linux-kernel - Re: [PATCH 00/16] IOMMU memory observability

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]

Message-ID: <CAJD7tkbxhK7XFcf7h+XE2poNuOsFBQFrxZyeFr=9DoEG_acssA@mail.gmail.com>
Date:   Tue, 28 Nov 2023 16:30:27 -0800
From:   Yosry Ahmed <yosryahmed@...gle.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     Pasha Tatashin <pasha.tatashin@...een.com>,
        akpm@...ux-foundation.org, alex.williamson@...hat.com,
        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, jasowang@...hat.com,
        jernej.skrabec@...il.com, jonathanh@...dia.com, joro@...tes.org,
        kevin.tian@...el.com, krzysztof.kozlowski@...aro.org,
        kvm@...r.kernel.org, linux-arm-kernel@...ts.infradead.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, mst@...hat.com,
        m.szyprowski@...sung.com, netdev@...r.kernel.org,
        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,
        virtualization@...ts.linux.dev, wens@...e.org, will@...nel.org,
        yu-cheng.yu@...el.com
Subject: Re: [PATCH 00/16] IOMMU memory observability

On Tue, Nov 28, 2023 at 4:28 PM Jason Gunthorpe <jgg@...pe.ca> wrote:
>
> On Tue, Nov 28, 2023 at 04:25:03PM -0800, Yosry Ahmed wrote:
>
> > > > Right, but as I mention above, if userspace starts depending on this
> > > > equation, we won't be able to add any more classes of "secondary" page
> > > > tables to SecPageTables. I'd like to avoid that if possible. We can do
> > > > the subtraction in the kernel.
> > >
> > > What Sean had suggested was that SecPageTables was always intended to
> > > account all the non-primary mmu memory used by page tables. If this is
> > > the case we shouldn't be trying to break it apart into finer
> > > counters. These are big picture counters, not detailed allocation by
> > > owner counters.
> >
> > Right, I agree with that, but if SecPageTables includes page tables
> > from multiple sources, and it is observed to be suspiciously high, the
> > logical next step is to try to find the culprit, right?
>
> You can make that case already, if it is high wouldn't you want to
> find the exact VMM process that was making it high?
>
> It is a sign of fire, not a detailed debug tool.

Fair enough. We can always add separate counters later if needed,
potentially under KVM stats to get more fine-grained details as you
mentioned.

I am only worried about users subtracting the iommu-only counter to
get a KVM counter. We should at least document that  SecPageTables may
be expanded to include other sources later to avoid that.

>
> Jason