On 18/08/2021 13:06, Xie Yongji wrote:

+
+static dma_addr_t
+vduse_domain_alloc_iova(struct iova_domain *iovad,
+			unsigned long size, unsigned long limit)
+{
+	unsigned long shift = iova_shift(iovad);
+	unsigned long iova_len = iova_align(iovad, size) >> shift;
+	unsigned long iova_pfn;
+
+	/*
+	 * Freeing non-power-of-two-sized allocations back into the IOVA caches
+	 * will come back to bite us badly, so we have to waste a bit of space
+	 * rounding up anything cacheable to make sure that can't happen. The
+	 * order of the unadjusted size will still match upon freeing.
+	 */
+	if (iova_len < (1 << (IOVA_RANGE_CACHE_MAX_SIZE - 1)))
+		iova_len = roundup_pow_of_two(iova_len);

Whether it's proper to use this "fast" API or not here, this seems to be 
copied verbatim from dma-iommu.c, which tells me that something should 
be factored out.

Indeed, this rounding up seems a requirement of the rcache, so not sure 
why this is not done there.

+	iova_pfn = alloc_iova_fast(iovad, iova_len, limit >> shift, true);

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