Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751681Ab3CRMaD (ORCPT ); Mon, 18 Mar 2013 08:30:03 -0400 Received: from e28smtp03.in.ibm.com ([122.248.162.3]:54840 "EHLO e28smtp03.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751081Ab3CRMaA (ORCPT ); Mon, 18 Mar 2013 08:30:00 -0400 Message-ID: <514708A9.8040009@linux.vnet.ibm.com> Date: Mon, 18 Mar 2013 20:29:29 +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: Marcelo Tosatti , LKML , KVM Subject: Re: [PATCH 5/5] KVM: MMU: fast invalid all mmio sptes References: <51433D98.4050605@linux.vnet.ibm.com> <51433E71.2070107@linux.vnet.ibm.com> <20130317150239.GM11223@redhat.com> <5146CB92.7060203@linux.vnet.ibm.com> <20130318091303.GA1276@redhat.com> In-Reply-To: <20130318091303.GA1276@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: 13031812-3864-0000-0000-00000750CB94 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6968 Lines: 173 On 03/18/2013 05:13 PM, Gleb Natapov wrote: > On Mon, Mar 18, 2013 at 04:08:50PM +0800, Xiao Guangrong wrote: >> On 03/17/2013 11:02 PM, Gleb Natapov wrote: >>> On Fri, Mar 15, 2013 at 11:29:53PM +0800, Xiao Guangrong wrote: >>>> This patch tries to introduce a very simple and scale way to invalid all >>>> mmio sptes - it need not walk any shadow pages and hold mmu-lock >>>> >>>> KVM maintains a global mmio invalid generation-number which is stored in >>>> kvm->arch.mmio_invalid_gen and every mmio spte stores the current global >>>> generation-number into his available bits when it is created >>>> >>>> When KVM need zap all mmio sptes, it just simply increase the global >>>> generation-number. When guests do mmio access, KVM intercepts a MMIO #PF >>>> then it walks the shadow page table and get the mmio spte. If the >>>> generation-number on the spte does not equal the global generation-number, >>>> it will go to the normal #PF handler to update the mmio spte >>>> >>>> Since 19 bits are used to store generation-number on mmio spte, the >>>> generation-number can be round after 33554432 times. It is large enough >>>> for nearly all most cases, but making the code be more strong, we zap all >>>> shadow pages when the number is round >>>> >>> Very nice idea, but why drop Takuya patches instead of using >>> kvm_mmu_zap_mmio_sptes() when generation number overflows. >> >> I am not sure whether it is still needed. Requesting to zap all mmio sptes for >> more than 500000 times is really really rare, it nearly does not happen. >> (By the way, 33554432 is wrong in the changelog, i just copy that for my origin >> implantation.) And, after my patch optimizing zapping all shadow pages, >> zap-all-sps should not be a problem anymore since it does not take too much lock >> time. >> >> Your idea? >> > I expect 500000 to become less since I already had plans to store some Interesting, just curious, what are the plans? ;) > information in mmio spte. Even if all zap-all-sptes becomes faster we > still needlessly zap all sptes while we can zap only mmio. Okay. > >>> >>> >>>> Signed-off-by: Xiao Guangrong >>>> --- >>>> arch/x86/include/asm/kvm_host.h | 2 + >>>> arch/x86/kvm/mmu.c | 61 +++++++++++++++++++++++++++++++++------ >>>> arch/x86/kvm/mmutrace.h | 17 +++++++++++ >>>> arch/x86/kvm/paging_tmpl.h | 7 +++- >>>> arch/x86/kvm/vmx.c | 4 ++ >>>> arch/x86/kvm/x86.c | 6 +-- >>>> 6 files changed, 82 insertions(+), 15 deletions(-) >>>> >>>> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h >>>> index ef7f4a5..572398e 100644 >>>> --- a/arch/x86/include/asm/kvm_host.h >>>> +++ b/arch/x86/include/asm/kvm_host.h >>>> @@ -529,6 +529,7 @@ struct kvm_arch { >>>> unsigned int n_requested_mmu_pages; >>>> unsigned int n_max_mmu_pages; >>>> unsigned int indirect_shadow_pages; >>>> + unsigned int