Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 6a3ea3c6 authored by Liam Mark's avatar Liam Mark Committed by Todd Kjos
Browse files

FROMLIST: iommu/iova: Support limiting IOVA alignment 

When the IOVA framework applies IOVA alignment it aligns all
IOVAs to the smallest PAGE_SIZE order which is greater than or
equal to the requested IOVA size.

We support use cases that requires large buffers (> 64 MB in
size) to be allocated and mapped in their stage 1 page tables.
However, with this alignment scheme we find ourselves running
out of IOVA space for 32 bit devices, so we are proposing this
config, along the similar vein as CONFIG_CMA_ALIGNMENT for CMA
allocations.

Add CONFIG_IOMMU_LIMIT_IOVA_ALIGNMENT to limit the alignment of
IOVAs to some desired PAGE_SIZE order, specified by
CONFIG_IOMMU_IOVA_ALIGNMENT. This helps reduce the impact of
fragmentation caused by the current IOVA alignment scheme, and
gives better IOVA space utilization.

Bug: 148141615
Link: https://lore.kernel.org/lkml/alpine.DEB.2.10.2002141223510.27047@lmark-linux.qualcomm.com/


Change-Id: I511ac685d5855e1b9feb5025e025ebbebee7f40d
Signed-off-by: default avatarLiam Mark <lmark@codeaurora.org>
parent 5e25537a

drivers/iommu/Kconfig

+30 −0
Original line number Diff line number Diff line
@@ -7,6 +7,36 @@ config IOMMU_IOVA 
config IOMMU_API

	bool



if IOMMU_IOVA



config IOMMU_LIMIT_IOVA_ALIGNMENT

	bool "Limit IOVA alignment"

	help

	  When the IOVA framework applies IOVA alignment it aligns all

	  IOVAs to the smallest PAGE_SIZE order which is greater than or

	  equal to the requested IOVA size. This works fine for sizes up

	  to several MiB, but for larger sizes it results in address

	  space wastage and fragmentation. For example drivers with a 4

	  GiB IOVA space might run out of IOVA space when allocating

	  buffers great than 64 MiB.



	  Enable this option to impose a limit on the alignment of IOVAs.



	  If unsure, say N.



config IOMMU_IOVA_ALIGNMENT

	int "Maximum PAGE_SIZE order of alignment for IOVAs"

	depends on IOMMU_LIMIT_IOVA_ALIGNMENT

	range 4 9

	default 9

	help

	  With this parameter you can specify the maximum PAGE_SIZE order for

	  IOVAs. Larger IOVAs will be aligned only to this specified order.

	  The order is expressed a power of two multiplied by the PAGE_SIZE.



	  If unsure, leave the default value "9".

endif



menuconfig IOMMU_SUPPORT

	bool "IOMMU Hardware Support"

	depends on MMU

drivers/iommu/iova.c

+20 −2
Original line number Diff line number Diff line
@@ -178,6 +178,24 @@ iova_insert_rbtree(struct rb_root *root, struct iova *iova, 
	rb_insert_color(&iova->node, root);

}



#ifdef CONFIG_IOMMU_LIMIT_IOVA_ALIGNMENT

static unsigned long limit_align_shift(struct iova_domain *iovad,

				       unsigned long shift)

{

	unsigned long max_align_shift;



	max_align_shift = CONFIG_IOMMU_IOVA_ALIGNMENT + PAGE_SHIFT

		- iova_shift(iovad);

	return min_t(unsigned long, max_align_shift, shift);

}

#else

static unsigned long limit_align_shift(struct iova_domain *iovad,

				       unsigned long shift)

{

	return shift;

}

#endif



static int __alloc_and_insert_iova_range(struct iova_domain *iovad,

		unsigned long size, unsigned long limit_pfn,

			struct iova *new, bool size_aligned)
@@ -189,7 +207,7 @@ static int __alloc_and_insert_iova_range(struct iova_domain *iovad, 
	unsigned long align_mask = ~0UL;



	if (size_aligned)

		align_mask <<= fls_long(size - 1);

		align_mask <<= limit_align_shift(iovad, fls_long(size - 1));



	/* Walk the tree backwards */

	spin_lock_irqsave(&iovad->iova_rbtree_lock, flags);
@@ -242,7 +260,7 @@ static int __alloc_and_insert_iova_best_fit(struct iova_domain *iovad, 
	unsigned long gap, candidate_gap = ~0UL;



	if (size_aligned)

		align_mask <<= limit_align(iovad, fls_long(size - 1));

		align_mask <<= limit_align_shift(iovad, fls_long(size - 1));



	/* Walk the tree backwards */

	spin_lock_irqsave(&iovad->iova_rbtree_lock, flags);