linux-kernel - Re: [RFC v2 2/4] vduse: Add file operation for mmap

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Message-ID: <CACGkMEuOYWYYGta5VoZaURVxrBFwU+1aNwoh7RyT1woQCNHJtg@mail.gmail.com>
Date:   Mon, 18 Sep 2023 16:46:18 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Cindy Lu <lulu@...hat.com>
Cc:     mst@...hat.com, maxime.coquelin@...hat.com,
        xieyongji@...edance.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [RFC v2 2/4] vduse: Add file operation for mmap

On Tue, Sep 12, 2023 at 11:00 AM Cindy Lu <lulu@...hat.com> wrote:
>
> Add the operation for mmap, The user space APP will
> use this function to map the pages to userspace
>
> Signed-off-by: Cindy Lu <lulu@...hat.com>
> ---
>  drivers/vdpa/vdpa_user/vduse_dev.c | 63 ++++++++++++++++++++++++++++++
>  1 file changed, 63 insertions(+)
>
> diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
> index 4c256fa31fc4..2c69f4004a6e 100644
> --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> @@ -1388,6 +1388,67 @@ static struct vduse_dev *vduse_dev_get_from_minor(int minor)
>         return dev;
>  }
>
> +static vm_fault_t vduse_vm_fault(struct vm_fault *vmf)
> +{
> +       struct vduse_dev *dev = vmf->vma->vm_file->private_data;
> +       struct vm_area_struct *vma = vmf->vma;
> +       u16 index = vma->vm_pgoff;
> +       struct vduse_virtqueue *vq;
> +       struct vdpa_reconnect_info *info;
> +
> +       if (index == 0) {
> +               info = &dev->reconnect_status;
> +       } else {
> +               vq = &dev->vqs[index - 1];
> +               info = &vq->reconnect_info;
> +       }
> +       vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
> +       if (remap_pfn_range(vma, vmf->address & PAGE_MASK, PFN_DOWN(info->addr),
> +                           PAGE_SIZE, vma->vm_page_prot))
> +               return VM_FAULT_SIGBUS;
> +       return VM_FAULT_NOPAGE;
> +}
> +
> +static const struct vm_operations_struct vduse_vm_ops = {
> +       .fault = vduse_vm_fault,
> +};
> +
> +static int vduse_dev_mmap(struct file *file, struct vm_area_struct *vma)
> +{
> +       struct vduse_dev *dev = file->private_data;
> +       struct vdpa_reconnect_info *info;
> +       unsigned long index = vma->vm_pgoff;
> +       struct vduse_virtqueue *vq;
> +
> +       if (vma->vm_end - vma->vm_start != PAGE_SIZE)
> +               return -EINVAL;
> +       if ((vma->vm_flags & VM_SHARED) == 0)
> +               return -EINVAL;
> +
> +       if (index > 65535)
> +               return -EINVAL;
> +
> +       if (index == 0) {
> +               info = &dev->reconnect_status;
> +       } else {
> +               vq = &dev->vqs[index - 1];
> +               info = &vq->reconnect_info;
> +       }
> +
> +       if (info->index != index)
> +               return -EINVAL;

Under which case could we meet this?

> +
> +       if (info->addr & (PAGE_SIZE - 1))
> +               return -EINVAL;

And this?

> +       if (vma->vm_end - vma->vm_start != info->size)
> +               return -EOPNOTSUPP;
> +
> +       vm_flags_set(vma, VM_IO | VM_PFNMAP | VM_DONTDUMP);

Why do you use VM_IO, VM_PFNMAP and VM_DONTDUMP?

Thanks

> +       vma->vm_ops = &vduse_vm_ops;
> +
> +       return 0;
> +}
> +
>  static int vduse_dev_open(struct inode *inode, struct file *file)
>  {
>         int ret;
> @@ -1420,6 +1481,8 @@ static const struct file_operations vduse_dev_fops = {
>         .unlocked_ioctl = vduse_dev_ioctl,
>         .compat_ioctl   = compat_ptr_ioctl,
>         .llseek         = noop_llseek,
> +       .mmap           = vduse_dev_mmap,
> +
>  };
>
>  static struct vduse_dev *vduse_dev_create(void)
> --
> 2.34.3
>