linux-kernel - Re: [PATCH v6 03/11] mm, x86: Add support for eXclusive Page Frame Ownership (XPFO)

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Message-ID: <21bcc50a-f333-fb43-adef-ed501fc6b127@intel.com>
Date:   Wed, 20 Sep 2017 17:04:35 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Tycho Andersen <tycho@...ker.com>
Cc:     Yisheng Xie <xieyisheng1@...wei.com>,
        Juerg Haefliger <juerg.haefliger@...onical.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        kernel-hardening@...ts.openwall.com,
        Marco Benatto <marco.antonio.780@...il.com>, x86@...nel.org
Subject: Re: [PATCH v6 03/11] mm, x86: Add support for eXclusive Page Frame
 Ownership (XPFO)

On 09/20/2017 05:02 PM, Tycho Andersen wrote:
> ...and makes it easier to pair tlb flushes with changing the
> protections. I guess we still need the for loop, because we need to
> set/unset the xpfo bits as necessary, but I'll switch it to a single
> set_kpte(). This also implies that the xpfo bits should all be the
> same on every page in the mapping, which I think is true.

FWIW, it's a bit bonkers to keep all this duplicate xpfo metadata for
compound pages.  You could probably get away with only keeping it for
the head page.