linux-kernel - Re: arm64 physmap (was Re: [kernel-hardening] [PATCH 4/6] Protectable Memory)

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Message-ID: <CAGXu5jJ2XRt3RqPPXp+CN5fhT93BpCCNUHk88aSQUWS_NJ5oxw@mail.gmail.com>
Date:   Wed, 14 Feb 2018 11:35:54 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Laura Abbott <labbott@...hat.com>
Cc:     Jann Horn <jannh@...gle.com>, Igor Stoppa <igor.stoppa@...wei.com>,
        Boris Lukashev <blukashev@...pervictus.com>,
        Christopher Lameter <cl@...ux.com>,
        Matthew Wilcox <willy@...radead.org>,
        Jerome Glisse <jglisse@...hat.com>,
        Michal Hocko <mhocko@...nel.org>,
        Christoph Hellwig <hch@...radead.org>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: arm64 physmap (was Re: [kernel-hardening] [PATCH 4/6] Protectable Memory)

On Wed, Feb 14, 2018 at 11:29 AM, Kees Cook <keescook@...omium.org> wrote:
> Why does using finer granularity on the physmap degrade performance? I
> assume TLB pressure, but what is heavily using that area? (I must not
> be understanding what physmap actually gets used for -- I thought it
> was just a convenience to have a 1:1 virt/phys map for some lookups?)

Jann has sorted me out: it's that physmap isn't an _alias_ for the
buddy allocator memory areas; it's used directly.

-Kees

-- 
Kees Cook
Pixel Security