvm_mmu_page *sp) { - kvm_mod_used_mmu_pages(kvm, +1); + kvm->arch.n_used_mmu_pages++; kvm_account_pgtable_pages((void *)sp->spt, +1); } static void kvm_unaccount_mmu_page(struct kvm *kvm, struct kvm_mmu_page *sp) { - kvm_mod_used_mmu_pages(kvm, -1); + kvm->arch.n_used_mmu_pages--; kvm_account_pgtable_pages((void *)sp->spt, -1); } @@ -6338,6 +6325,7 @@ static void kvm_zap_obsolete_pages(struct kvm *kvm) { struct kvm_mmu_page *sp, *node; int nr_zapped, batch = 0; + LIST_HEAD(invalid_list); bool unstable; restart: @@ -6371,7 +6359,7 @@ static void kvm_zap_obsolete_pages(struct kvm *kvm) } unstable = __kvm_mmu_prepare_zap_page(kvm, sp, - &kvm->arch.zapped_obsolete_pages, &nr_zapped); + &invalid_list, &nr_zapped); batch += nr_zapped; if (unstable) @@ -6387,7 +6375,7 @@ static void kvm_zap_obsolete_pages(struct kvm *kvm) * kvm_mmu_load()), and the reload in the caller ensure no vCPUs are * running with an obsolete MMU. */ - kvm_mmu_commit_zap_page(kvm, &kvm->arch.zapped_obsolete_pages); + kvm_mmu_commit_zap_page(kvm, &invalid_list); } /* @@ -6450,16 +6438,10 @@ static void kvm_mmu_zap_all_fast(struct kvm *kvm) kvm_tdp_mmu_zap_invalidated_roots(kvm); } -static bool kvm_has_zapped_obsolete_pages(struct kvm *kvm) -{ - return unlikely(!list_empty_careful(&kvm->arch.zapped_obsolete_pages)); -} - void kvm_mmu_init_vm(struct kvm *kvm) { kvm->arch.shadow_mmio_value = shadow_mmio_value; INIT_LIST_HEAD(&kvm->arch.active_mmu_pages); - INIT_LIST_HEAD(&kvm->arch.zapped_obsolete_pages); INIT_LIST_HEAD(&kvm->arch.possible_nx_huge_pages); spin_lock_init(&kvm->arch.mmu_unsync_pages_lock); @@ -7015,65 +6997,13 @@ void kvm_mmu_invalidate_mmio_sptes(struct kvm *kvm, u64 gen) static unsigned long mmu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc) { - struct kvm *kvm; - int nr_to_scan = sc->nr_to_scan; - unsigned long freed = 0; - - mutex_lock(&kvm_lock); - - list_for_each_entry(kvm, &vm_list, vm_list) { - int idx; - - /* - * Never scan more than sc->nr_to_scan VM instances. - * Will not hit this condition practically since we do not try - * to shrink more than one VM and it is very unlikely to see - * !n_used_mmu_pages so many times. - */ - if (!nr_to_scan--) - break; - /* - * n_used_mmu_pages is accessed without holding kvm->mmu_lock - * here. We may skip a VM instance errorneosly, but we do not - * want to shrink a VM that only started to populate its MMU - * anyway. - */ - if (!kvm->arch.n_used_mmu_pages && - !kvm_has_zapped_obsolete_pages(kvm)) - continue; - - idx = srcu_read_lock(&kvm->srcu); - write_lock(&kvm->mmu_lock); - - if (kvm_has_zapped_obsolete_pages(kvm)) { - kvm_mmu_commit_zap_page(kvm, - &kvm->arch.zapped_obsolete_pages); - goto unlock; - } - - freed = kvm_mmu_zap_oldest_mmu_pages(kvm, sc->nr_to_scan); - -unlock: - write_unlock(&kvm->mmu_lock); - srcu_read_unlock(&kvm->srcu, idx); - - /* - * unfair on small ones - * per-vm shrinkers cry out - * sadness comes quickly - */ - list_move_tail(&kvm->vm_list, &vm_list); - break; - } - - mutex_unlock(&kvm_lock); - return freed; + return SHRINK_STOP; } static unsigned long mmu_shrink_count(struct shrinker *shrink, struct shrink_control *sc) { - return percpu_counter_read_positive(&kvm_total_used_mmu_pages); + return SHRINK_EMPTY; } static struct shrinker *mmu_shrinker; @@ -7204,12 +7134,9 @@ int kvm_mmu_vendor_module_init(void) if (!mmu_page_header_cache) goto out; - if (percpu_counter_init(&kvm_total_used_mmu_pages, 0, GFP_KERNEL)) - goto out; - mmu_shrinker = shrinker_alloc(0, "x86-mmu"); if (!mmu_shrinker) - goto out_shrinker; + goto out; mmu_shrinker->count_objects = mmu_shrink_count; mmu_shrinker->scan_objects = mmu_shrink_scan; @@ -7219,8 +7146,6 @@ int kvm_mmu_vendor_module_init(void) return 0; -out_shrinker: - percpu_counter_destroy(&kvm_total_used_mmu_pages); out: mmu_destroy_caches(); return ret; @@ -7237,7 +7162,6 @@ void kvm_mmu_destroy(struct kvm_vcpu *vcpu) void kvm_mmu_vendor_module_exit(void) { mmu_destroy_caches(); - percpu_counter_destroy(&kvm_total_used_mmu_pages); shrinker_free(mmu_shrinker); } From patchwork Fri Sep 13 21:43:16 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Vipin Sharma X-Patchwork-Id: 13804104 Received: from mail-yb1-f201.google.com (mail-yb1-f201.google.com [209.85.219.