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Fri, 20 Mar 2020 19:28:24 +0000 (UTC) Received: from w520.home (ovpn-112-162.phx2.redhat.com [10.3.112.162]) by smtp.corp.redhat.com (Postfix) with ESMTP id 311DB73897; Fri, 20 Mar 2020 19:28:22 +0000 (UTC) Date: Fri, 20 Mar 2020 13:28:21 -0600 From: Alex Williamson To: Kirti Wankhede Subject: Re: [PATCH v14 Kernel 5/7] vfio iommu: Update UNMAP_DMA ioctl to get dirty bitmap before unmap Message-ID: <20200320132821.2fe80c29@w520.home> In-Reply-To: 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> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 63.128.21.74 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" , Yan Zhao , "Liu, Changpeng" , "Ken.Xue@amd.com" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Sat, 21 Mar 2020 00:44:32 +0530 Kirti Wankhede wrote: > 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? Yes, but we'll do a null pointer deref before we return error. > >>> 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 iotlb->addr_mask + 1> which was used for map. Secondly unmap with bitmap > will be called only when device state has _SAVING flag set. It might be helpful for Yan, and everyone else, to see the latest QEMU patch series. Thanks, Alex