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Date: Sun, 18 Feb 2024 14:07:17 +0200
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Subject: Re: [PATCH v18 2/3] vfio/pci: rename and export range_intersect_range
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To: <ankita@nvidia.com>, <jgg@nvidia.com>, <alex.williamson@redhat.com>,
	<shameerali.kolothum.thodi@huawei.com>, <kevin.tian@intel.com>,
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CC: <aniketa@nvidia.com>, <cjia@nvidia.com>, <kwankhede@nvidia.com>,
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References: <20240216030128.29154-1-ankita@nvidia.com>
 <20240216030128.29154-3-ankita@nvidia.com>
From: Yishai Hadas <yishaih@nvidia.com>
In-Reply-To: <20240216030128.29154-3-ankita@nvidia.com>
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On 16/02/2024 5:01, ankita@nvidia.com wrote:
> From: Ankit Agrawal <ankita@nvidia.com>
> 
> range_intersect_range determines an overlap between two ranges. If an
> overlap, the helper 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.
> 
> Make this a vfio_pci_core function, rename and export as GPL. Also
> update references in virtio driver.
> 
> Reviewed-by: Kevin Tian <kevin.tian@intel.com>
> Signed-off-by: Ankit Agrawal <ankita@nvidia.com>
> ---
>   drivers/vfio/pci/vfio_pci_config.c | 42 +++++++++++++++++
>   drivers/vfio/pci/virtio/main.c     | 72 +++++++++++-------------------
>   include/linux/vfio_pci_core.h      |  5 +++
>   3 files changed, 73 insertions(+), 46 deletions(-)
> 
> diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c
> index 672a1804af6a..e2e6173a3375 100644
> --- a/drivers/vfio/pci/vfio_pci_config.c
> +++ b/drivers/vfio/pci/vfio_pci_config.c
> @@ -1966,3 +1966,45 @@ ssize_t vfio_pci_config_rw(struct vfio_pci_core_device *vdev, char __user *buf,
>   
>   	return done;
>   }
> +
> +/**
> + * vfio_pci_core_range_intersect_range() - Determine overlap between a buffer
> + *					   and register offset ranges.
> + * @buf_start:		start offset of the buffer
> + * @buf_cnt:		number of buffer bytes.

You could drop the '.' at the end to be consistent with the other.

