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From:   Cindy Lu <lulu@redhat.com>
Date:   Sat, 1 Jul 2023 17:23:29 +0800
Message-ID: <CACLfguXHpCVuU-X9XZBOsuusELVBQsTa0L5LiJ59BSuiNx=ARg@mail.gmail.com>
Subject: Re: [RFC 2/4] vduse: Add file operation for mmap
To:     Jason Wang <jasowang@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 4:08=E2=80=AFPM Jason Wang <jasowang@redhat.com> wr=
ote:
>
> 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 mm=
ap.
>
> >
> > 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_use=
r/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_mino=
r(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(inf=
o->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).
>
yes, this map the separate pages per vq, beads on my test this works
> > +               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?
>
I had hard code the size in userpace , I will add the new ioctl of get
the map size
Thanks
cindy
> > +
> > +       vm_flags_set(vma, VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDU=
MP);
>
> 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_fop=
s =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
> >
>