linux-kernel - Re: [PATCH v16 07/11] secretmem: use PMD-size pages to amortize direct map fragmentation

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Date:   Thu, 28 Jan 2021 13:28:10 +0000 (UTC)
From:   Christoph Lameter <cl@...ux.com>
To:     Michal Hocko <mhocko@...e.com>
cc:     Mike Rapoport <rppt@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andy Lutomirski <luto@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Elena Reshetova <elena.reshetova@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        James Bottomley <jejb@...ux.ibm.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Matthew Wilcox <willy@...radead.org>,
        Mark Rutland <mark.rutland@....com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Roman Gushchin <guro@...com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Shuah Khan <shuah@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tycho Andersen <tycho@...ho.ws>, Will Deacon <will@...nel.org>,
        linux-api@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-nvdimm@...ts.01.org, linux-riscv@...ts.infradead.org,
        x86@...nel.org, Hagen Paul Pfeifer <hagen@...u.net>,
        Palmer Dabbelt <palmerdabbelt@...gle.com>
Subject: Re: [PATCH v16 07/11] secretmem: use PMD-size pages to amortize
 direct map fragmentation

On Thu, 28 Jan 2021, Michal Hocko wrote:

> > So, if I understand your concerns correct this implementation has two
> > issues:
> > 1) allocation failure at page fault that causes unrecoverable OOM and
> > 2) a possibility for an unprivileged user to deplete secretmem pool and
> > cause (1) to others
> >
> > I'm not really familiar with OOM internals, but when I simulated an
> > allocation failure in my testing only the allocating process and it's
> > parent were OOM-killed and then the system continued normally.
>
> If you kill the allocating process then yes, it would work, but your
> process might be the very last to be selected.

OOMs are different if you have a "constrained allocation". In that case it
is the fault of the process who wanted memory with certain conditions.
That memory is not available. General memory is available though. In that
case the allocating process is killed.