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5176616F85E for ; 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Fri, 13 Sep 2024 14:43:35 -0700 (PDT) Date: Fri, 13 Sep 2024 14:43:16 -0700 In-Reply-To: <20240913214316.1945951-1-vipinsh@google.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240913214316.1945951-1-vipinsh@google.com> X-Mailer: git-send-email 2.46.0.662.g92d0881bb0-goog Message-ID: <20240913214316.1945951-3-vipinsh@google.com> Subject: [PATCH 2/2] KVM: x86/mmu: Use MMU shrinker to shrink KVM MMU memory caches From: Vipin Sharma To: seanjc@google.com, pbonzini@redhat.com Cc: dmatlack@google.com, zhi.wang.linux@gmail.com, weijiang.yang@intel.com, mizhang@google.com, liangchen.linux@gmail.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Vipin Sharma Use MMU shrinker to iterate through all the vCPUs of all the VMs and free pages allocated in MMU memory caches. Protect cache allocation in page fault and MMU load path from MMU shrinker by using a per vCPU mutex. In MMU shrinker, move the iterated VM to the end of the VMs list so that the pain of emptying cache spread among other VMs too. The specific caches to empty are mmu_shadow_page_cache and mmu_shadowed_info_cache as these caches store whole pages. Emptying them will give more impact to shrinker compared to other caches like mmu_pte_list_desc_cache{} and mmu_page_header_cache{} Holding per vCPU mutex lock ensures that a vCPU doesn't get surprised by finding its cache emptied after filling them up for page table allocations during page fault handling and MMU load operation. Per vCPU mutex also makes sure there is only race between MMU shrinker and all other vCPUs. This should result in very less contention. Suggested-by: Sean Christopherson Suggested-by: David Matlack Signed-off-by: Vipin Sharma --- arch/x86/include/asm/kvm_host.h | 6 +++ arch/x86/kvm/mmu/mmu.c | 69 +++++++++++++++++++++++++++------ arch/x86/kvm/mmu/paging_tmpl.h | 14 ++++--- include/linux/kvm_host.h | 1 + virt/kvm/kvm_main.c | 8 +++- 5 files changed, 81 insertions(+), 17 deletions(-) diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index cbfe31bac6cf..63eaf03111eb 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -811,6 +811,12 @@ struct kvm_vcpu_arch { */ struct kvm_mmu *walk_mmu; + /* + * Protect cache from getting emptied in MMU shrinker while vCPU might + * use cache for fault handling or loading MMU. As this is a per vCPU + * lock, only contention might happen when MMU shrinker runs. + */ + struct mutex mmu_memory_cache_lock; struct kvm_mmu_memory_cache mmu_pte_list_desc_cache; struct kvm_mmu_memory_cache mmu_shadow_page_cache; struct kvm_mmu_memory_cache mmu_shadowed_info_cache; diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 213e46b55dda..8e2935347615 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -4524,29 +4524,33 @@ 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_memory_cache_lock); r = mmu_topup_memory_caches(vcpu, false); if (r) - return r; + goto out_mmu_memory_cache_unlock; r = kvm_faultin_pfn(vcpu, fault, ACC_ALL); if (r != RET_PF_CONTINUE) - return r; + goto out_mmu_memory_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_mmu_memory_cache_unlock: + mutex_unlock(&vcpu->arch.mmu_memory_cache_lock); + return r; } @@ -4617,25 +4621,28 @@ static int kvm_tdp_mmu_page_fault(struct kvm_vcpu *vcpu, if (r != RET_PF_INVALID) return r; + mutex_lock(&vcpu->arch.mmu_memory_cache_lock); r = mmu_topup_memory_caches(vcpu, false); if (r) - return r; + goto out_mmu_memory_cache_unlock; r = kvm_faultin_pfn(vcpu, fault, ACC_ALL); if (r != RET_PF_CONTINUE) - return r; + goto out_mmu_memory_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_mmu_memory_cache_unlock: + mutex_unlock(&vcpu->arch.mmu_memory_cache_lock); return r; } #endif @@ -5691,6 +5698,7 @@ int kvm_mmu_load(struct kvm_vcpu *vcpu) { int r; + mutex_lock(&vcpu->arch.mmu_memory_cache_lock); r = mmu_topup_memory_caches(vcpu, !vcpu->arch.mmu->root_role.direct); if (r) goto out; @@ -5717,6 +5725,7 @@ int kvm_mmu_load(struct kvm_vcpu *vcpu) */ kvm_x86_call(flush_tlb_current)(vcpu); out: + mutex_unlock(&vcpu->arch.mmu_memory_cache_lock); return r; } @@ -6303,6 +6312,7 @@ int kvm_mmu_create(struct kvm_vcpu *vcpu) if (!vcpu->arch.mmu_shadow_page_cache.init_value) vcpu->arch.mmu_shadow_page_cache.gfp_zero = __GFP_ZERO; + mutex_init(&vcpu->arch.mmu_memory_cache_lock); vcpu->arch.mmu = &vcpu->arch.root_mmu; vcpu->arch.walk_mmu = &vcpu->arch.root_mmu; @@ -6997,13 +7007,50 @@ void kvm_mmu_invalidate_mmio_sptes(struct kvm *kvm, u64 gen) static unsigned long mmu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc) { - return SHRINK_STOP; + struct kvm *kvm, *next_kvm, *first_kvm = NULL; + unsigned long i, freed = 0; + struct kvm_vcpu *vcpu; + + mutex_lock(&kvm_lock); + list_for_each_entry_safe(kvm, next_kvm, &vm_list, vm_list) { + if (!first_kvm) + first_kvm = kvm; + else if (first_kvm == kvm) + break; + + list_move_tail(&kvm->vm_list, &vm_list); + + kvm_for_each_vcpu(i, vcpu, kvm) { + if (!mutex_trylock(&vcpu->arch.mmu_memory_cache_lock)) + continue; + freed += kvm_mmu_empty_memory_cache(&vcpu->arch.mmu_shadow_page_cache); + freed += kvm_mmu_empty_memory_cache(&vcpu->arch.mmu_shadowed_info_cache); + mutex_unlock(&vcpu->arch.mmu_memory_cache_lock); + if (freed >= sc->nr_to_scan) + goto out; + } + } +out: + mutex_unlock(&kvm_lock); + return freed; } static unsigned long mmu_shrink_count(struct shrinker *shrink, struct shrink_control *sc) { - return SHRINK_EMPTY; + unsigned long i, count = 0; + struct kvm_vcpu *vcpu; + struct kvm *kvm; + + mutex_lock(&kvm_lock); + list_for_each_entry(kvm, &vm_list, vm_list) { + kvm_for_each_vcpu(i, vcpu, kvm) { + count += READ_ONCE(vcpu->arch.mmu_shadow_page_cache.nobjs); + count += READ_ONCE(vcpu->arch.mmu_shadowed_info_cache.nobjs); + } + } + mutex_unlock(&kvm_lock); + return !count ? SHRINK_EMPTY : count; } static struct shrinker *mmu_shrinker; diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h index 405bd7ceee2a..084a5c532078 100644 --- a/arch/x86/kvm/mmu/paging_tmpl.h +++ b/arch/x86/kvm/mmu/paging_tmpl.h @@ -809,13 +809,14 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault return RET_PF_EMULATE; } + mutex_lock(&vcpu->arch.mmu_memory_cache_lock); r = mmu_topup_memory_caches(vcpu, true); if (r) - return r; + goto out_mmu_memory_cache_unlock; r = kvm_faultin_pfn(vcpu, fault, walker.pte_access); if (r != RET_PF_CONTINUE) - return r; + goto out_mmu_memory_cache_unlock; /* * Do not change pte_access if the pfn is a mmio page, otherwise @@ -840,16 +841,19 @@ 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_mmu_memory_cache_unlock: + mutex_unlock(&vcpu->arch.mmu_memory_cache_lock); + return r; } diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index b23c6d48392f..288e503f14a0 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -1446,6 +1446,7 @@ void kvm_flush_remote_tlbs_memslot(struct kvm *kvm, int kvm_mmu_topup_memory_cache(struct kvm_mmu_memory_cache *mc, int min); int __kvm_mmu_topup_memory_cache(struct kvm_mmu_memory_cache *mc, int capacity, int min); int kvm_mmu_memory_cache_nr_free_objects(struct kvm_mmu_memory_cache *mc); +int kvm_mmu_empty_memory_cache(struct kvm_mmu_memory_cache *mc); void kvm_mmu_free_memory_cache(struct kvm_mmu_memory_cache *mc); void *kvm_mmu_memory_cache_alloc(struct kvm_mmu_memory_cache *mc); #endif diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index cb2b78e92910..5d89ca218791 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -451,15 +451,21 @@ int kvm_mmu_memory_cache_nr_free_objects(struct kvm_mmu_memory_cache *mc) return mc->nobjs; } -void kvm_mmu_free_memory_cache(struct kvm_mmu_memory_cache *mc) +int kvm_mmu_empty_memory_cache(struct kvm_mmu_memory_cache *mc) { + int freed = mc->nobjs; while (mc->nobjs) { if (mc->kmem_cache) kmem_cache_free(mc->kmem_cache, mc->objects[--mc->nobjs]); else free_page((unsigned long)mc->objects[--mc->nobjs]); } + return freed; +} +void kvm_mmu_free_memory_cache(struct kvm_mmu_memory_cache *mc) +{ + kvm_mmu_empty_memory_cache(mc); kvfree(mc->objects); mc->objects = NULL;