linux-kernel - Re: [PATCH v2 2/5] vduse: Add file operation for mmap

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Message-ID: <CACGkMEsSAvUpkxCutX69fPS5B5ChEUP+KutP1OtgcWE6Job61g@mail.gmail.com>
Date:   Tue, 21 Nov 2023 15:40:16 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Cindy Lu <lulu@...hat.com>
Cc:     mst@...hat.com, xieyongji@...edance.com,
        linux-kernel@...r.kernel.org, maxime.coquelin@...hat.com
Subject: Re: [PATCH v2 2/5] vduse: Add file operation for mmap

On Tue, Nov 21, 2023 at 3:31 PM 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 | 79 ++++++++++++++++++++++++++++++
>  1 file changed, 79 insertions(+)
>
> diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
> index 6209e2f00278..ccb30e98bab5 100644
> --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> @@ -1376,6 +1376,83 @@ 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;
> +
> +       /* index 0  page reserved for vduse status*/
> +       if (index == 0) {
> +               info = &dev->reconnect_info;
> +       } else {
> +               /* index 1+vq_number page reserved for vduse vqs*/
> +               vq = &dev->vqs[index - 1];
> +               info = &vq->reconnect_info;
> +       }
> +       if (remap_pfn_range(vma, vmf->address & PAGE_MASK,
> +                           PFN_DOWN(virt_to_phys((void *)info->vaddr)),
> +                           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;
> +
> +       /*check if Userspace App map the page number larger than kernel allocated*/
> +       if (index > dev->vq_num + 1)
> +               return -EINVAL;
> +
> +       /* index 0  page reserved for vduse status*/
> +       if (index == 0) {
> +               info = &dev->reconnect_info;
> +       } else {
> +               /* index 1+vq_number page reserved for vduse vqs*/
> +               vq = &dev->vqs[index - 1];
> +               info = &vq->reconnect_info;
> +       }
> +       /*check if map pages was allocated and inited by kernel */
> +       if (info->vaddr == 0)
> +               return -EOPNOTSUPP;
> +
> +       /* check if the address is page aligned, if not,
> +        * this address maybe damaged
> +        */
> +       if (virt_to_phys((void *)info->vaddr) & (PAGE_SIZE - 1))
> +               return -EINVAL;
> +
> +       /* check if Userspace App mapped the correct size
> +        * the userspace App should map one page each time
> +        */
> +       if (vma->vm_end - vma->vm_start != PAGE_SIZE)
> +               return -EOPNOTSUPP;
> +       /* VM_IO: set as a memory-mapped I/O region,This will for vq information
> +        * VM_PFNMAP: only need  the pure PFN
> +        * VM_DONTEXPAND: do not need to use mremap() in this function
> +        * VM_DONTDUMP:Do not include in the core dump
> +        */

Instead of duplicating the semantic, you need to explain why it is needed.

For example I don't see how the following is useful:

VM_IO: the page is not backed by any I/O page
VM_PFNMAP: we need map it to usespace for sure, for it's not a pure PFN
VM_DONTDUMP: including this in core dump may help to debug the
userspace process for sure

Thanks

> +       vm_flags_set(vma, VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP);
> +       vma->vm_ops = &vduse_vm_ops;
> +
> +       return 0;
> +}
> +
>  static int vduse_dev_open(struct inode *inode, struct file *file)
>  {
>         int ret;
> @@ -1408,6 +1485,8 @@ 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
>