Re: [PATCH] iommu/arm-smmu-v3: avoid over allocating for l2 stream tables

From	Will Deacon <will.deacon@arm.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] iommu/arm-smmu-v3: avoid over allocating for l2 stream tables
Date	2016-12-20 11:30 +0100
Message-ID	<sQpQd-4jH-17@gated-at.bofh.it> (permalink)
References	<sQcT0-4dL-21@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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Hi Nate,

On Mon, Dec 19, 2016 at 03:26:40PM -0500, Nate Watterson wrote:
> Currently, all l2 stream tables are being allocated with space for
> (1<<split) stes without regard to the number of sid bits the smmu
> physically supports. To avoid allocating memory for inaccessible
> stes, this patch limits the span of an l2 table to be no larger
> than the sid size of the smmu to which it belongs.
> 
> Signed-off-by: Nate Watterson <nwatters@codeaurora.org>
> ---
>  drivers/iommu/arm-smmu-v3.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)

I can't help but think you'd be better off using a linear stream table
in this scenario. If we hack the feature check for
ARM_SMMU_FEAT_2_LVL_STRTAB so that it doesn't report support for 2 level
tables if the number of sids is less than that covered by a single l2
entry, would that solve your problem?

Will

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[PATCH] iommu/arm-smmu-v3: avoid over allocating for l2 stream tables Nate Watterson <nwatters@codeaurora.org> - 2016-12-19 21:40 +0100
  Re: [PATCH] iommu/arm-smmu-v3: avoid over allocating for l2 stream  tables Will Deacon <will.deacon@arm.com> - 2016-12-20 11:30 +0100

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