Re: [PATCH 00/16] IOMMU memory observability

[Yosry Ahmed <yosryahmed@google.com>]

On Tue, Nov 28, 2023 at 12:49 PM Pasha Tatashin
<pasha.tatashin@soleen.com> wrote:
>
> From: Pasha Tatashin <tatashin@google.com>
>
> 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.

Does it make sense to have a KVM-only entry there as well?

In that case, if SecPageTables in /proc/meminfo is found to be
suspiciously high, it should be easy to tell which component is
contributing most usage through vmstat. I understand that users can do
the subtraction, but we wouldn't want userspace depending on that, in
case a third class of "secondary" page tables emerges that we want to
add to SecPageTables. The in-kernel implementation can do the
subtraction for now if it makes sense though.

>
> 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.
>
> 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
>
> Pasha Tatashin (16):
>   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/io-pgtable-arm-v7s: use page allocation function provided by
>     iommu-pages.h
>   iommu/dma: use page allocation function provided by iommu-pages.h
>   iommu/exynos: use page allocation function provided by iommu-pages.h
>   iommu/fsl: use page allocation function provided by iommu-pages.h
>   iommu/iommufd: 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
>   vhost-vdpa: account iommu allocations
>   vfio: account iommu allocations
>
>  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/dma-iommu.c               |   8 +-
>  drivers/iommu/exynos-iommu.c            |  14 +-
>  drivers/iommu/fsl_pamu.c                |   5 +-
>  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-v7s.c      |   9 +-
>  drivers/iommu/io-pgtable-arm.c          |   7 +-
>  drivers/iommu/io-pgtable-dart.c         |  37 ++--
>  drivers/iommu/iommu-pages.h             | 231 ++++++++++++++++++++++++
>  drivers/iommu/iommufd/iova_bitmap.c     |   6 +-
>  drivers/iommu/rockchip-iommu.c          |  14 +-
>  drivers/iommu/sun50i-iommu.c            |   7 +-
>  drivers/iommu/tegra-smmu.c              |  18 +-
>  drivers/vfio/vfio_iommu_type1.c         |   8 +-
>  drivers/vhost/vdpa.c                    |   3 +-
>  include/linux/mmzone.h                  |   5 +-
>  mm/vmstat.c                             |   3 +
>  28 files changed, 415 insertions(+), 199 deletions(-)
>  create mode 100644 drivers/iommu/iommu-pages.h
>
> --
> 2.43.0.rc2.451.g8631bc7472-goog
>
>