From: Jason Wang <jasowang@redhat.com>
To: Yongji Xie <xieyongji@bytedance.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>,
Stefan Hajnoczi <stefanha@redhat.com>,
Stefano Garzarella <sgarzare@redhat.com>,
Parav Pandit <parav@nvidia.com>, Bob Liu <bob.liu@oracle.com>,
Christoph Hellwig <hch@infradead.org>,
Randy Dunlap <rdunlap@infradead.org>,
Matthew Wilcox <willy@infradead.org>,
viro@zeniv.linux.org.uk, Jens Axboe <axboe@kernel.dk>,
bcrl@kvack.org, Jonathan Corbet <corbet@lwn.net>,
virtualization@lists.linux-foundation.org,
netdev@vger.kernel.org, kvm@vger.kernel.org, linux-aio@kvack.org,
linux-fsdevel@vger.kernel.org
Subject: Re: [RFC v4 06/11] vduse: Implement an MMU-based IOMMU driver
Date: Fri, 5 Mar 2021 15:27:11 +0800 [thread overview]
Message-ID: <2652f696-faf7-26eb-a8b2-c4cfe3aaed15@redhat.com> (raw)
In-Reply-To: <CACycT3sUJNmi2BdLsi3W72+qTKQaCo_nQYu-fdxg9y4pAvBMow@mail.gmail.com>
On 2021/3/5 3:13 下午, Yongji Xie wrote:
> On Fri, Mar 5, 2021 at 2:52 PM Jason Wang <jasowang@redhat.com> wrote:
>>
>> On 2021/3/5 2:15 下午, Yongji Xie wrote:
>>
>> Sorry if I've asked this before.
>>
>> But what's the reason for maintaing a dedicated IOTLB here? I think we
>> could reuse vduse_dev->iommu since the device can not be used by both
>> virtio and vhost in the same time or use vduse_iova_domain->iotlb for
>> set_map().
>>
>> The main difference between domain->iotlb and dev->iotlb is the way to
>> deal with bounce buffer. In the domain->iotlb case, bounce buffer
>> needs to be mapped each DMA transfer because we need to get the bounce
>> pages by an IOVA during DMA unmapping. In the dev->iotlb case, bounce
>> buffer only needs to be mapped once during initialization, which will
>> be used to tell userspace how to do mmap().
>>
>> Also, since vhost IOTLB support per mapping token (opauqe), can we use
>> that instead of the bounce_pages *?
>>
>> Sorry, I didn't get you here. Which value do you mean to store in the
>> opaque pointer?
>>
>> So I would like to have a way to use a single IOTLB for manage all kinds
>> of mappings. Two possible ideas:
>>
>> 1) map bounce page one by one in vduse_dev_map_page(), in
>> VDUSE_IOTLB_GET_FD, try to merge the result if we had the same fd. Then
>> for bounce pages, userspace still only need to map it once and we can
>> maintain the actual mapping by storing the page or pa in the opaque
>> field of IOTLB entry.
>>
>> Looks like userspace still needs to unmap the old region and map a new
>> region (size is changed) with the fd in each VDUSE_IOTLB_GET_FD ioctl.
>>
>>
>> I don't get here. Can you give an example?
>>
> For example, userspace needs to process two I/O requests (one page per
> request). To process the first request, userspace uses
> VDUSE_IOTLB_GET_FD ioctl to query the iova region (0 ~ 4096) and mmap
> it.
I think in this case we should let VDUSE_IOTLB_GET_FD return the maximum
range as far as they are backed by the same fd.
In the case of bounce page, it's bascially the whole range of bounce buffer?
Thanks
> To process the second request, userspace uses VDUSE_IOTLB_GET_FD
> ioctl to query the new iova region and map a new region (0 ~ 8192).
> Then userspace needs to traverse the list of iova regions and unmap
> the old region (0 ~ 4096). Looks like this is a little complex.
