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Date: Fri, 25 Dec 2020 14:57:59 +0800 From: Jason Wang <jasowang@...hat.com> To: Yongji Xie <xieyongji@...edance.com> Cc: "Michael S. Tsirkin" <mst@...hat.com>, Stefan Hajnoczi <stefanha@...hat.com>, sgarzare@...hat.com, Parav Pandit <parav@...dia.com>, akpm@...ux-foundation.org, Randy Dunlap <rdunlap@...radead.org>, Matthew Wilcox <willy@...radead.org>, viro@...iv.linux.org.uk, axboe@...nel.dk, bcrl@...ck.org, corbet@....net, virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org, kvm@...r.kernel.org, linux-aio@...ck.org, linux-fsdevel@...r.kernel.org, linux-mm@...ck.org Subject: Re: [RFC v2 09/13] vduse: Add support for processing vhost iotlb message On 2020/12/24 下午3:37, Yongji Xie wrote: > On Thu, Dec 24, 2020 at 10:41 AM Jason Wang <jasowang@...hat.com> wrote: >> >> On 2020/12/23 下午8:14, Yongji Xie wrote: >>> On Wed, Dec 23, 2020 at 5:05 PM Jason Wang <jasowang@...hat.com> wrote: >>>> On 2020/12/22 下午10:52, Xie Yongji wrote: >>>>> To support vhost-vdpa bus driver, we need a way to share the >>>>> vhost-vdpa backend process's memory with the userspace VDUSE process. >>>>> >>>>> This patch tries to make use of the vhost iotlb message to achieve >>>>> that. We will get the shm file from the iotlb message and pass it >>>>> to the userspace VDUSE process. >>>>> >>>>> Signed-off-by: Xie Yongji <xieyongji@...edance.com> >>>>> --- >>>>> Documentation/driver-api/vduse.rst | 15 +++- >>>>> drivers/vdpa/vdpa_user/vduse_dev.c | 147 ++++++++++++++++++++++++++++++++++++- >>>>> include/uapi/linux/vduse.h | 11 +++ >>>>> 3 files changed, 171 insertions(+), 2 deletions(-) >>>>> >>>>> diff --git a/Documentation/driver-api/vduse.rst b/Documentation/driver-api/vduse.rst >>>>> index 623f7b040ccf..48e4b1ba353f 100644 >>>>> --- a/Documentation/driver-api/vduse.rst >>>>> +++ b/Documentation/driver-api/vduse.rst >>>>> @@ -46,13 +46,26 @@ The following types of messages are provided by the VDUSE framework now: >>>>> >>>>> - VDUSE_GET_CONFIG: Read from device specific configuration space >>>>> >>>>> +- VDUSE_UPDATE_IOTLB: Update the memory mapping in device IOTLB >>>>> + >>>>> +- VDUSE_INVALIDATE_IOTLB: Invalidate the memory mapping in device IOTLB >>>>> + >>>>> Please see include/linux/vdpa.h for details. >>>>> >>>>> -In the data path, VDUSE framework implements a MMU-based on-chip IOMMU >>>>> +The data path of userspace vDPA device is implemented in different ways >>>>> +depending on the vdpa bus to which it is attached. >>>>> + >>>>> +In virtio-vdpa case, VDUSE framework implements a MMU-based on-chip IOMMU >>>>> driver which supports mapping the kernel dma buffer to a userspace iova >>>>> region dynamically. The userspace iova region can be created by passing >>>>> the userspace vDPA device fd to mmap(2). >>>>> >>>>> +In vhost-vdpa case, the dma buffer is reside in a userspace memory region >>>>> +which will be shared to the VDUSE userspace processs via the file >>>>> +descriptor in VDUSE_UPDATE_IOTLB message. And the corresponding address >>>>> +mapping (IOVA of dma buffer <-> VA of the memory region) is also included >>>>> +in this message. >>>>> + >>>>> Besides, the eventfd mechanism is used to trigger interrupt callbacks and >>>>> receive virtqueue kicks in userspace. The following ioctls on the userspace >>>>> vDPA device fd are provided to support that: >>>>> diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c >>>>> index b974333ed4e9..d24aaacb6008 100644 >>>>> --- a/drivers/vdpa/vdpa_user/vduse_dev.c >>>>> +++ b/drivers/vdpa/vdpa_user/vduse_dev.c >>>>> @@ -34,6 +34,7 @@ >>>>> >>>>> struct vduse_dev_msg { >>>>> struct vduse_dev_request req; >>>>> + struct file *iotlb_file; >>>>> struct vduse_dev_response resp; >>>>> struct list_head list; >>>>> wait_queue_head_t waitq; >>>>> @@ -325,12 +326,80 @@ static int vduse_dev_set_vq_state(struct vduse_dev *dev, >>>>> return ret; >>>>> } >>>>> >>>>> +static int vduse_dev_update_iotlb(struct vduse_dev *dev, struct file *file, >>>>> + u64 offset, u64 iova, u64 size, u8 perm) >>>>> +{ >>>>> + struct vduse_dev_msg *msg; >>>>> + int ret; >>>>> + >>>>> + if (!size) >>>>> + return -EINVAL; >>>>> + >>>>> + msg = vduse_dev_new_msg(dev, VDUSE_UPDATE_IOTLB); >>>>> + msg->req.size = sizeof(struct vduse_iotlb); >>>>> + msg->req.iotlb.offset = offset; >>>>> + msg->req.iotlb.iova = iova; >>>>> + msg->req.iotlb.size = size; >>>>> + msg->req.iotlb.perm = perm; >>>>> + msg->req.iotlb.fd = -1; >>>>> + msg->iotlb_file = get_file(file); >>>>> + >>>>> + ret = vduse_dev_msg_sync(dev, msg); >>>> My feeling is that we should provide consistent API for the userspace >>>> device to use. >>>> >>>> E.g we'd better carry the IOTLB message for both virtio/vhost drivers. >>>> >>>> It looks to me for virtio drivers we can still use UPDAT_IOTLB message >>>> by using VDUSE file as msg->iotlb_file here. >>>> >>> It's OK for me. One problem is when to transfer the UPDATE_IOTLB >>> message in virtio cases. >> >> Instead of generating IOTLB messages for userspace. >> >> How about record the mappings (which is a common case for device have >> on-chip IOMMU e.g mlx5e and vdpa simlator), then we can introduce ioctl >> for userspace to query? >> > If so, the IOTLB UPDATE is actually triggered by ioctl, but > IOTLB_INVALIDATE is triggered by the message. Is it a little odd? Good point. Some questions here: 1) Userspace think the IOTLB was flushed after IOTLB_INVALIDATE syscall is returned. But this patch doesn't have this guarantee. Can this lead some issues? 2) I think after VDUSE userspace receives IOTLB_INVALIDATE, it needs to issue a munmap(). What if it doesn't do that? > Or > how about trigger it when userspace call mmap() on the device fd? One possible issue is that the IOTLB_UPDATE/INVALIDATE might come after mmap(): 1) When vIOMMU is enabled 2) Guest memory topology has been changed (memory hotplug). Thanks > > Thanks, > Yongji >
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