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Commit 8f6429c7 authored by Robin Murphy's avatar Robin Murphy Committed by David Woodhouse
Browse files

iommu/iova: Avoid over-allocating when size-aligned 



Currently, allocating a size-aligned IOVA region quietly adjusts the
actual allocation size in the process, returning a rounded-up
power-of-two-sized allocation. This results in mismatched behaviour in
the IOMMU driver if the original size was not a power of two, where the
original size is mapped, but the rounded-up IOVA size is unmapped.

Whilst some IOMMUs will happily unmap already-unmapped pages, others
consider this an error, so fix it by computing the necessary alignment
padding without altering the actual allocation size. Also clean up by
making pad_size unsigned, since its callers always pass unsigned values
and negative padding makes little sense here anyway.

Signed-off-by: default avatarRobin Murphy <robin.murphy@arm.com>
Signed-off-by: default avatarDavid Woodhouse <David.Woodhouse@intel.com>
parent 52721d9d

drivers/iommu/intel-iommu.c

+2 −0
Original line number Diff line number Diff line
@@ -3233,6 +3233,8 @@ static struct iova *intel_alloc_iova(struct device *dev, 


	/* Restrict dma_mask to the width that the iommu can handle */

	dma_mask = min_t(uint64_t, DOMAIN_MAX_ADDR(domain->gaw), dma_mask);

	/* Ensure we reserve the whole size-aligned region */

	nrpages = __roundup_pow_of_two(nrpages);



	if (!dmar_forcedac && dma_mask > DMA_BIT_MASK(32)) {

		/*

drivers/iommu/iova.c

+6 −17
Original line number Diff line number Diff line
@@ -120,19 +120,14 @@ __cached_rbnode_delete_update(struct iova_domain *iovad, struct iova *free) 
	}

}



/* Computes the padding size required, to make the

 * the start address naturally aligned on its size

/*

 * Computes the padding size required, to make the start address

 * naturally aligned on the power-of-two order of its size

 */

static int

iova_get_pad_size(int size, unsigned int limit_pfn)

static unsigned int

iova_get_pad_size(unsigned int size, unsigned int limit_pfn)

{

	unsigned int pad_size = 0;

	unsigned int order = ilog2(size);



	if (order)

		pad_size = (limit_pfn + 1) % (1 << order);



	return pad_size;

	return (limit_pfn + 1 - size) & (__roundup_pow_of_two(size) - 1);

}



static int __alloc_and_insert_iova_range(struct iova_domain *iovad,
@@ -265,12 +260,6 @@ alloc_iova(struct iova_domain *iovad, unsigned long size, 
	if (!new_iova)

		return NULL;



	/* If size aligned is set then round the size to

	 * to next power of two.

	 */

	if (size_aligned)

		size = __roundup_pow_of_two(size);



	ret = __alloc_and_insert_iova_range(iovad, size, limit_pfn,

			new_iova, size_aligned);