Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758621Ab3EWLOL (ORCPT ); Thu, 23 May 2013 07:14:11 -0400 Received: from e28smtp06.in.ibm.com ([122.248.162.6]:36474 "EHLO e28smtp06.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758522Ab3EWLOJ (ORCPT ); Thu, 23 May 2013 07:14:09 -0400 Message-ID: <519DF9F6.1060902@linux.vnet.ibm.com> Date: Thu, 23 May 2013 19:13:58 +0800 From: Xiao Guangrong User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130110 Thunderbird/17.0.2 MIME-Version: 1.0 To: Gleb Natapov CC: avi.kivity@gmail.com, mtosatti@redhat.com, pbonzini@redhat.com, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH v7 09/11] KVM: MMU: introduce kvm_mmu_prepare_zap_obsolete_page References: <1369252560-11611-1-git-send-email-xiaoguangrong@linux.vnet.ibm.com> <1369252560-11611-10-git-send-email-xiaoguangrong@linux.vnet.ibm.com> <20130523055725.GA26157@redhat.com> <519DB372.3080803@linux.vnet.ibm.com> <20130523061818.GC26157@redhat.com> <519DB7D3.7030101@linux.vnet.ibm.com> <20130523073708.GE26157@redhat.com> <519DCA38.30200@linux.vnet.ibm.com> <20130523080922.GG26157@redhat.com> In-Reply-To: <20130523080922.GG26157@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13052311-9574-0000-0000-000007FE0FB7 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6676 Lines: 176 On 05/23/2013 04:09 PM, Gleb Natapov wrote: > On Thu, May 23, 2013 at 03:50:16PM +0800, Xiao Guangrong wrote: >> On 05/23/2013 03:37 PM, Gleb Natapov wrote: >>> On Thu, May 23, 2013 at 02:31:47PM +0800, Xiao Guangrong wrote: >>>> On 05/23/2013 02:18 PM, Gleb Natapov wrote: >>>>> On Thu, May 23, 2013 at 02:13:06PM +0800, Xiao Guangrong wrote: >>>>>> On 05/23/2013 01:57 PM, Gleb Natapov wrote: >>>>>>> On Thu, May 23, 2013 at 03:55:58AM +0800, Xiao Guangrong wrote: >>>>>>>> It is only used to zap the obsolete page. Since the obsolete page >>>>>>>> will not be used, we need not spend time to find its unsync children >>>>>>>> out. Also, we delete the page from shadow page cache so that the page >>>>>>>> is completely isolated after call this function. >>>>>>>> >>>>>>>> The later patch will use it to collapse tlb flushes >>>>>>>> >>>>>>>> Signed-off-by: Xiao Guangrong >>>>>>>> --- >>>>>>>> arch/x86/kvm/mmu.c | 46 +++++++++++++++++++++++++++++++++++++++++----- >>>>>>>> 1 files changed, 41 insertions(+), 5 deletions(-) >>>>>>>> >>>>>>>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c >>>>>>>> index 9b57faa..e676356 100644 >>>>>>>> --- a/arch/x86/kvm/mmu.c >>>>>>>> +++ b/arch/x86/kvm/mmu.c >>>>>>>> @@ -1466,7 +1466,7 @@ static inline void kvm_mod_used_mmu_pages(struct kvm *kvm, int nr) >>>>>>>> static void kvm_mmu_free_page(struct kvm_mmu_page *sp) >>>>>>>> { >>>>>>>> ASSERT(is_empty_shadow_page(sp->spt)); >>>>>>>> - hlist_del(&sp->hash_link); >>>>>>>> + hlist_del_init(&sp->hash_link); >>>>>>> Why do you need hlist_del_init() here? Why not move it into >>>>>> >>>>>> Since the hlist will be double freed. We will it like this: >>>>>> >>>>>> kvm_mmu_prepare_zap_obsolete_page(page, list); >>>>>> kvm_mmu_commit_zap_page(list); >>>>>> kvm_mmu_free_page(page); >>>>>> >>>>>> The first place is kvm_mmu_prepare_zap_obsolete_page(page), which have >>>>>> deleted the hash list. >>>>>> >>>>>>> kvm_mmu_prepare_zap_page() like we discussed it here: >>>>>>> https://patchwork.kernel.org/patch/2580351/ instead of doing >>>>>>> it differently for obsolete and non obsolete pages? >>>>>> >>>>>> It is can break the hash-list walking: we should rescan the >>>>>> hash list once the page is prepared-ly zapped. >>>>>> >>>>>> I mentioned it in the changelog: >>>>>> >>>>>> 4): drop the patch which deleted page from hash list at the "prepare" >>>>>> time since it can break the walk based on hash list. >>>>> Can you elaborate on how this can happen? >>>> >>>> There is