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: Mon, 8 Mar 2021 11:52:18 +0800 [thread overview]
Message-ID: <0b671aef-f2b2-6162-f407-7ca5178dbebb@redhat.com> (raw)
In-Reply-To: <CACycT3uA5y=jcKPwu6rZ83Lqf1ytuPhnxWLCeMpDYrvRodHFVg@mail.gmail.com>
On 2021/3/8 11:45 上午, Yongji Xie wrote:
> On Mon, Mar 8, 2021 at 11:17 AM Jason Wang <jasowang@redhat.com> wrote:
>>
>> On 2021/3/5 3:59 下午, Yongji Xie wrote:
>>> On Fri, Mar 5, 2021 at 3:27 PM Jason Wang <jasowang@redhat.com> wrote:
>>>> 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.
>>>>
>>> But now the bounce page is mapped one by one. The second page (4096 ~
>>> 8192) might not be mapped when userspace is processing the first
>>> request. So the maximum range is 0 ~ 4096 at that time.
>>>
>>> Thanks,
>>> Yongji
>>
>> A question, if I read the code correctly, VDUSE_IOTLB_GET_FD will return
>> the whole bounce map range which is setup in vduse_dev_map_page()? So my
>> understanding is that usersapce may choose to map all its range via mmap().
>>
> Yes.
>
>> So if we 'map' bounce page one by one in vduse_dev_map_page(). (Here
>> 'map' means using multiple itree entries instead of a single one). Then
>> in the VDUSE_IOTLB_GET_FD we can keep traversing itree (dev->iommu)
>> until the range is backed by a different file.
>>
>> With this, there's no userspace visible changes and there's no need for
>> the domain->iotlb?
>>
> In this case, I wonder what range can be obtained if userspace calls
> VDUSE_IOTLB_GET_FD when the first I/O (e.g. 4K) occurs. [0, 4K] or [0,
> 64M]? In current implementation, userspace will map [0, 64M].
It should still be [0, 64M). Do you see any issue?
Thanks
>
> Thanks,
> Yongji
>
next prev parent reply other threads:[~2021-03-08 3:53 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
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 [this message]
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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