Re: [PATCH v11 10/12] vduse: Implement an MMU-based software IOTLB

[John Garry]

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);