a example: >>>> >>>> int kvm_mmu_unprotect_page(struct kvm *kvm, gfn_t gfn) >>>> { >>>> struct kvm_mmu_page *sp; >>>> LIST_HEAD(invalid_list); >>>> int r; >>>> >>>> pgprintk("%s: looking for gfn %llx\n", __func__, gfn); >>>> r = 0; >>>> spin_lock(&kvm->mmu_lock); >>>> for_each_gfn_indirect_valid_sp(kvm, sp, gfn) { >>>> pgprintk("%s: gfn %llx role %x\n", __func__, gfn, >>>> sp->role.word); >>>> r = 1; >>>> kvm_mmu_prepare_zap_page(kvm, sp, &invalid_list); >>>> } >>>> kvm_mmu_commit_zap_page(kvm, &invalid_list); >>>> spin_unlock(&kvm->mmu_lock); >>>> >>>> return r; >>>> } >>>> >>>> It works fine since kvm_mmu_prepare_zap_page does not touch the hash list. >>>> If we delete hlist in kvm_mmu_prepare_zap_page(), this kind of codes should >>>> be changed to: >>>> >>>> restart: >>>> for_each_gfn_indirect_valid_sp(kvm, sp, gfn) { >>>> pgprintk("%s: gfn %llx role %x\n", __func__, gfn, >>>> sp->role.word); >>>> r = 1; >>>> if (kvm_mmu_prepare_zap_page(kvm, sp, &invalid_list)) >>>> goto restart; >>>> } >>>> kvm_mmu_commit_zap_page(kvm, &invalid_list); >>>> >>> Hmm, yes. So lets leave it as is and always commit invalid_list before >> >> So, you mean drop this patch and the patch of >> KVM: MMU: collapse TLB flushes when zap all pages? >> > We still want to add kvm_reload_remote_mmus() to > kvm_mmu_invalidate_zap_all_pages(). But yes, we disable a nice > optimization here. So may be skipping obsolete pages while walking > hashtable is better solution. I am willing to use this way instead, but it looks worse than this patch: diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index 9b57faa..810410c 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -1466,7 +1466,7 @@ static inline void kvm_mod_used_mmu_pages(struct kvm *kvm, int nr) static void kvm_mmu_free_page(struct kvm_mmu_page *sp) { ASSERT(is_empty_shadow_page(sp->spt)); - hlist_del(&sp->hash_link); + hlist_del_init(&sp->hash_link); list_del(&sp->link); free_page((unsigned long)sp->spt); if (!sp->role.direct) @@ -1648,14 +1648,20 @@ static int kvm_mmu_prepare_zap_page(struct kvm *kvm, struct kvm_mmu_page *sp, static void kvm_mmu_commit_zap_page(struct kvm *kvm, struct list_head *invalid_list); +static bool is_obsolete_sp(struct kvm *kvm, struct kvm_mmu_page *sp) +{ + return unlikely(sp->mmu_valid_gen != kvm->arch.mmu_valid_gen); +} + #define for_each_gfn_sp(_kvm, _sp, _gfn) \ hlist_for_each_entry(_sp, \ &(_kvm)->arch.mmu_page_hash[kvm_page_table_hashfn(_gfn)], hash_link) \ - if ((_sp)->gfn != (_gfn)) {} else + if ((_sp)->gfn != (_gfn) || is_obsolete_sp(_kvm, _sp)) {} else #define for_each_gfn_indirect_valid_sp(_kvm, _sp, _gfn) \ for_each_gfn_sp(_kvm, _sp, _gfn) \ - if ((_sp)->role.direct || (_sp)->role.invalid) {} else + if ((_sp)->role.direct || \ + (_sp)->role.invalid || is_obsolete_sp(_kvm, _sp)) {} else /* @sp->gfn should be write-protected at the call site */ static int __kvm_sync_page(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp, @@ -1838,11 +1844,6 @@ static void clear_sp_write_flooding_count(u64 *spte) __clear_sp_write_flooding_count(sp); } -static bool is_obsolete_sp(struct kvm *kvm, struct kvm_mmu_page *sp) -{ - return unlikely(sp->mmu_valid_gen != kvm->arch.mmu_valid_gen); -} - static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu, gfn_t gfn, gva_t gaddr, @@ -2085,11 +2086,15 @@ static int kvm_mmu_prepare_zap_page(struct kvm *kvm, struct kvm_mmu_page *sp, if (sp->unsync) kvm_unlink_unsync_page(kvm, sp); + if (!sp->root_count) { /* Count self */ ret++; list_move(&sp->link, invalid_list); kvm_mod_used_mmu_pages(kvm, -1); + + if (unlikely(is_obsolete_sp(kvm, sp))) + hlist_del_init(&sp->hash_link); } else { list_move(&sp->link, &kvm->arch.active_mmu_pages); kvm_reload_remote_mmus(kvm); isn't it? -- 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/