linux-kernel - Re: [PATCH v5 04/13] mm/shmem: Restrict MFD_INACCESSIBLE memory against RLIMIT

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Date:   Tue, 12 Apr 2022 11:36:36 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     David Hildenbrand <david@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Chao Peng <chao.p.peng@...ux.intel.com>,
        kvm list <kvm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        Linux API <linux-api@...r.kernel.org>, qemu-devel@...gnu.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        the arch/x86 maintainers <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, Hugh Dickins <hughd@...gle.com>,
        Jeff Layton <jlayton@...nel.org>,
        "J . Bruce Fields" <bfields@...ldses.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...nel.org>,
        Steven Price <steven.price@....com>,
        "Maciej S . Szmigiero" <mail@...iej.szmigiero.name>,
        Vlastimil Babka <vbabka@...e.cz>,
        Vishal Annapurve <vannapurve@...gle.com>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        "Nakajima, Jun" <jun.nakajima@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH v5 04/13] mm/shmem: Restrict MFD_INACCESSIBLE memory
 against RLIMIT_MEMLOCK

On Fri, Apr 08, 2022 at 08:54:02PM +0200, David Hildenbrand wrote:

> RLIMIT_MEMLOCK was the obvious candidate, but as we discovered int he
> past already with secretmem, it's not 100% that good of a fit (unmovable
> is worth than mlocked). But it gets the job done for now at least.

No, it doesn't. There are too many different interpretations how
MELOCK is supposed to work

eg VFIO accounts per-process so hostile users can just fork to go past
it.

RDMA is per-process but uses a different counter, so you can double up

iouring is per-user and users a 3rd counter, so it can triple up on
the above two

> So I'm open for alternative to limit the amount of unmovable memory we
> might allocate for user space, and then we could convert seretmem as well.

I think it has to be cgroup based considering where we are now :\

Jason