[v2,19/22] KVM: MMU: lockless walking shadow page table

Message ID	4E01FDB4.60306@cn.fujitsu.com (mailing list archive)
State	New, archived
Headers	show Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by demeter1.kernel.org (8.14.4/8.14.4) with ESMTP id p5MEYAlO029398 for <patchwork-kvm@patchwork.kernel.org>; Wed, 22 Jun 2011 14:34:10 GMT Message-ID: <4E01FDB4.60306@cn.fujitsu.com> Date: Wed, 22 Jun 2011 22:35:32 +0800 From: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com> User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.17) Gecko/20110428 Fedora/3.1.10-1.fc15 Thunderbird/3.1.10 MIME-Version: 1.0 To: Avi Kivity <avi@redhat.com> CC: Marcelo Tosatti <mtosatti@redhat.com>, LKML <linux-kernel@vger.kernel.org>, KVM <kvm@vger.kernel.org> Subject: [PATCH v2 19/22] KVM: MMU: lockless walking shadow page table References: <4E01FBC9.3020009@cn.fujitsu.com> In-Reply-To: <4E01FBC9.3020009@cn.fujitsu.com> Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=UTF-8 Sender: kvm-owner@vger.kernel.org Precedence: bulk

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 42e577d..87a868e 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -233,6 +233,12 @@ struct kvm_mmu_page { unsigned int unsync_children; unsigned long parent_ptes; /* Reverse mapping for parent_pte */ DECLARE_BITMAP(unsync_child_bitmap, 512); + +#ifdef CONFIG_X86_32 + int clear_spte_count; +#endif + + struct rcu_head rcu; }; struct kvm_pv_mmu_op_buffer { @@ -477,6 +483,8 @@ struct kvm_arch { u64 hv_guest_os_id; u64 hv_hypercall; + atomic_t reader_counter; + #ifdef CONFIG_KVM_MMU_AUDIT int audit_point; #endif diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index 0ba94e9..dad7ad9 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -182,6 +182,12 @@ struct kvm_shadow_walk_iterator { shadow_walk_okay(&(_walker)); \ shadow_walk_next(&(_walker))) +#define for_each_shadow_entry_lockless(_vcpu, _addr, _walker, spte) \ + for (shadow_walk_init(&(_walker), _vcpu, _addr); \ + shadow_walk_okay(&(_walker)) && \ + ({ spte = mmu_spte_get_lockless(_walker.sptep); 1; }); \ + __shadow_walk_next(&(_walker), spte)) + static struct kmem_cache *pte_list_desc_cache; static struct kmem_cache *mmu_page_header_cache; static struct percpu_counter kvm_total_used_mmu_pages; @@ -274,6 +280,11 @@ static u64 __update_clear_spte_slow(u64 *sptep, u64 spte) { return xchg(sptep, spte); } + +static u64 __get_spte_lockless(u64 *sptep) +{ + return ACCESS_ONCE(*sptep); +} #else union split_spte { struct { @@ -283,6 +294,18 @@ union split_spte { u64 spte; }; +static void count_spte_clear(u64 *sptep, u64 spte) +{ + struct kvm_mmu_page *sp = page_header(__pa(sptep)); + + if (is_shadow_present_pte(spte)) + return; + + /* Ensure the spte is completely set before we increase the count */ + smp_wmb(); + sp->clear_spte_count++; +} + static void __set_spte(u64 *sptep, u64 spte) { union split_spte *ssptep, sspte; @@ -318,6 +341,7 @@ static void __update_clear_spte_fast(u64 *sptep, u64 spte) smp_wmb(); ssptep->spte_high = sspte.spte_high; + count_spte_clear(sptep, spte); } static u64 __update_clear_spte_slow(u64 *sptep, u64 spte) @@ -330,9 +354,40 @@ static u64 __update_clear_spte_slow(u64 *sptep, u64 spte) /* xchg acts as a barrier before the setting of the high bits */ orig.spte_low = xchg(&ssptep->spte_low, sspte.spte_low); orig.spte_high = ssptep->spte_high = sspte.spte_high; + count_spte_clear(sptep, spte); return orig.spte; } + +/* + * The idea using the light way get the spte on x86_32 guest is from + * gup_get_pte(arch/x86/mm/gup.c). + * The difference is we can not catch the spte tlb flush if we leave + * guest mode, so we emulate it by increase clear_spte_count when spte + * is cleared. + */ +static u64 __get_spte_lockless(u64 *sptep) +{ + struct kvm_mmu_page *sp = page_header(__pa(sptep)); + union split_spte spte, *orig = (union split_spte *)sptep; + int count; + +retry: + count = sp->clear_spte_count; + smp_rmb(); + + spte.spte_low = orig->spte_low; + smp_rmb(); + + spte.spte_high = orig->spte_high; + smp_rmb(); + + if (unlikely(spte.spte_low != orig->spte_low || + count != sp->clear_spte_count)) + goto retry; + + return spte.spte; +} #endif static bool spte_is_bit_cleared(u64 old_spte, u64 new_spte, u64 bit_mask) @@ -438,6 +493,28 @@ static void mmu_spte_clear_no_track(u64 *sptep) __update_clear_spte_fast(sptep, 0ull); } +static u64 mmu_spte_get_lockless(u64 *sptep) +{ + return __get_spte_lockless(sptep); +} + +static void walk_shadow_page_lockless_begin(struct kvm_vcpu *vcpu) +{ + rcu_read_lock(); + atomic_inc(&vcpu->kvm->arch.reader_counter); + + /* Increase the counter before walking shadow page table */ + smp_mb__after_atomic_inc(); +} + +static void walk_shadow_page_lockless_end(struct kvm_vcpu *vcpu) +{ + /* Decrease the counter after walking shadow page table finished */ + smp_mb__before_atomic_dec(); + atomic_dec(&vcpu->kvm->arch.reader_counter); + rcu_read_unlock(); +} + static int mmu_topup_memory_cache(struct kvm_mmu_memory_cache *cache, struct kmem_cache *base_cache, int min) { @@ -1600,17 +1677,23 @@ static bool shadow_walk_okay(struct kvm_shadow_walk_iterator *iterator) return true; } -static void shadow_walk_next(struct kvm_shadow_walk_iterator *iterator) +static void __shadow_walk_next(struct kvm_shadow_walk_iterator *iterator, + u64 spte) { - if (is_last_spte(*iterator->sptep, iterator->level)) { + if (is_last_spte(spte, iterator->level)) { iterator->level = 0; return; } - iterator->shadow_addr = *iterator->sptep & PT64_BASE_ADDR_MASK; + iterator->shadow_addr = spte & PT64_BASE_ADDR_MASK; --iterator->level; } +static void shadow_walk_next(struct kvm_shadow_walk_iterator *iterator) +{ + return __shadow_walk_next(iterator, *iterator->sptep); +} + static void link_shadow_page(u64 *sptep, struct kvm_mmu_page *sp) { u64 spte; @@ -1757,6 +1840,30 @@ static int kvm_mmu_prepare_zap_page(struct kvm *kvm, struct kvm_mmu_page *sp, return ret; } +static void kvm_mmu_isolate_pages(struct list_head *invalid_list) +{ + struct kvm_mmu_page *sp; + + list_for_each_entry(sp, invalid_list, link) + kvm_mmu_isolate_page(sp); +} + +static void free_pages_rcu(struct rcu_head *head) +{ + struct kvm_mmu_page *next, *sp; + + sp = container_of(head, struct kvm_mmu_page, rcu); + while (sp) { + if (!list_empty(&sp->link)) + next = list_first_entry(&sp->link, + struct kvm_mmu_page, link); + else + next = NULL; + kvm_mmu_free_page(sp); + sp = next; + } +} + static void kvm_mmu_commit_zap_page(struct kvm *kvm, struct list_head *invalid_list) { @@ -1767,6 +1874,14 @@ static void kvm_mmu_commit_zap_page(struct kvm *kvm, kvm_flush_remote_tlbs(kvm); + if (atomic_read(&kvm->arch.reader_counter)) { + kvm_mmu_isolate_pages(invalid_list); + sp = list_first_entry(invalid_list, struct kvm_mmu_page, link); + list_del_init(invalid_list); + call_rcu(&sp->rcu, free_pages_rcu); + return; + } + do { sp = list_first_entry(invalid_list, struct kvm_mmu_page, link); WARN_ON(!sp->role.invalid || sp->root_count); @@ -3797,16 +3912,17 @@ out: int kvm_mmu_get_spte_hierarchy(struct kvm_vcpu *vcpu, u64 addr, u64 sptes[4]) { struct kvm_shadow_walk_iterator iterator; + u64 spte; int nr_sptes = 0; - spin_lock(&vcpu->kvm->mmu_lock); - for_each_shadow_entry(vcpu, addr, iterator) { - sptes[iterator.level-1] = *iterator.sptep; + walk_shadow_page_lockless_begin(vcpu); + for_each_shadow_entry_lockless(vcpu, addr, iterator, spte) { + sptes[iterator.level-1] = spte; nr_sptes++; - if (!is_shadow_present_pte(*iterator.sptep)) + if (!is_shadow_present_pte(spte)) break; } - spin_unlock(&vcpu->kvm->mmu_lock); + walk_shadow_page_lockless_end(vcpu); return nr_sptes; }

[v2,19/22] KVM: MMU: lockless walking shadow page table

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