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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 B4B22C43460 for ; Fri, 23 Apr 2021 01:06:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 83DD9613A9 for ; Fri, 23 Apr 2021 01:06:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236592AbhDWBHK (ORCPT ); Thu, 22 Apr 2021 21:07:10 -0400 Received: from szxga06-in.huawei.com ([45.249.212.32]:17392 "EHLO szxga06-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230367AbhDWBHJ (ORCPT ); Thu, 22 Apr 2021 21:07:09 -0400 Received: from DGGEMS407-HUB.china.huawei.com (unknown [172.30.72.60]) by szxga06-in.huawei.com (SkyGuard) with ESMTP id 4FRGKF14mpzlZ7r; Fri, 23 Apr 2021 09:04:33 +0800 (CST) Received: from [10.174.187.224] (10.174.187.224) by DGGEMS407-HUB.china.huawei.com (10.3.19.207) with Microsoft SMTP Server id 14.3.498.0; Fri, 23 Apr 2021 09:06:21 +0800 Subject: Re: [PATCH] KVM: arm64: Correctly handle the mmio faulting To: Santosh Shukla , "Tarun Gupta (SW-GPU)" References: <1603297010-18787-1-git-send-email-sashukla@nvidia.com> <8b20dfc0-3b5e-c658-c47d-ebc50d20568d@huawei.com> <2e23aaa7-0c8d-13ba-2eae-9e6ab2adc587@redhat.com> <871rb3rgpl.wl-maz@kernel.org> <87v98eq0dh.wl-maz@kernel.org> CC: Marc Zyngier , Gavin Shan , , , , , , "Wanghaibin (D)" From: Keqian Zhu Message-ID: Date: Fri, 23 Apr 2021 09:06:20 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.7.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.187.224] X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021/4/22 16:00, Santosh Shukla wrote: > On Thu, Apr 22, 2021 at 1:07 PM Tarun Gupta (SW-GPU) > wrote: >> >> >> >> On 4/22/2021 12:20 PM, Marc Zyngier wrote: >>> External email: Use caution opening links or attachments >>> >>> >>> On Thu, 22 Apr 2021 03:02:00 +0100, >>> Gavin Shan wrote: >>>> >>>> Hi Marc, >>>> >>>> On 4/21/21 9:59 PM, Marc Zyngier wrote: >>>>> On Wed, 21 Apr 2021 07:17:44 +0100, >>>>> Keqian Zhu wrote: >>>>>> On 2021/4/21 14:20, Gavin Shan wrote: >>>>>>> On 4/21/21 12:59 PM, Keqian Zhu wrote: >>>>>>>> On 2020/10/22 0:16, Santosh Shukla wrote: >>>>>>>>> The Commit:6d674e28 introduces a notion to detect and handle the >>>>>>>>> device mapping. The commit checks for the VM_PFNMAP flag is set >>>>>>>>> in vma->flags and if set then marks force_pte to true such that >>>>>>>>> if force_pte is true then ignore the THP function check >>>>>>>>> (/transparent_hugepage_adjust()). >>>>>>>>> >>>>>>>>> There could be an issue with the VM_PFNMAP flag setting and checking. >>>>>>>>> For example consider a case where the mdev vendor driver register's >>>>>>>>> the vma_fault handler named vma_mmio_fault(), which maps the >>>>>>>>> host MMIO region in-turn calls remap_pfn_range() and maps >>>>>>>>> the MMIO's vma space. Where, remap_pfn_range implicitly sets >>>>>>>>> the VM_PFNMAP flag into vma->flags. >>>>>>>> Could you give the name of the mdev vendor driver that triggers this issue? >>>>>>>> I failed to find one according to your description. Thanks. >>>>>>>> >>>>>>> >>>>>>> I think it would be fixed in driver side to set VM_PFNMAP in >>>>>>> its mmap() callback (call_mmap()), like vfio PCI driver does. >>>>>>> It means it won't be delayed until page fault is issued and >>>>>>> remap_pfn_range() is called. It's determined from the beginning >>>>>>> that the vma associated the mdev vendor driver is serving as >>>>>>> PFN remapping purpose. So the vma should be populated completely, >>>>>>> including the VM_PFNMAP flag before it becomes visible to user >>>>>>> space. >>>>> >>>>> Why should that be a requirement? Lazy populating of the VMA should be >>>>> perfectly acceptable if the fault can only happen on the CPU side. >>>>> > > Right. > Hi keqian, > You can refer to case > http://lkml.iu.edu/hypermail/linux/kernel/2010.3/00952.html Hi Santosh, Yeah, thanks for that. BRs, Keqian