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Fri, 20 Mar 2020 12:13:53 -0700 Received: from hqmail.nvidia.com ([172.20.161.6]) by hqpgpgate101.nvidia.com (PGP Universal service); Fri, 20 Mar 2020 12:14:44 -0700 X-PGP-Universal: processed; by hqpgpgate101.nvidia.com on Fri, 20 Mar 2020 12:14:44 -0700 Received: from [10.40.103.10] (10.124.1.5) by HQMAIL107.nvidia.com (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Fri, 20 Mar 2020 19:14:36 +0000 Subject: Re: [PATCH v14 Kernel 5/7] vfio iommu: Update UNMAP_DMA ioctl to get dirty bitmap before unmap To: Alex Williamson , Yan Zhao References: <1584560474-19946-1-git-send-email-kwankhede@nvidia.com> <1584560474-19946-6-git-send-email-kwankhede@nvidia.com> <20200320083529.GA5456@joy-OptiPlex-7040> <20200320094039.4d99408d@w520.home> <20200320094727.12aba30e@w520.home> X-Nvconfidentiality: public From: Kirti Wankhede Message-ID: Date: Sat, 21 Mar 2020 00:44:32 +0530 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200320094727.12aba30e@w520.home> X-Originating-IP: [10.124.1.5] X-ClientProxiedBy: HQMAIL101.nvidia.com (172.20.187.10) To HQMAIL107.nvidia.com (172.20.187.13) Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1584731634; bh=528tuGcpedSGkPlvPwNWSbpIROZ1laa2lT/gg/YXaIg=; h=X-PGP-Universal:Subject:To:CC:References:X-Nvconfidentiality:From: Message-ID:Date:User-Agent:MIME-Version:In-Reply-To: X-Originating-IP:X-ClientProxiedBy:Content-Type:Content-Language: Content-Transfer-Encoding; b=axHbL3gw8Sdcu+OIXj4NIBQh3CzlDWLI9C4uen2Seu0T9zHCDS4pOJPqYuMpZu82w BUXy3lcF81arZL0OHNyq0wVQa5OQB/JGbfu/wf4eSAXQ3wRhO2hjlyR8fpPLAHrEdv yUQm5M4YYpvVIr1VJP1f5wtwFdu0h8NnfsDRVpM2SOE6xMFmHUpB/P+5nnJcnP1Dix p9xGt28b11xGTwVzrjqxXytzJ6xbvRasbzRvm80b6xAFWBmY56E4+LEtZEGJmm+Byf +5goJjLtKuunOzKi7Ci2WwNEBjqw5LpwN35+/mLnB76NhU7UUnr4ey7/LZWlLylvJY cqjYXZNhgZSDQ== X-detected-operating-system: by eggs.gnu.org: Windows 7 or 8 [fuzzy] X-Received-From: 216.228.121.64 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "Zhengxiao.zx@Alibaba-inc.com" , "Tian, Kevin" , "Liu, Yi L" , "cjia@nvidia.com" , "kvm@vger.kernel.org" , "eskultet@redhat.com" , "Yang, Ziye" , "qemu-devel@nongnu.org" , "cohuck@redhat.com" , "shuangtai.tst@alibaba-inc.com" , "dgilbert@redhat.com" , "Wang, Zhi A" , "mlevitsk@redhat.com" , "pasic@linux.ibm.com" , "aik@ozlabs.ru" , "eauger@redhat.com" , "felipe@nutanix.com" , "jonathan.davies@nutanix.com" , "Liu, Changpeng" , "Ken.Xue@amd.com" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 3/20/2020 9:17 PM, Alex Williamson wrote: > On Fri, 20 Mar 2020 09:40:39 -0600 > Alex Williamson wrote: > >> On Fri, 20 Mar 2020 04:35:29 -0400 >> Yan Zhao wrote: >> >>> On Thu, Mar 19, 2020 at 03:41:12AM +0800, Kirti Wankhede wrote: >>>> DMA mapped pages, including those pinned by mdev vendor drivers, might >>>> get unpinned and unmapped while migration is active and device is still >>>> running. For example, in pre-copy phase while guest driver could access >>>> those pages, host device or vendor driver can dirty these mapped pages. >>>> Such pages should be marked dirty so as to maintain memory consistency >>>> for a user making use of dirty page tracking. >>>> >>>> To get bitmap during unmap, user should set flag >>>> VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP, bitmap memory should be allocated and >>>> zeroed by user space