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From:   Jason Wang <jasowang@redhat.com>
Date:   Wed, 28 Jun 2023 16:08:39 +0800
Message-ID: <CACGkMEuzrFP96qcFL0M=nGiQ9t57-EzOhZmB3No-8T8pMAWTxw@mail.gmail.com>
Subject: Re: [RFC 2/4] vduse: Add file operation for mmap
To:     Cindy Lu <lulu@redhat.com>
Cc:     mst@redhat.com, maxime.coquelin@redhat.com,
        xieyongji@bytedance.com, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        virtualization@lists.linux-foundation.org, netdev@vger.kernel.org
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On Wed, Jun 28, 2023 at 2:59=E2=80=AFPM Cindy Lu <lulu@redhat.com> wrote:
>
> From: Your Name <you@example.com>
>
> Add the operation for mmap, The user space APP will
> use this function to map the pages to userspace

Please be specific in the log. E.g why and what the main goal for this mmap=
.

>
> Signed-off-by: Cindy Lu <lulu@redhat.com>
> ---
>  drivers/vdpa/vdpa_user/vduse_dev.c | 49 ++++++++++++++++++++++++++++++
>  1 file changed, 49 insertions(+)
>
> diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/=
vduse_dev.c
> index f845dc46b1db..1b833bf0ae37 100644
> --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> @@ -1313,6 +1313,54 @@ 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 =3D vmf->vma->vm_file->private_data;
> +       struct vm_area_struct *vma =3D vmf->vma;
> +       u16 index =3D vma->vm_pgoff;
> +
> +       struct vdpa_reconnect_info *info;
> +       info =3D &dev->reconnect_info[index];
> +
> +       vma->vm_page_prot =3D 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))

I'm not sure if this can work e.g do we want to use separate pages for
each virtqueue (I think the answer is yes).

> +               return VM_FAULT_SIGBUS;
> +       return VM_FAULT_NOPAGE;
> +}
> +
> +static const struct vm_operations_struct vduse_vm_ops =3D {
> +       .fault =3D vduse_vm_fault,
> +};
> +
> +static int vduse_mmap(struct file *file, struct vm_area_struct *vma)
> +{
> +       struct vduse_dev *dev =3D file->private_data;
> +       struct vdpa_reconnect_info *info;
> +       unsigned long index =3D vma->vm_pgoff;
> +
> +       if (vma->vm_end - vma->vm_start !=3D PAGE_SIZE)
> +               return -EINVAL;
> +       if ((vma->vm_flags & VM_SHARED) =3D=3D 0)
> +               return -EINVAL;
> +
> +       if (index > 65535)
> +               return -EINVAL;
> +
> +       info =3D &dev->reconnect_info[index];
> +       if (info->addr & (PAGE_SIZE - 1))
> +               return -EINVAL;
> +       if (vma->vm_end - vma->vm_start !=3D info->size) {
> +               return -ENOTSUPP;
> +       }

How can userspace know the correct size (info->size) here?

> +
> +       vm_flags_set(vma, VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP=
);

Why do you need VM_IO, VM_PFNMAP and VM_DONTDUMP here?

Thanks

> +       vma->vm_ops =3D &vduse_vm_ops;
> +
> +       return 0;
> +}
> +
>  static int vduse_dev_open(struct inode *inode, struct file *file)
>  {
>         int ret;
> @@ -1345,6 +1393,7 @@ static const struct file_operations vduse_dev_fops =
=3D {
>         .unlocked_ioctl =3D vduse_dev_ioctl,
>         .compat_ioctl   =3D compat_ptr_ioctl,
>         .llseek         =3D noop_llseek,
> +       .mmap           =3D vduse_mmap,
>  };
>
>  static struct vduse_dev *vduse_dev_create(void)
> --
> 2.34.3
>