Re: [PATCH v16 2/3] vfio/pci: implement range_intesect_range to determine range overlap

[Alex Williamson <alex.williamson@redhat.com>]

On Mon, 15 Jan 2024 21:15:15 +0000
<ankita@nvidia.com> wrote:

> From: Ankit Agrawal <ankita@nvidia.com>
> 
> Add a helper function to determine an overlap between two ranges.
> If an overlap, the function returns the overlapping offset and size.
> 
> The VFIO PCI variant driver emulates the PCI config space BAR offset
> registers. These offset may be accessed for read/write with a variety
> of lengths including sub-word sizes from sub-word offsets. The driver
> makes use of this helper function to read/write the targeted part of
> the emulated register.
> 
> This is replicated from Yishai's work in
> https://lore.kernel.org/all/20231207102820.74820-10-yishaih@nvidia.com

The virtio-vfio-net changes have been accepted, so this will need to be
rebased on the vfio next branch or v6.8-rc1 when Linus comes back
online to process the pull request.  The revised patch should
consolidate so that virtio-vfio-pci also uses the new shared function.

As noted by Rahul, the name should be updated to align with the
vfio-pci-core namespace.  Kerneldoc would also be a nice addition since
this is a somewhat complicated helper.  Thanks,

Alex

> Signed-off-by: Ankit Agrawal <ankita@nvidia.com>
> Tested-by: Ankit Agrawal <ankita@nvidia.com>
> ---
>  drivers/vfio/pci/vfio_pci_config.c | 28 ++++++++++++++++++++++++++++
>  include/linux/vfio_pci_core.h      |  6 ++++++
>  2 files changed, 34 insertions(+)
> 
> diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c
> index 7e2e62ab0869..b77c96fbc4b2 100644
> --- a/drivers/vfio/pci/vfio_pci_config.c
> +++ b/drivers/vfio/pci/vfio_pci_config.c
> @@ -1966,3 +1966,31 @@ ssize_t vfio_pci_config_rw(struct vfio_pci_core_device *vdev, char __user *buf,
>  
>  	return done;
>  }
> +
> +bool range_intersect_range(loff_t range1_start, size_t count1,
> +			   loff_t range2_start, size_t count2,
> +			   loff_t *start_offset,
> +			   size_t *intersect_count,
> +			   size_t *register_offset)
> +{
> +	if (range1_start <= range2_start &&
> +	    range1_start + count1 > range2_start) {
> +		*start_offset = range2_start - range1_start;
> +		*intersect_count = min_t(size_t, count2,
> +					 range1_start + count1 - range2_start);
> +		*register_offset = 0;
> +		return true;
> +	}
> +
> +	if (range1_start > range2_start &&
> +	    range1_start < range2_start + count2) {
> +		*start_offset = 0;
> +		*intersect_count = min_t(size_t, count1,
> +					 range2_start + count2 - range1_start);
> +		*register_offset = range1_start - range2_start;
> +		return true;
> +	}
> +
> +	return false;
> +}
> +EXPORT_SYMBOL_GPL(range_intersect_range);
> diff --git a/include/linux/vfio_pci_core.h b/include/linux/vfio_pci_core.h
> index d478e6f1be02..8a11047ac6c9 100644
> --- a/include/linux/vfio_pci_core.h
> +++ b/include/linux/vfio_pci_core.h
> @@ -133,4 +133,10 @@ ssize_t vfio_pci_core_do_io_rw(struct vfio_pci_core_device *vdev, bool test_mem,
>  			       void __iomem *io, char __user *buf,
>  			       loff_t off, size_t count, size_t x_start,
>  			       size_t x_end, bool iswrite);
> +
> +bool range_intersect_range(loff_t range1_start, size_t count1,
> +			   loff_t range2_start, size_t count2,
> +			   loff_t *start_offset,
> +			   size_t *intersect_count,
> +			   size_t *register_offset);
>  #endif /* VFIO_PCI_CORE_H */