application. Bitmap size and page size should be set >>>> by user application. >>>> >>>> Signed-off-by: Kirti Wankhede >>>> Reviewed-by: Neo Jia >>>> --- >>>> drivers/vfio/vfio_iommu_type1.c | 55 ++++++++++++++++++++++++++++++++++++++--- >>>> include/uapi/linux/vfio.h | 11 +++++++++ >>>> 2 files changed, 62 insertions(+), 4 deletions(-) >>>> >>>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c >>>> index d6417fb02174..aa1ac30f7854 100644 >>>> --- a/drivers/vfio/vfio_iommu_type1.c >>>> +++ b/drivers/vfio/vfio_iommu_type1.c >>>> @@ -939,7 +939,8 @@ static int verify_bitmap_size(uint64_t npages, uint64_t bitmap_size) >>>> } >>>> >>>> static int vfio_dma_do_unmap(struct vfio_iommu *iommu, >>>> - struct vfio_iommu_type1_dma_unmap *unmap) >>>> + struct vfio_iommu_type1_dma_unmap *unmap, >>>> + struct vfio_bitmap *bitmap) >>>> { >>>> uint64_t mask; >>>> struct vfio_dma *dma, *dma_last = NULL; >>>> @@ -990,6 +991,10 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu, >>>> * will be returned if these conditions are not met. The v2 interface >>>> * will only return success and a size of zero if there were no >>>> * mappings within the range. >>>> + * >>>> + * When VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP flag is set, unmap request >>>> + * must be for single mapping. Multiple mappings with this flag set is >>>> + * not supported. >>>> */ >>>> if (iommu->v2) { >>>> dma = vfio_find_dma(iommu, unmap->iova, 1); >>>> @@ -997,6 +1002,13 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu, >>>> ret = -EINVAL; >>>> goto unlock; >>>> } >>>> + >>>> + if ((unmap->flags & VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP) && >>>> + (dma->iova != unmap->iova || dma->size != unmap->size)) { >>> dma is probably NULL here! >> >> Yep, I didn't look closely enough there. This is situated right >> between the check to make sure we're not bisecting a mapping at the >> start of the unmap and the check to make sure we're not bisecting a >> mapping at the end of the unmap. There's no guarantee that we have a >> valid pointer here. The test should be in the while() loop below this >> code. > > Actually the test could remain here, we can exit here if we can't find > a dma at the start of the unmap range with the GET_DIRTY_BITMAP flag, > but we absolutely cannot deref dma without testing it. > In the check above newly added check, if dma is NULL then its an error condition, because Unmap requests must fully cover previous mappings, right? >>> And this restriction on UNMAP would make some UNMAP operations of vIOMMU >>> fail. >>> >>> e.g. below condition indeed happens in reality. >>> an UNMAP ioctl comes for IOVA range from 0xff800000, of size 0x200000 >>> However, IOVAs in this range are mapped page by page.i.e., dma->size is 0x1000. >>> >>> Previous, this UNMAP ioctl could unmap successfully as a whole. >> >> What triggers this in the guest? Note that it's only when using the >> GET_DIRTY_BITMAP flag that this is restricted. Does the event you're >> referring to potentially occur under normal circumstances in that mode? >> Thanks, >> Such unmap would callback vfio_iommu_map_notify() in QEMU. In vfio_iommu_map_notify(), unmap is called on same range addr_mask + 1> which was used for map. Secondly unmap with bitmap will be called only when device state has _SAVING flag set. Thanks, Kirti