linux-kernel - Re: [PATCH 1/3] vfio: Introduce vma ops registration and notifier

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Date:   Wed, 17 Feb 2021 21:12:09 -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 1/3] vfio: Introduce vma ops registration and notifier

On Fri, Feb 12, 2021 at 05:20:57PM -0400, Jason Gunthorpe wrote:
> On Fri, Feb 12, 2021 at 12:27:39PM -0700, Alex Williamson wrote:
> > Create an interface through vfio-core where a vfio bus driver (ex.
> > vfio-pci) can register the vm_operations_struct it uses to map device
> > memory, along with a set of registration callbacks.  This allows
> > vfio-core to expose interfaces for IOMMU backends to match a
> > vm_area_struct to a bus driver and register a notifier for relavant
> > changes to the device mapping.  For now we define only a notifier
> > action for closing the device.
> > 
> > Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
> >  drivers/vfio/vfio.c  |  120 ++++++++++++++++++++++++++++++++++++++++++++++++++
> >  include/linux/vfio.h |   20 ++++++++
> >  2 files changed, 140 insertions(+)
> > 
> > diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
> > index 38779e6fd80c..568f5e37a95f 100644
> > +++ b/drivers/vfio/vfio.c
> > @@ -47,6 +47,8 @@ static struct vfio {
> >  	struct cdev			group_cdev;
> >  	dev_t				group_devt;
> >  	wait_queue_head_t		release_q;
> > +	struct list_head		vm_ops_list;
> > +	struct mutex			vm_ops_lock;
> >  } vfio;
> >  
> >  struct vfio_iommu_driver {
> > @@ -2354,6 +2356,121 @@ struct iommu_domain *vfio_group_iommu_domain(struct vfio_group *group)
> >  }
> >  EXPORT_SYMBOL_GPL(vfio_group_iommu_domain);
> >  
> > +struct vfio_vma_ops {
> > +	const struct vm_operations_struct	*vm_ops;
> > +	vfio_register_vma_nb_t			*reg_fn;
> > +	vfio_unregister_vma_nb_t		*unreg_fn;
> > +	struct list_head			next;
> > +};
> > +
> > +int vfio_register_vma_ops(const struct vm_operations_struct *vm_ops,
> > +			  vfio_register_vma_nb_t *reg_fn,
> > +			  vfio_unregister_vma_nb_t *unreg_fn)
> 
> This just feels a little bit too complicated
> 
> I've recently learned from Daniel that we can use the address_space
> machinery to drive the zap_vma_ptes() via unmap_mapping_range(). This
> technique replaces all the open, close and vma_list logic in vfio_pci

Here is my effort to make rdma use this, it removes a lot of ugly code:

https://github.com/jgunthorpe/linux/commits/rdma_addr_space

Still needs some more detailed testing.

This gives an option to detect vfio VMAs by checking

   if (vma->vm_file &&
       file_inode(vma->vm_file) &&
       file_inode(vma->vm_file)->i_sb->s_type == vfio_fs_type)

And all vfio VMA's can have some consistent vm_private_data, or at
worst a consistent extended vm operations struct.

Jason