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=-15.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,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 5EB8BC433DB for ; Thu, 14 Jan 2021 09:29:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2BBED23359 for ; Thu, 14 Jan 2021 09:29:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728344AbhANJ26 (ORCPT ); Thu, 14 Jan 2021 04:28:58 -0500 Received: from szxga01-in.huawei.com ([45.249.212.187]:4136 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728076AbhANJ24 (ORCPT ); Thu, 14 Jan 2021 04:28:56 -0500 Received: from dggeme763-chm.china.huawei.com (unknown [172.30.72.53]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4DGf8y6R29zXyj9; Thu, 14 Jan 2021 17:27:14 +0800 (CST) Received: from [10.174.187.128] (10.174.187.128) by dggeme763-chm.china.huawei.com (10.3.19.109) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.2106.2; Thu, 14 Jan 2021 17:28:09 +0800 Subject: Re: [PATCH v2 2/3] KVM: arm64: Add prejudgement for relaxing permissions only case in stage2 translation fault handler To: Will Deacon CC: , , Marc Zyngier , Catalin Marinas , James Morse , Julien Thierry , Suzuki K Poulose , Gavin Shan , Quentin Perret , , , , References: <20201216122844.25092-1-wangyanan55@huawei.com> <20201216122844.25092-3-wangyanan55@huawei.com> <20210113154414.GA11892@willie-the-truck> From: "wangyanan (Y)" Message-ID: Date: Thu, 14 Jan 2021 17:28:09 +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: <20210113154414.GA11892@willie-the-truck> 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 dggeme763-chm.china.huawei.com (10.3.19.109) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021/1/13 23:44, Will Deacon wrote: > On Wed, Dec 16, 2020 at 08:28:43PM +0800, Yanan Wang wrote: >> In dirty-logging, or dirty-logging-stopped time, even normal running >> time of a guest configed with huge mappings and numbers of vCPUs, >> translation faults by different vCPUs on the same GPA could occur >> successively almost at the same time. There are two reasons for it. >> >> (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. >> >> 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. >> >> Signed-off-by: Yanan Wang >> --- >> arch/arm64/kvm/hyp/pgtable.c | 28 +++++++++++++++++++--------- >> 1 file changed, 19 insertions(+), 9 deletions(-) >> >> diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c >> index 350f9f810930..8225ced49bad 100644 >> --- a/arch/arm64/kvm/hyp/pgtable.c >> +++ b/arch/arm64/kvm/hyp/pgtable.c >> @@ -45,6 +45,10 @@ >> >> #define KVM_PTE_LEAF_ATTR_HI_S2_XN BIT(54) >> >> +#define KVM_PTE_LEAF_ATTR_S2_PERMS (KVM_PTE_LEAF_ATTR_LO_S2_S2AP_R | \ >> + KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W | \ >> + KVM_PTE_LEAF_ATTR_HI_S2_XN) >> + >> struct kvm_pgtable_walk_data { >> struct kvm_pgtable *pgt; >> struct kvm_pgtable_walker *walker; >> @@ -460,7 +464,7 @@ static int stage2_map_set_prot_attr(enum kvm_pgtable_prot prot, >> return 0; >> } >> >> -static bool stage2_map_walker_try_leaf(u64 addr, u64 end, u32 level, >> +static int stage2_map_walker_try_leaf(u64 addr, u64 end, u32 level, >> kvm_pte_t *ptep, >> struct stage2_map_data *data) >> { >> @@ -469,13 +473,18 @@ static bool stage2_map_walker_try_leaf(u64 addr, u64 end, u32 level, >> struct page *page = virt_to_page(ptep); >> >> if (!kvm_block_mapping_supported(addr, end, phys, level)) >> - return false; >> + return 1; > It would probably be cleaner to return another error code here, as we > have failed to install a mapping (e.g. E2BIG or perhaps more perversely, > ENOTBLK). Then the caller can decide to install a trable. > Ok, I will make some adjustment for this and post the v3 soon after. Thanks, Yanan.