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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date: Fri, 16 Feb 2024 17:57:52 +0000
From: Will Deacon <will@...nel.org>
To: Pasha Tatashin <pasha.tatashin@...een.com>
Cc: akpm@...ux-foundation.org, alim.akhtar@...sung.com,
	alyssa@...enzweig.io, asahi@...ts.linux.dev,
	baolu.lu@...ux.intel.com, bhelgaas@...gle.com,
	cgroups@...r.kernel.org, corbet@....net, david@...hat.com,
	dwmw2@...radead.org, hannes@...xchg.org, heiko@...ech.de,
	iommu@...ts.linux.dev, jernej.skrabec@...il.com,
	jonathanh@...dia.com, joro@...tes.org,
	krzysztof.kozlowski@...aro.org, linux-doc@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-rockchip@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org, linux-sunxi@...ts.linux.dev,
	linux-tegra@...r.kernel.org, lizefan.x@...edance.com,
	marcan@...can.st, mhiramat@...nel.org, m.szyprowski@...sung.com,
	paulmck@...nel.org, rdunlap@...radead.org, robin.murphy@....com,
	samuel@...lland.org, suravee.suthikulpanit@....com,
	sven@...npeter.dev, thierry.reding@...il.com, tj@...nel.org,
	tomas.mudrunka@...il.com, vdumpa@...dia.com, wens@...e.org,
	yu-cheng.yu@...el.com, rientjes@...gle.com
Subject: Re: [PATCH v3 10/10] iommu: account IOMMU allocated memory

On Tue, Feb 13, 2024 at 10:44:53AM -0500, Pasha Tatashin wrote:
> > >  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.

Thanks, Pasha, that explanation makes sense. I still find it bizarre to
include IOMMU allocations from the DMA API in SecPageTables though, and
I worry that it will confuse people who are using that metric as a way
to get a feeling for how much memory is being used by KVM's secondary
page-tables. As an extreme example, having a non-zero SecPageTables count
without KVM even compiled in is pretty bizarre.

Will