Re: [PATCH v2 00/10] IOMMU memory observability

David Rientjes
2023-12-24T21:49:52Z

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