linux-kernel - Re: [RFC PATCH 05/10] vfio: Create a vfio

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Date:   Mon, 22 Feb 2021 13:29:13 -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: [RFC PATCH 05/10] vfio: Create a vfio_device from vma lookup

On Mon, Feb 22, 2021 at 09:51:25AM -0700, Alex Williamson wrote:

> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
> index da212425ab30..399c42b77fbb 100644
> +++ b/drivers/vfio/vfio.c
> @@ -572,6 +572,15 @@ void vfio_device_unmap_mapping_range(struct vfio_device *device,
>  }
>  EXPORT_SYMBOL_GPL(vfio_device_unmap_mapping_range);
>  
> +/*
> + * A VFIO bus driver using this open callback will provide a
> + * struct vfio_device pointer in the vm_private_data field.

The vfio_device pointer should be stored in the struct file

> +struct vfio_device *vfio_device_get_from_vma(struct vm_area_struct *vma)
> +{
> +	struct vfio_device *device;
> +
> +	if (vma->vm_ops->open != vfio_device_vma_open)
> +		return ERR_PTR(-ENODEV);
> +

Having looked at VFIO alot more closely last week, this is even more
trivial - VFIO only creates mmaps of memory we want to invalidate, so
this is just very simple:

struct vfio_device *vfio_device_get_from_vma(struct vm_area_struct *vma)
{
       if (!vma->vm_file ||vma->vm_file->f_op != &vfio_device_fops)
	   return ERR_PTR(-ENODEV);
       return vma->vm_file->f_private;
}

The only use of the special ops would be if there are multiple types
of mmap's going on, but for this narrow use case those would be safely
distinguished by the vm_pgoff instead

> +extern void vfio_device_vma_open(struct vm_area_struct *vma);
> +extern struct vfio_device *vfio_device_get_from_vma(struct vm_area_struct *vma);

No externs on function prototypes in new code please, we've been
slowly deleting them..

Jason