From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DC0C1C10F0E for ; Tue, 9 Apr 2019 08:07:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A41B320663 for ; Tue, 9 Apr 2019 08:07:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726585AbfDIIHY (ORCPT ); Tue, 9 Apr 2019 04:07:24 -0400 Received: from szxga04-in.huawei.com ([45.249.212.190]:5701 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726079AbfDIIHY (ORCPT ); Tue, 9 Apr 2019 04:07:24 -0400 Received: from DGGEMS402-HUB.china.huawei.com (unknown [172.30.72.59]) by Forcepoint Email with ESMTP id 570CAE799314B82CC4BF; Tue, 9 Apr 2019 16:07:21 +0800 (CST) Received: from [127.0.0.1] (10.184.12.158) by DGGEMS402-HUB.china.huawei.com (10.3.19.202) with Microsoft SMTP Server id 14.3.408.0; Tue, 9 Apr 2019 16:07:12 +0800 Subject: Re: [PATCH] kvm: arm: Skip stage2 huge mappings for unaligned ipa backed by THP To: Suzuki K Poulose , CC: , , , , , , , , References: <1554203176-3958-1-git-send-email-suzuki.poulose@arm.com> <2ea55b9c-09da-c3d0-3616-aa6be85b5a46@huawei.com> <44ffad26-a407-4603-0bb6-145f7290adbe@huawei.com> <730c25b4-dbc5-8d8b-514c-4ed8641701ce@arm.com> From: Zenghui Yu Message-ID: <1b398e29-e2d5-2a58-b4ca-c72979a170d8@huawei.com> Date: Tue, 9 Apr 2019 16:05:58 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:64.0) Gecko/20100101 Thunderbird/64.0 MIME-Version: 1.0 In-Reply-To: <730c25b4-dbc5-8d8b-514c-4ed8641701ce@arm.com> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.184.12.158] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2019/4/9 2:40, Suzuki K Poulose wrote: > Hi Zenhui, > > On 04/08/2019 04:11 PM, Zenghui Yu wrote: >> Hi Suzuki, >> >> Thanks for the reply. >> > > ... > >>>> Hi Suzuki, >>>> >>>> Why not making use of fault_supports_stage2_huge_mapping()?  Let it do >>>> some checks for us. >>>> >>>> fault_supports_stage2_huge_mapping() was intended to do a *two-step* >>>> check to tell us that can we create stage2 huge block mappings, and >>>> this >>>> check is both for hugetlbfs and THP.  With commit a80868f398554842b14, >>>> we pass PAGE_SIZE as "map_size" for normal size pages (which turned out >>>> to be almost meaningless), and unfortunately the THP check no longer >>>> works. >>> >>> Thats correct. >>> >>>> >>>> So we want to rework *THP* check process.  Your patch fixes the first >>>> checking-step, but the second is still missed, am I wrong? >>> >>> It fixes the step explicitly for the THP by making sure that the GPA and >>> the HVA are aligned to the map size. >> >> Yes, I understand how your patch had fixed the issue.  But what I'm >> really concerned about here is the *second* checking-step in >> fault_supports_stage2_huge_mapping(). >> >> We have to check if we are mapping a non-block aligned or non-block >> sized memslot, if so, we can not create block mappings for the beginning >> and end of this memslot.  This is what the second part of >> fault_supports_stage2_huge_mapping() had done. >> >> I haven't seen this checking-step in your patch, did I miss something? >> > > I see. > >>> I don't think this calls for a VM_BUG_ON(). It is simply a case where >>> the GPA is not aligned to HVA, but for normal VMA that could be made >>> THP. >>> >>> We had this VM_BUG_ON(), which would have never hit because we would >>> have set force_pte if they were not aligned. >> >> Yes, I agree. >> >>>>> +        /* Skip memslots with unaligned IPA and user address */ >>>>> +        if ((gfn & mask) != (pfn & mask)) >>>>> +            return false; >>>>>           if (pfn & mask) { >>>>>               *ipap &= PMD_MASK; >>>>>               kvm_release_pfn_clean(pfn); >>>>> >>>> >>>> ---8>--- >>>> >>>> Rework fault_supports_stage2_huge_mapping(), let it check THP again. >>>> >>>> Signed-off-by: Zenghui Yu >>>> --- >>>>   virt/kvm/arm/mmu.c | 11 ++++++++++- >>>>   1 file changed, 10 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c >>>> index 27c9583..5e1b258 100644 >>>> --- a/virt/kvm/arm/mmu.c >>>> +++ b/virt/kvm/arm/mmu.c >>>> @@ -1632,6 +1632,15 @@ static bool >>>> fault_supports_stage2_huge_mapping(struct kvm_memory_slot *memslot, >>>>       uaddr_end = uaddr_start + size; >>>> >>>>       /* >>>> +     * If the memslot is _not_ backed by hugetlbfs, then check if it >>>> +     * can be backed by transparent hugepages. >>>> +     * >>>> +     * Currently only PMD_SIZE THPs are supported, revisit it later. >>>> +     */ >>>> +    if (map_size == PAGE_SIZE) >>>> +        map_size = PMD_SIZE; >>>> + >>> >>> This looks hackish. What is we support PUD_SIZE huge page in the future >>> ? >> >> Yes, this might make the code a little difficult to understand. But by >> doing so, we follow the same logic before commit a80868f398554842b14, >> that said, we do the two-step checking for normal size pages in >> fault_supports_stage2_huge_mapping(), to decide if we can create THP >> mappings for these pages. >> >> As for PUD_SIZE THPs, to be honest, I have no idea now :( > > How about the following diff ? > > diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c > index 97b5417..98e5cec 100644 > --- a/virt/kvm/arm/mmu.c > +++ b/virt/kvm/arm/mmu.c > @@ -1791,7 +1791,8 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, > phys_addr_t fault_ipa, >           * currently supported. This code will need to be >           * updated to support other THP sizes. >           */ > -        if (transparent_hugepage_adjust(&pfn, &fault_ipa)) > +        if (fault_supports_stage2_huge_mappings(memslot, hva, PMD_SIZE) && > +            transparent_hugepage_adjust(&pfn, &fault_ipa)) >              vma_pagesize = PMD_SIZE; >      } I think this is good enough for the issue. (One minor concern: With this change, it seems that we no longer need "force_pte" and can just use "logging_active" instead. But this is not much related to what we're fixing.) thanks.