linux-kernel - Re: [PATCH v1 06/14] vfio: Add vma to pfn callback

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Message-ID: <20210309003344.GC4247@nvidia.com>
Date:   Mon, 8 Mar 2021 20:33:44 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     cohuck@...hat.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, peterx@...hat.com
Subject: Re: [PATCH v1 06/14] vfio: Add vma to pfn callback

On Mon, Mar 08, 2021 at 02:48:16PM -0700, Alex Williamson wrote:
> Add a new vfio_device_ops callback to allow the bus driver to
> translate a vma mapping of a vfio device fd to a pfn.  Plumb through
> vfio-core.  Implemented for vfio-pci.
> 
> Suggested-by: Jason Gunthorpe <jgg@...dia.com>
> Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
>  drivers/vfio/pci/vfio_pci.c |    1 +
>  drivers/vfio/vfio.c         |   16 ++++++++++++++++
>  include/linux/vfio.h        |    3 +++
>  3 files changed, 20 insertions(+)
> 
> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> index 415b5109da9b..585895970e9c 100644
> +++ b/drivers/vfio/pci/vfio_pci.c
> @@ -1756,6 +1756,7 @@ static const struct vfio_device_ops vfio_pci_ops = {
>  	.mmap		= vfio_pci_mmap,
>  	.request	= vfio_pci_request,
>  	.match		= vfio_pci_match,
> +	.vma_to_pfn	= vfio_pci_bar_vma_to_pfn,
>  };
>  
>  static int vfio_pci_reflck_attach(struct vfio_pci_device *vdev);
> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
> index 3a3e85a0dc3e..c47895539a1a 100644
> +++ b/drivers/vfio/vfio.c
> @@ -944,6 +944,22 @@ struct vfio_device *vfio_device_get_from_vma(struct vm_area_struct *vma)
>  }
>  EXPORT_SYMBOL_GPL(vfio_device_get_from_vma);
>  
> +int vfio_vma_to_pfn(struct vm_area_struct *vma, unsigned long *pfn)
> +{
> +	struct vfio_device *device;
> +
> +	if (!vma->vm_file || vma->vm_file->f_op != &vfio_device_fops)
> +		return -EINVAL;
> +
> +	device = vma->vm_file->private_data;

Since the caller has the vfio_device already I would pass in the
vfio_device here rather than look it up again.

If you are really worried about API mis-use then use a protective
assertion like this:

  if (WARN_ON(vma->vm_file->private_data != device))
        return -EINVAL;

Jason