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Date: Sun, 24 Dec 2023 13:49:39 -0800 (PST)
From: David Rientjes <rientjes@google.com>
To: Pasha Tatashin <pasha.tatashin@soleen.com>
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Subject: Re: [PATCH v2 00/10] IOMMU memory observability
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On Thu, 30 Nov 2023, Pasha Tatashin wrote:

> IOMMU subsystem may contain state that is in gigabytes. Majority of that
> state is iommu page tables. Yet, there is currently, no way to observe
> how much memory is actually used by the iommu subsystem.
> 
> This patch series solves this problem by adding both observability to
> all pages that are allocated by IOMMU, and also accountability, so
> admins can limit the amount if via cgroups.
> 
> The system-wide observability is using /proc/meminfo:
> SecPageTables:    438176 kB
> 
> Contains IOMMU and KVM memory.
> 
> Per-node observability:
> /sys/devices/system/node/nodeN/meminfo
> Node N SecPageTables:    422204 kB
> 
> Contains IOMMU and KVM memory memory in the given NUMA node.
> 
> Per-node IOMMU only observability:
> /sys/devices/system/node/nodeN/vmstat
> nr_iommu_pages 105555
> 
> Contains number of pages IOMMU allocated in the given node.
> 
> Accountability: using sec_pagetables cgroup-v2 memory.stat entry.
> 
> With the change, iova_stress[1] stops as limit is reached:
> 
> # ./iova_stress
> iova space:     0T      free memory:   497G
> iova space:     1T      free memory:   495G
> iova space:     2T      free memory:   493G
> iova space:     3T      free memory:   491G
> 
> stops as limit is reached.
> 

I think this is *very* useful to provide visibility into a significant 
amount of memory that we currently cannot observe on a host.  It can help 
to uncover bugs and shed light onto a particularly large amount of memory 
that would otherwise be mysterious.

Joerg, Will, Robin, I think this series would go through the 
git://git.kernel.org/pub/scm/linux/kernel/git/joro/iommu.git tree since it 
depends on a common framework for all other IOMMU implementations to then 
use?

Any concerns about this patch series?  It would be very useful for us to 
create visibility into this memory.


Pasha: any chance of adding a selftest that can be run that will test the 
value of nr_iommu_pages?  I could imagine in the future that a bug could 
be introduced where either an allocation or free is done through 
alloc_pages() directly and its paired alloc/free function now results in a 
leak or underflow.

> This series encorporates suggestions that came from the discussion
> at LPC [2].
> ----------------------------------------------------------------------
> [1] https://github.com/soleen/iova_stress
> [2] https://lpc.events/event/17/contributions/1466
> ----------------------------------------------------------------------
> Previous versions
> v1: https://lore.kernel.org/all/20231128204938.1453583-1-pasha.tatashin@soleen.com
> ----------------------------------------------------------------------
> 
> Pasha Tatashin (10):
>   iommu/vt-d: add wrapper functions for page allocations
>   iommu/amd: use page allocation function provided by iommu-pages.h
>   iommu/io-pgtable-arm: use page allocation function provided by
>     iommu-pages.h
>   iommu/io-pgtable-dart: use page allocation function provided by
>     iommu-pages.h
>   iommu/exynos: use page allocation function provided by iommu-pages.h
>   iommu/rockchip: use page allocation function provided by iommu-pages.h
>   iommu/sun50i: use page allocation function provided by iommu-pages.h
>   iommu/tegra-smmu: use page allocation function provided by
>     iommu-pages.h
>   iommu: observability of the IOMMU allocations
>   iommu: account IOMMU allocated memory
> 
>  Documentation/admin-guide/cgroup-v2.rst |   2 +-
>  Documentation/filesystems/proc.rst      |   4 +-
>  drivers/iommu/amd/amd_iommu.h           |   8 -
>  drivers/iommu/amd/init.c                |  91 +++++-----
>  drivers/iommu/amd/io_pgtable.c          |  13 +-
>  drivers/iommu/amd/io_pgtable_v2.c       |  20 +-
>  drivers/iommu/amd/iommu.c               |  13 +-
>  drivers/iommu/exynos-iommu.c            |  14 +-
>  drivers/iommu/intel/dmar.c              |  10 +-
>  drivers/iommu/intel/iommu.c             |  47 ++---
>  drivers/iommu/intel/iommu.h             |   2 -
>  drivers/iommu/intel/irq_remapping.c     |  10 +-
>  drivers/iommu/intel/pasid.c             |  12 +-
>  drivers/iommu/intel/svm.c               |   7 +-
>  drivers/iommu/io-pgtable-arm.c          |   7 +-
>  drivers/iommu/io-pgtable-dart.c         |  37 ++--
>  drivers/iommu/iommu-pages.h             | 231 ++++++++++++++++++++++++
>  drivers/iommu/rockchip-iommu.c          |  14 +-
>  drivers/iommu/sun50i-iommu.c            |   7 +-
>  drivers/iommu/tegra-smmu.c              |  18 +-
>  include/linux/mmzone.h                  |   5 +-
>  mm/vmstat.c                             |   3 +
>  22 files changed, 390 insertions(+), 185 deletions(-)
>  create mode 100644 drivers/iommu/iommu-pages.h
> 
> -- 
> 2.43.0.rc2.451.g8631bc7472-goog
> 
> 
>