Re: [PATCH v1 4/4] iommu/hyperv: Add page-selective IOTLB flush support

[Jason Gunthorpe <jgg@ziepe.ca>]

On Tue, May 12, 2026 at 12:24:08AM +0800, Yu Zhang wrote:
> +static inline u16 hv_iommu_fill_iova_list(union hv_iommu_flush_va *iova_list,
> +					  unsigned long start,
> +					  unsigned long end)
> +{
> +	unsigned long start_pfn = start >> PAGE_SHIFT;
> +	unsigned long end_pfn = PAGE_ALIGN(end) >> PAGE_SHIFT;
> +	unsigned long nr_pages = end_pfn - start_pfn;
> +	u16 count = 0;
> +
> +	while (nr_pages > 0) {
> +		unsigned long flush_pages;
> +		int order;
> +		unsigned long pfn_align;
> +		unsigned long size_align;
> +
> +		if (count >= HV_IOMMU_MAX_FLUSH_VA_COUNT) {
> +			count = HV_IOMMU_FLUSH_VA_OVERFLOW;
> +			break;
> +		}
> +
> +		if (start_pfn)
> +			pfn_align = __ffs(start_pfn);
> +		else
> +			pfn_align = BITS_PER_LONG - 1;
> +
> +		size_align = __fls(nr_pages);
> +		order = min(pfn_align, size_align);
> +		iova_list[count].page_mask_shift = order;
> +		iova_list[count].page_number = start_pfn;
> +
> +		flush_pages = 1UL << order;
> +		start_pfn += flush_pages;
> +		nr_pages -= flush_pages;
> +		count++;
> +	}

This seems like a really silly hypervisor interface. Why doesn't it
just accept a normal range? Splitting it into power of two aligned
ranges is very inefficient.

Jason