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

On Wed, Feb 14, 2018 at 11:29 AM, Kees Cook <keescook@chromium.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

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