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 39746C10F0E for ; Tue, 9 Apr 2019 14:57:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 01E7920674 for ; Tue, 9 Apr 2019 14:57:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726578AbfDIO5D (ORCPT ); Tue, 9 Apr 2019 10:57:03 -0400 Received: from foss.arm.com ([217.140.101.70]:39432 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726112AbfDIO5D (ORCPT ); Tue, 9 Apr 2019 10:57:03 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id C7EB415AB; Tue, 9 Apr 2019 07:57:02 -0700 (PDT) Received: from [10.37.12.144] (unknown [10.37.12.144]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 4ACF63F68F; Tue, 9 Apr 2019 07:57:00 -0700 (PDT) Subject: Re: [PATCH] kvm: arm: Skip stage2 huge mappings for unaligned ipa backed by THP To: yuzenghui@huawei.com, linux-arm-kernel@lists.infradead.org Cc: kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, eric.auger@redhat.com, marc.zyngier@arm.com, christoffer.dall@arm.com, zhengxiang9@huawei.com, andrew.murray@arm.com, wanghaibin.wang@huawei.com 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> <1b398e29-e2d5-2a58-b4ca-c72979a170d8@huawei.com> From: Suzuki K Poulose Message-ID: <520e277c-f096-a84b-8405-636b19e4cc46@arm.com> Date: Tue, 9 Apr 2019 15:59:16 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <1b398e29-e2d5-2a58-b4ca-c72979a170d8@huawei.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Zenghui On 04/09/2019 09:05 AM, Zenghui Yu wrote: > > > 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.) I would still leave the force_pte there to avoid checking for a THP case in a situation where we forced to PTE level mapping on a hugepage backed VMA. It would serve to avoid another check. Cheers Suzuki > > > thanks. > >