> + * @reg_start:		start register offset
> + * @reg_cnt:		number of register bytes
> + * @buf_offset:	start offset of overlap in the buffer
> + * @intersect_count:	number of overlapping bytes
> + * @register_offset:	start offset of overlap in register
> + *
> + * Returns: true if there is overlap, false if not.
> + * The overlap start and size is returned through function args.
> + */
> +bool vfio_pci_core_range_intersect_range(loff_t buf_start, size_t buf_cnt,
> +					 loff_t reg_start, size_t reg_cnt,
> +					 loff_t *buf_offset,
> +					 size_t *intersect_count,
> +					 size_t *register_offset)
> +{
> +	if (buf_start <= reg_start &&
> +	    buf_start + buf_cnt > reg_start) {
> +		*buf_offset = reg_start - buf_start;
> +		*intersect_count = min_t(size_t, reg_cnt,
> +					 buf_start + buf_cnt - reg_start);
> +		*register_offset = 0;
> +		return true;
> +	}
> +
> +	if (buf_start > reg_start &&
> +	    buf_start < reg_start + reg_cnt) {
> +		*buf_offset = 0;
> +		*intersect_count = min_t(size_t, buf_cnt,
> +					 reg_start + reg_cnt - buf_start);
> +		*register_offset = buf_start - reg_start;
> +		return true;
> +	}
> +
> +	return false;
> +}
> +EXPORT_SYMBOL_GPL(vfio_pci_core_range_intersect_range);
> diff --git a/drivers/vfio/pci/virtio/main.c b/drivers/vfio/pci/virtio/main.c
> index d5af683837d3..b5d3a8c5bbc9 100644
> --- a/drivers/vfio/pci/virtio/main.c
> +++ b/drivers/vfio/pci/virtio/main.c
> @@ -132,33 +132,6 @@ virtiovf_pci_bar0_rw(struct virtiovf_pci_core_device *virtvdev,
>   	return ret ? ret : count;
>   }
>   
> -static 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;
> -}
> -
>   static ssize_t virtiovf_pci_read_config(struct vfio_device *core_vdev,
>   					char __user *buf, size_t count,
>   					loff_t *ppos)
> @@ -178,16 +151,18 @@ static ssize_t virtiovf_pci_read_config(struct vfio_device *core_vdev,
>   	if (ret < 0)
>   		return ret;
>   
> -	if (range_intersect_range(pos, count, PCI_DEVICE_ID, sizeof(val16),
> -				  &copy_offset, &copy_count, &register_offset)) {
> +	if (vfio_pci_core_range_intersect_range(pos, count, PCI_DEVICE_ID,
> +						sizeof(val16), &copy_offset,
> +						&copy_count, &register_offset)) {
>   		val16 = cpu_to_le16(VIRTIO_TRANS_ID_NET);
>   		if (copy_to_user(buf + copy_offset, (void *)&val16 + register_offset, copy_count))
>   			return -EFAULT;
>   	}
>   
>   	if ((le16_to_cpu(virtvdev->pci_cmd) & PCI_COMMAND_IO) &&
> -	    range_intersect_range(pos, count, PCI_COMMAND, sizeof(val16),
> -				  &copy_offset, &copy_count, &register_offset)) {
> +	    vfio_pci_core_range_intersect_range(pos, count, PCI_COMMAND,
> +						sizeof(val16), &copy_offset,
> +						&copy_count, &register_offset)) {
>   		if (copy_from_user((void *)&val16 + register_offset, buf + copy_offset,
>   				   copy_count))
>   			return -EFAULT;
> @@ -197,16 +172,18 @@ static ssize_t virtiovf_pci_read_config(struct vfio_device *core_vdev,
>   			return -EFAULT;
>   	}
>   
> -	if (range_intersect_range(pos, count, PCI_REVISION_ID, sizeof(val8),
> -				  &copy_offset, &copy_count, &register_offset)) {
> +	if (vfio_pci_core_range_intersect_range(pos, count, PCI_REVISION_ID,
> +						sizeof(val8), &copy_offset,
> +						&copy_count, &register_offset)) {
>   		/* Transional needs to have revision 0 */
>   		val8 = 0;
>   		if (copy_to_user(buf + copy_offset, &val8, copy_count))
>   			return -EFAULT;
>   	}
>   
> -	if (range_intersect_range(pos, count, PCI_BASE_ADDRESS_0, sizeof(val32),
> -				  &copy_offset, &copy_count, &register_offset)) {
> +	if (vfio_pci_core_range_intersect_range(pos, count, PCI_BASE_ADDRESS_0,
> +						sizeof(val32), &copy_offset,
> +						&copy_count, &register_offset)) {
>   		u32 bar_mask = ~(virtvdev->bar0_virtual_buf_size - 1);
>   		u32 pci_base_addr_0 = le32_to_cpu(virtvdev->pci_base_addr_0);
>   
> @@ -215,8 +192,9 @@ static ssize_t virtiovf_pci_read_config(struct vfio_device *core_vdev,
>   			return -EFAULT;
>   	}
>   
> -	if (range_intersect_range(pos, count, PCI_SUBSYSTEM_ID, sizeof(val16),
> -				  &copy_offset, &copy_count, &register_offset)) {
> +	if (vfio_pci_core_range_intersect_range(pos, count, PCI_SUBSYSTEM_ID,
> +						sizeof(val16), &copy_offset,
> +						&copy_count, &register_offset)) {
>   		/*
>   		 * Transitional devices use the PCI subsystem device id as
>   		 * virtio device id, same as legacy driver always did.
> @@ -227,8 +205,9 @@ static ssize_t virtiovf_pci_read_config(struct vfio_device *core_vdev,
>   			return -EFAULT;
>   	}
>   
> -	if (range_intersect_range(pos, count, PCI_SUBSYSTEM_VENDOR_ID, sizeof(val16),
> -				  &copy_offset, &copy_count, &register_offset)) {
> +	if (vfio_pci_core_range_intersect_range(pos, count, PCI_SUBSYSTEM_VENDOR_ID,
> +						sizeof(val16), &copy_offset,
> +						&copy_count, &register_offset)) {
>   		val16 = cpu_to_le16(PCI_VENDOR_ID_REDHAT_QUMRANET);
>   		if (copy_to_user(buf + copy_offset, (void *)&val16 + register_offset,
>   				 copy_count))
> @@ -270,19 +249,20 @@ static ssize_t virtiovf_pci_write_config(struct vfio_device *core_vdev,
>   	loff_t copy_offset;
>   	size_t copy_count;
>   
> -	if (range_intersect_range(pos, count, PCI_COMMAND, sizeof(virtvdev->pci_cmd),
> -				  &copy_offset, &copy_count,
> -				  &register_offset)) {
> +	if (vfio_pci_core_range_intersect_range(pos, count, PCI_COMMAND,
> +						sizeof(virtvdev->pci_cmd),
> +						&copy_offset, &copy_count,
> +						&register_offset)) {
>   		if (copy_from_user((void *)&virtvdev->pci_cmd + register_offset,
>   				   buf + copy_offset,
>   				   copy_count))
>   			return -EFAULT;
>   	}
>   
> -	if (range_intersect_range(pos, count, PCI_BASE_ADDRESS_0,
> -				  sizeof(virtvdev->pci_base_addr_0),
> -				  &copy_offset, &copy_count,
> -				  &register_offset)) {
> +	if (vfio_pci_core_range_intersect_range(pos, count, PCI_BASE_ADDRESS_0,
> +						sizeof(virtvdev->pci_base_addr_0),
> +						&copy_offset, &copy_count,
> +						&register_offset)) {
>   		if (copy_from_user((void *)&virtvdev->pci_base_addr_0 + register_offset,
>   				   buf + copy_offset,
>   				   copy_count))
> diff --git a/include/linux/vfio_pci_core.h b/include/linux/vfio_pci_core.h
> index cf9480a31f3e..a2c8b8bba711 100644
> --- a/include/linux/vfio_pci_core.h
> +++ b/include/linux/vfio_pci_core.h
> @@ -134,6 +134,11 @@ 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 vfio_pci_core_range_intersect_range(loff_t buf_start, size_t buf_cnt,
> +					 loff_t reg_start, size_t reg_cnt,
> +					 loff_t *buf_offset,
> +					 size_t *intersect_count,
> +					 size_t *register_offset);
>   #define VFIO_IOWRITE_DECLATION(size) \
>   int vfio_pci_core_iowrite##size(struct vfio_pci_core_device *vdev,	\
>   			bool test_mem, u##size val, void __iomem *io);

Reviewed-by: Yishai Hadas <yishaih@nvidia.com>