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 3DF64C10F13 for ; Mon, 8 Apr 2019 18:37:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1DCEA206C0 for ; Mon, 8 Apr 2019 18:37:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729122AbfDHShz (ORCPT ); Mon, 8 Apr 2019 14:37:55 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:54422 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727258AbfDHShz (ORCPT ); Mon, 8 Apr 2019 14:37:55 -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 7804E15BE; Mon, 8 Apr 2019 11:37:54 -0700 (PDT) Received: from [10.37.12.66] (unknown [10.37.12.66]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 1342F3F718; Mon, 8 Apr 2019 11:37:51 -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> From: Suzuki K Poulose Message-ID: <730c25b4-dbc5-8d8b-514c-4ed8641701ce@arm.com> Date: Mon, 8 Apr 2019 19:40:09 +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: <44ffad26-a407-4603-0bb6-145f7290adbe@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 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; } -- 2.7.4 Suzuki