mmio_invalid_gen; >>> Why invalid? Should be mmio_valid_gen or mmio_current_get. >> >> mmio_invalid_gen is only updated in kvm_mmu_invalidate_mmio_sptes, >> so i named it as _invalid_. But mmio_valid_gen is good for me. >> > It holds currently valid value though, so calling it "invalid" is > confusing. I agree. > >>> >>>> struct hlist_head mmu_page_hash[KVM_NUM_MMU_PAGES]; >>>> /* >>>> * Hash table of struct kvm_mmu_page. >>>> @@ -765,6 +766,7 @@ void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot); >>>> void kvm_mmu_write_protect_pt_masked(struct kvm *kvm, >>>> struct kvm_memory_slot *slot, >>>> gfn_t gfn_offset, unsigned long mask); >>>> +void kvm_mmu_invalid_mmio_spte(struct kvm *kvm); >>> Agree with Takuya that kvm_mmu_invalidate_mmio_sptes() is a better name. >> >> Me too. >> >>> >>>> void kvm_mmu_zap_all(struct kvm *kvm); >>>> unsigned int kvm_mmu_calculate_mmu_pages(struct kvm *kvm); >>>> void kvm_mmu_change_mmu_pages(struct kvm *kvm, unsigned int kvm_nr_mmu_pages); >>>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c >>>> index 13626f4..7093a92 100644 >>>> --- a/arch/x86/kvm/mmu.c >>>> +++ b/arch/x86/kvm/mmu.c >>>> @@ -234,12 +234,13 @@ static unsigned int get_mmio_spte_generation(u64 spte) >>>> static void mark_mmio_spte(struct kvm *kvm, u64 *sptep, u64 gfn, >>>> unsigned access) >>>> { >>>> - u64 mask = generation_mmio_spte_mask(0); >>>> + unsigned int gen = ACCESS_ONCE(kvm->arch.mmio_invalid_gen); >>>> + u64 mask = generation_mmio_spte_mask(gen); >>>> >>>> access &= ACC_WRITE_MASK | ACC_USER_MASK; >>>> mask |= shadow_mmio_mask | access | gfn << PAGE_SHIFT; >>>> >>>> - trace_mark_mmio_spte(sptep, gfn, access, 0); >>>> + trace_mark_mmio_spte(sptep, gfn, access, gen); >>>> mmu_spte_set(sptep, mask); >>>> } >>>> >>>> @@ -269,6 +270,34 @@ static bool set_mmio_spte(struct kvm *kvm, u64 *sptep, gfn_t gfn, >>>> return false; >>>> } >>>> >>>> +static bool check_mmio_spte(struct kvm *kvm, u64 spte) >>>> +{ >>>> + return get_mmio_spte_generation(spte) == >>>> + ACCESS_ONCE(kvm->arch.mmio_invalid_gen); >>>> +} >>>> + >>>> +/* >>>> + * The caller should protect concurrent access on >>>> + * kvm->arch.mmio_invalid_gen. Currently, it is used by >>>> + * kvm_arch_commit_memory_region and protected by kvm->slots_lock. >>>> + */ >>>> +void kvm_mmu_invalid_mmio_spte(struct kvm *kvm) >>>> +{ >>>> + /* Ensure update memslot has been completed. */ >>>> + smp_mb(); >>> What barrier this one is paired with? >> >> It is paired with nothing. :) >> >> I used mb here just for avoid increasing the generation-number before updating >> the memslot. But on other sides (storing gen and checking gen), we do not need >> to care it - the worse case is that we emulate a memory-accessed instruction. >> > Are you warring that compiler can reorder instructions and put > instruction that increase generation number before updating memslot? > If yes then you need to use barrier() here. Or are you warring that > update may be seen in different order by another cpu? Then you need to > put another barring in the code that access memslot/generation number > and cares about the order. After more thinking, maybe i missed something. The correct order should be: The write side: update kvm->memslots smp_wmb() kvm->mmio_invalid_gen++ The read side: read kvm->mmio_invalid_gen++ smp_rmb(); search gfn in memslots (read all memslots) Otherwise, mmio spte would cache a newest generation-number and obsolete memslot info. But we read memslots out of mmu-lock on page fault path, we should pass mmio_invalid_gen to the page fault hander. In order to simplify the code, let's save the generation-number into kvm_memslots, then they can protected by SRCU. How about this? -- 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/