>
> Thanks,
> Yongji
>
next prev parent reply other threads:[~2021-03-05 7:27 UTC|newest]
Thread overview: 65+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-23 11:50 [RFC v4 00/11] Introduce VDUSE - vDPA Device in Userspace Xie Yongji
2021-02-23 11:50 ` [RFC v4 01/11] eventfd: Increase the recursion depth of eventfd_signal() Xie Yongji
2021-03-02 6:44 ` Jason Wang
2021-03-02 10:32 ` Yongji Xie
2021-02-23 11:50 ` [RFC v4 02/11] vhost-vdpa: protect concurrent access to vhost device iotlb Xie Yongji
2021-03-02 6:47 ` Jason Wang
2021-03-02 10:20 ` Yongji Xie
2021-02-23 11:50 ` [RFC v4 03/11] vhost-iotlb: Add an opaque pointer for vhost IOTLB Xie Yongji
2021-03-02 6:49 ` Jason Wang
2021-02-23 11:50 ` [RFC v4 04/11] vdpa: Add an opaque pointer for vdpa_config_ops.dma_map() Xie Yongji
2021-03-02 6:50 ` Jason Wang
2021-02-23 11:50 ` [RFC v4 05/11] vdpa: Support transferring virtual addressing during DMA mapping Xie Yongji
2021-03-03 10:52 ` Mika Penttilä
2021-03-03 12:45 ` Yongji Xie
2021-03-03 13:38 ` Mika Penttilä
2021-03-04 3:07 ` Jason Wang
2021-03-04 5:40 ` Yongji Xie
2021-02-23 11:50 ` [RFC v4 06/11] vduse: Implement an MMU-based IOMMU driver Xie Yongji
2021-03-04 4:20 ` Jason Wang
2021-03-04 5:12 ` Yongji Xie
2021-03-05 3:35 ` Jason Wang
2021-03-05 6:15 ` Yongji Xie
[not found] ` <4db35f8c-ee3a-90fb-8d14-5d6014b4f6fa@redhat.com>
2021-03-05 7:13 ` Yongji Xie
2021-03-05 7:27 ` Jason Wang [this message]
2021-03-05 7:59 ` Yongji Xie
2021-03-08 3:17 ` Jason Wang
2021-03-08 3:45 ` Yongji Xie
2021-03-08 3:52 ` Jason Wang
2021-03-08 5:05 ` Yongji Xie
2021-03-08 7:04 ` Jason Wang
2021-03-08 7:08 ` Yongji Xie
2021-02-23 11:50 ` [RFC v4 07/11] vduse: Introduce VDUSE - vDPA Device in Userspace Xie Yongji
2021-03-04 6:27 ` Jason Wang
2021-03-04 8:05 ` Yongji Xie
2021-03-05 3:20 ` Jason Wang
2021-03-05 3:49 ` Yongji Xie
2021-03-10 12:58 ` Jason Wang
2021-03-11 2:28 ` Yongji Xie
2021-02-23 11:50 ` [RFC v4 08/11] vduse: Add config interrupt support Xie Yongji
2021-02-23 11:50 ` [RFC v4 09/11] Documentation: Add documentation for VDUSE Xie Yongji
2021-03-04 6:39 ` Jason Wang
2021-03-04 10:35 ` Yongji Xie
2021-02-23 11:50 ` [RFC v4 10/11] vduse: Introduce a workqueue for irq injection Xie Yongji
2021-03-04 6:59 ` Jason Wang
2021-03-04 8:58 ` Yongji Xie
2021-03-05 3:04 ` Jason Wang
2021-03-05 3:30 ` Yongji Xie
2021-03-05 3:42 ` Jason Wang
2021-03-05 6:36 ` Yongji Xie
2021-03-05 7:01 ` Jason Wang
2021-03-05 7:27 ` Yongji Xie
2021-03-05 7:36 ` Jason Wang
2021-03-05 8:12 ` Yongji Xie
2021-03-08 3:04 ` Jason Wang
2021-03-08 4:50 ` Yongji Xie
2021-03-08 7:01 ` Jason Wang
2021-03-08 7:16 ` Yongji Xie
2021-03-08 7:29 ` Jason Wang
2021-02-23 11:50 ` [RFC v4 11/11] vduse: Support binding irq to the specified cpu Xie Yongji
2021-03-04 7:30 ` Jason Wang
2021-03-04 8:19 ` Yongji Xie
2021-03-05 3:11 ` Jason Wang
2021-03-05 3:37 ` Yongji Xie
2021-03-05 3:44 ` Jason Wang
2021-03-05 6:40 ` Yongji Xie
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