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Date: Sat, 25 May 2013 07:20:10 -0400
From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
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Subject: Re: [Qemu-devel] [PATCH 2/2] vfio: hugepage support for
	vfio_iommu_type1
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To: Alex Williamson <alex.williamson@redhat.com>
Cc: iommu@lists.linux-foundation.org, chegu_vinod@hp.com, qemu-devel@nongnu.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org

> + * Turns out AMD IOMMU has a page table bug where it won't map large pages
> + * to a region that previously mapped smaller pages.  This should be fixed
> + * soon, so this is just a temporary workaround to break mappings down into
> + * PAGE_SIZE.  Better to map smaller pages than nothing.
> + */
> +static int map_try_harder(struct vfio_iommu *iommu, dma_addr_t iova,
> +			  unsigned long pfn, long npage, int prot)
> +{
> +	long i;
> +	int ret;
> +
> +	for (i = 0; i < npage; i++, pfn++, iova += PAGE_SIZE) {
> +		ret = iommu_map(iommu->domain, iova,
> +				(phys_addr_t)pfn << PAGE_SHIFT,
> +				PAGE_SIZE, prot);
> +		if (ret)
> +			break;
> +	}
> +
> +	for (; i < npage && i > 0; i--, iova -= PAGE_SIZE)
> +		iommu_unmap(iommu->domain, iova, PAGE_SIZE);
> +
>  	return ret;
>  }

This looks to belong to a vfio-quirk file (a something else) that deals with
various IOMMU's quirks.