Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935772Ab3IEKb5 (ORCPT ); Thu, 5 Sep 2013 06:31:57 -0400 Received: from e23smtp01.au.ibm.com ([202.81.31.143]:58576 "EHLO e23smtp01.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935688Ab3IEK3q (ORCPT ); Thu, 5 Sep 2013 06:29:46 -0400 From: Xiao Guangrong To: gleb@redhat.com Cc: avi.kivity@gmail.com, mtosatti@redhat.com, pbonzini@redhat.com, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Xiao Guangrong Subject: [PATCH v2 09/15] KVM: MMU: introduce pte-list lockless walker Date: Thu, 5 Sep 2013 18:29:12 +0800 Message-Id: <1378376958-27252-10-git-send-email-xiaoguangrong@linux.vnet.ibm.com> X-Mailer: git-send-email 1.8.1.4 In-Reply-To: <1378376958-27252-1-git-send-email-xiaoguangrong@linux.vnet.ibm.com> References: <1378376958-27252-1-git-send-email-xiaoguangrong@linux.vnet.ibm.com> X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13090510-1618-0000-0000-0000049321A6 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3853 Lines: 126 The basic idea is from nulls list which uses a nulls to indicate whether the desc is moved to different pte-list Note, we should do bottom-up walk in the desc since we always move the bottom entry to the deleted position. A desc only has 3 entries in the current code so it is not a problem now, but the issue will be triggered if we expend the size of desc in the further development Thanks to SLAB_DESTROY_BY_RCU, the desc can be quickly reused Signed-off-by: Xiao Guangrong --- arch/x86/kvm/mmu.c | 57 ++++++++++++++++++++++++++++++++++++++++++++++++++---- 1 file changed, 53 insertions(+), 4 deletions(-) diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index c5f1b27..3e1432f 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -975,6 +975,10 @@ static int count_spte_number(struct pte_list_desc *desc) return first_free + desc_num * PTE_LIST_EXT; } +#define rcu_assign_pte_list(pte_list_p, value) \ + rcu_assign_pointer(*(unsigned long __rcu **)(pte_list_p), \ + (unsigned long *)(value)) + /* * Pte mapping structures: * @@ -994,7 +998,7 @@ static int pte_list_add(struct kvm_vcpu *vcpu, u64 *spte, if (!*pte_list) { rmap_printk("pte_list_add: %p %llx 0->1\n", spte, *spte); - *pte_list = (unsigned long)spte; + rcu_assign_pte_list(pte_list, spte); return 0; } @@ -1004,7 +1008,7 @@ static int pte_list_add(struct kvm_vcpu *vcpu, u64 *spte, desc->sptes[0] = (u64 *)*pte_list; desc->sptes[1] = spte; desc_mark_nulls(pte_list, desc); - *pte_list = (unsigned long)desc | 1; + rcu_assign_pte_list(pte_list, (unsigned long)desc | 1); return 1; } @@ -1017,7 +1021,7 @@ static int pte_list_add(struct kvm_vcpu *vcpu, u64 *spte, new_desc = mmu_alloc_pte_list_desc(vcpu); new_desc->more = desc; desc = new_desc; - *pte_list = (unsigned long)desc | 1; + rcu_assign_pte_list(pte_list, (unsigned long)desc | 1); } free_pos = find_first_free(desc); @@ -1125,6 +1129,51 @@ static void pte_list_walk(unsigned long *pte_list, pte_list_walk_fn fn) WARN_ON(desc_get_nulls_value(desc) != pte_list); } +/* The caller should hold rcu lock. */ +static void pte_list_walk_lockless(unsigned long *pte_list, + pte_list_walk_fn fn) +{ + struct pte_list_desc *desc; + unsigned long pte_list_value; + int i; + +restart: + /* + * Force the pte_list to be reloaded. + * + * See the comments in hlist_nulls_for_each_entry_rcu(). + */ + barrier(); + pte_list_value = *rcu_dereference(pte_list); + if (!pte_list_value) + return; + + if (!(pte_list_value & 1)) + return fn((u64 *)pte_list_value); + + desc = (struct pte_list_desc *)(pte_list_value & ~1ul); + while (!desc_is_a_nulls(desc)) { + /* + * We should do top-down walk since we always use the higher + * indices to replace the deleted entry if only one desc is + * used in the rmap when a spte is removed. Otherwise the + * moved entry will be missed. + */ + for (i = PTE_LIST_EXT - 1; i >= 0; i--) + if (desc->sptes[i]) + fn(desc->sptes[i]); + + desc = rcu_dereference(desc->more); + + /* It is being initialized. */ + if (unlikely(!desc)) + goto restart; + } + + if (unlikely(desc_get_nulls_value(desc) != pte_list)) + goto restart; +} + static unsigned long *__gfn_to_rmap(gfn_t gfn, int level, struct kvm_memory_slot *slot) { @@ -4651,7 +4700,7 @@ int kvm_mmu_module_init(void) { pte_list_desc_cache = kmem_cache_create("pte_list_desc", sizeof(struct pte_list_desc), - 0, 0, NULL); + 0, SLAB_DESTROY_BY_RCU, NULL); if (!pte_list_desc_cache) goto nomem; -- 1.8.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/