linux-kernel - Re: [PATCH v3 10/10] iommu: account IOMMU allocated memory

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Date: Tue, 13 Feb 2024 10:44:53 -0500
From: Pasha Tatashin <pasha.tatashin@...een.com>
To: Will Deacon <will@...nel.org>
Cc: akpm@...ux-foundation.org, alim.akhtar@...sung.com, alyssa@...enzweig.io, 
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Subject: Re: [PATCH v3 10/10] iommu: account IOMMU allocated memory

> >  SecPageTables
> > -              Memory consumed by secondary page tables, this currently
> > -              currently includes KVM mmu allocations on x86 and arm64.
> > +              Memory consumed by secondary page tables, this currently includes
> > +              KVM mmu and IOMMU allocations on x86 and arm64.

Hi Will,

> While I can see the value in this for IOMMU mappings managed by VFIO,
> doesn't this end up conflating that with the normal case of DMA domains?
> For systems that e.g. rely on an IOMMU for functional host DMA, it seems
> wrong to subject that to accounting constraints.

The accounting constraints are only applicable when GFP_KERNEL_ACCOUNT
is passed to the iommu mapping functions. We do that from the vfio,
iommufd, and vhost. Without this flag, the memory useage is reported
in /proc/meminfo as part of  SecPageTables field, but not constrained
in cgroup.

Pasha