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,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=unavailable 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 611C0C433DB for ; Thu, 14 Jan 2021 12:12:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1120A23A55 for ; Thu, 14 Jan 2021 12:12:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726749AbhANMMD (ORCPT ); Thu, 14 Jan 2021 07:12:03 -0500 Received: from szxga05-in.huawei.com ([45.249.212.191]:11099 "EHLO szxga05-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726427AbhANMMD (ORCPT ); Thu, 14 Jan 2021 07:12:03 -0500 Received: from DGGEMS404-HUB.china.huawei.com (unknown [172.30.72.59]) by szxga05-in.huawei.com (SkyGuard) with ESMTP id 4DGjmm3wbLzMKPF; Thu, 14 Jan 2021 20:10:00 +0800 (CST) Received: from [10.174.184.42] (10.174.184.42) by DGGEMS404-HUB.china.huawei.com (10.3.19.204) with Microsoft SMTP Server id 14.3.498.0; Thu, 14 Jan 2021 20:11:09 +0800 Subject: Re: [PATCH 4/5] vfio/iommu_type1: Carefully use unmap_unpin_all during dirty tracking To: Alex Williamson References: <20210107092901.19712-1-zhukeqian1@huawei.com> <20210107092901.19712-5-zhukeqian1@huawei.com> <20210111144913.3092b1b1@omen.home.shazbot.org> <198f0afd-343a-9fbc-9556-95670ca76a2c@huawei.com> <20210112125331.789f47a5@omen.home.shazbot.org> CC: , , , , , Kirti Wankhede , Cornelia Huck , Will Deacon , "Marc Zyngier" , Catalin Marinas , "Mark Rutland" , James Morse , "Robin Murphy" , Joerg Roedel , Daniel Lezcano , Thomas Gleixner , "Suzuki K Poulose" , Julien Thierry , Andrew Morton , Alexios Zavras , , From: Keqian Zhu Message-ID: <14ee2346-ea9e-ab24-40d7-45a3bd16510d@huawei.com> Date: Thu, 14 Jan 2021 20:11:00 +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: <20210112125331.789f47a5@omen.home.shazbot.org> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.184.42] X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 2021/1/13 3:53, Alex Williamson wrote: > On Tue, 12 Jan 2021 20:04:38 +0800 > Keqian Zhu wrote: > >> On 2021/1/12 5:49, Alex Williamson wrote: >>> On Thu, 7 Jan 2021 17:29:00 +0800 >>> Keqian Zhu wrote: >>> >>>> If we detach group during dirty page tracking, we shouldn't remove >>>> vfio_dma, because dirty log will lose. >>>> >>>> But we don't prevent unmap_unpin_all in vfio_iommu_release, because >>>> under normal procedure, dirty tracking has been stopped. >>> >>> This looks like it's creating a larger problem than it's fixing, it's >>> not our job to maintain the dirty bitmap regardless of what the user >>> does. If the user detaches the last group in a container causing the >>> mappings within that container to be deconstructed before the user has >>> collected dirty pages, that sounds like a user error. A container with >>> no groups is de-privileged and therefore loses all state. Thanks, >>> >>> Alex >> >> Hi Alex, >> >> This looks good to me ;-). That's a reasonable constraint for user behavior. >> >> What about replacing this patch with an addition to the uapi document of >> VFIO_GROUP_UNSET_CONTAINER? User should pay attention to this when call this >> ioctl during dirty tracking. > > Here's the current uapi comment: > > /** > * VFIO_GROUP_UNSET_CONTAINER - _IO(VFIO_TYPE, VFIO_BASE + 5) > * > * Remove the group from the attached container. This is the > * opposite of the SET_CONTAINER call and returns the group to > * an initial state. All device file descriptors must be released > * prior to calling this interface. When removing the last group > * from a container, the IOMMU will be disabled and all state lost, > * effectively also returning the VFIO file descriptor to an initial > * state. > * Return: 0 on success, -errno on failure. > * Availability: When attached to container > */ > > So we already indicate that "all state" of the container is lost when > removing the last group, I don't see that it's necessarily to > explicitly include dirty bitmap state beyond that statement. Without > mappings there can be no dirty bitmap to track. OK :-) . > > > And any comments on other patches? thanks. > > I had a difficult time mapping the commit log to the actual code > change, I'll likely have some wording suggestions. Is patch 5/5 still > necessary if this patch is dropped? Thanks, > I think the 5th patch is still necessary. vfio_sanity_check_pfn_list() is used to check whether pfn_list of vfio_dma is empty. but we apply this check just for external domain. If the iommu backed domain also pin some pages, then this check fails. So I think we should use this check only when all domains are about to be removed. Besides, this patch should extract the "WARN_ON(iommu->notifier.head);" just for external domain. Thanks, Keqian > Alex > >>>> Fixes: d6a4c185660c ("vfio iommu: Implementation of ioctl for dirty pages tracking") >>>> Signed-off-by: Keqian Zhu >>>> --- >>>> drivers/vfio/vfio_iommu_type1.c | 14 ++++++++++++-- >>>> 1 file changed, 12 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c >>>> index 26b7eb2a5cfc..9776a059904d 100644 >>>> --- a/drivers/vfio/vfio_iommu_type1.c >>>> +++ b/drivers/vfio/vfio_iommu_type1.c >>>> @@ -2373,7 +2373,12 @@ static void vfio_iommu_type1_detach_group(void *iommu_data, >>>> if (list_empty(&iommu->external_domain->group_list)) { >>>> vfio_sanity_check_pfn_list(iommu); >>>> >>>> - if (!IS_IOMMU_CAP_DOMAIN_IN_CONTAINER(iommu)) >>>> + /* >>>> + * During dirty page tracking, we can't remove >>>> + * vfio_dma because dirty log will lose. >>>> + */ >>>> + if (!IS_IOMMU_CAP_DOMAIN_IN_CONTAINER(iommu) && >>>> + !iommu->dirty_page_tracking) >>>> vfio_iommu_unmap_unpin_all(iommu); >>>> >>>> kfree(iommu->external_domain); >>>> @@ -2406,10 +2411,15 @@ static void vfio_iommu_type1_detach_group(void *iommu_data, >>>> * iommu and external domain doesn't exist, then all the >>>> * mappings go away too. If it's the last domain with iommu and >>>> * external domain exist, update accounting >>>> + * >>>> + * Note: During dirty page tracking, we can't remove vfio_dma >>>> + * because dirty log will lose. Just update accounting is a good >>>> + * choice. >>>> */ >>>> if (list_empty(&domain->group_list)) { >>>> if (list_is_singular(&iommu->domain_list)) { >>>> - if (!iommu->external_domain) >>>> + if (!iommu->external_domain && >>>> + !iommu->dirty_page_tracking) >>>> vfio_iommu_unmap_unpin_all(iommu); >>>> else >>>> vfio_iommu_unmap_unpin_reaccount(iommu); >>> >>> . >>> >> > > . >