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=-11.1 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 21A5CC433E9 for ; Mon, 28 Dec 2020 02:47:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F119720796 for ; Mon, 28 Dec 2020 02:47:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726396AbgL1CrG (ORCPT ); Sun, 27 Dec 2020 21:47:06 -0500 Received: from szxga01-in.huawei.com ([45.249.212.187]:4124 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726286AbgL1CrG (ORCPT ); Sun, 27 Dec 2020 21:47:06 -0500 Received: from dggeme752-chm.china.huawei.com (unknown [172.30.72.57]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4D423S3XW4zXsl4; Mon, 28 Dec 2020 10:45:40 +0800 (CST) Received: from [10.174.187.128] (10.174.187.128) by dggeme752-chm.china.huawei.com (10.3.19.98) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.1913.5; Mon, 28 Dec 2020 10:46:22 +0800 Subject: Re: [PATCH v2 0/3] RFC: Solve several problems in stage 2 translation To: , , Marc Zyngier , Catalin Marinas , Will Deacon , James Morse , Julien Thierry , Suzuki K Poulose , Gavin Shan , Quentin Perret CC: , , , References: <20201216122844.25092-1-wangyanan55@huawei.com> From: "wangyanan (Y)" Message-ID: Date: Mon, 28 Dec 2020 10:46:21 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0 MIME-Version: 1.0 In-Reply-To: <20201216122844.25092-1-wangyanan55@huawei.com> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US X-Originating-IP: [10.174.187.128] X-ClientProxiedBy: dggeme702-chm.china.huawei.com (10.1.199.98) To dggeme752-chm.china.huawei.com (10.3.19.98) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Will, Marc, Gently Ping. Is there any comments about this V2 series? Many thanks, Yanan. On 2020/12/16 20:28, Yanan Wang wrote: > Hi, this is the second version, thanks for reading. > > PATCH1/3: > Procedures of hyp stage 1 mapping and guest stage 2 mapping are different, but > they are tied closely by function kvm_set_valid_leaf_pte(). So separate them by > rewriting kvm_set_valid_leaf_pte(). > > PATCH2/3: > To avoid unnecessary update and small loops, add prejudgement in the translation > fault handler: Skip updating the PTE with break-before-make if we are trying to > recreate the exact same mapping or only change the access permissions. Actually, > change of permissions will be handled through the relax_perms path next time if > necessary. > > (1) If there are some vCPUs accessing the same GPA at the same time and the leaf > PTE is not set yet, then they will all cause translation faults and the first vCPU > holding mmu_lock will set valid leaf PTE, and the others will later update the old > PTE with a new one if they are different. > > (2) When changing a leaf entry or a table entry with break-before-make, if there > are some vCPUs accessing the same GPA just catch the moment when the target PTE > is set invalid in a BBM procedure coincidentally, they will all cause translation > faults and will later update the old PTE with a new one if they are different. > > The worst case can be like this: vCPU A causes a translation fault with RW prot and > sets the leaf PTE with RW permissions, and then the next vCPU B with RO prot updates > the PTE back to RO permissions with break-before-make. And the BBM-invalid moment > may trigger more unnecessary translation faults, then some useless small loops might > occur which could lead to vCPU stuck. > > PATCH3/3: > We now mark the page dirty and set the bitmap before calling fault handlers in > user_mem_abort(), and we might end up having spurious dirty pages if update of > permissions or mapping has failed. So, mark the page dirty only if the fault is > handled successfully. > > Let the guest directly enter again but not return to userspace if we were trying > to recreate the same mapping or only change access permissions with BBM, which is > not permitted in the mapping path. > > Changes from v1: > - Make part of the diff as an independent patch (PATCH1/3), > and add Will's Signed-off-by. > - Use *return -EPERM* way when changing permissions only in the mapping path. > - Add a new patch (PATCH3/3). > > Yanan Wang (3): > KVM: arm64: Decouple partial code of hyp stage 1 mapping and guest > stage 2 mapping > KVM: arm64: Add prejudgement for relaxing permissions only case in > stage2 translation fault handler > KVM: arm64: Mark the page dirty only if the fault is handled > successfully > > arch/arm64/kvm/hyp/pgtable.c | 78 ++++++++++++++++++++---------------- > arch/arm64/kvm/mmu.c | 18 +++++++-- > 2 files changed, 58 insertions(+), 38 deletions(-) >