linux-kernel - Re: [PATCH 4/7] vfio,vfio-pci: Add vma to pfn callback

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Date:   Thu, 5 Aug 2021 22:01:46 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        peterx@...hat.com
Subject: Re: [PATCH 4/7] vfio,vfio-pci: Add vma to pfn callback

On Thu, Aug 05, 2021 at 11:07:47AM -0600, Alex Williamson wrote:
> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
> index 1e4fc69fee7d..42ca93be152a 100644
> +++ b/drivers/vfio/vfio.c
> @@ -875,6 +875,22 @@ struct vfio_device *vfio_device_get_from_dev(struct device *dev)
>  }
>  EXPORT_SYMBOL_GPL(vfio_device_get_from_dev);
>  
> +static const struct file_operations vfio_device_fops;
> +
> +int vfio_device_vma_to_pfn(struct vfio_device *device,
> +			   struct vm_area_struct *vma, unsigned long *pfn)

A comment here describing the locking conditions the caller must meet
would be a good addition.. It looks like this can only work under the
i_mmap_lock and the returned pfn can only be taken outside that lock
if it is placed in a VMA

Maybe this is not a great API then? Should it be 'populate vma' and
call io_remap_pfn_range under the op?

Jason