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Date:   Wed, 15 Nov 2017 06:58:35 -0800
From:   Matthew Wilcox <willy@infradead.org>
To:     Dave Hansen <dave.hansen@intel.com>
Cc:     Tycho Andersen <tycho@docker.com>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, kernel-hardening@lists.openwall.com,
        Marco Benatto <marco.antonio.780@gmail.com>,
        Juerg Haefliger <juerg.haefliger@canonical.com>, x86@kernel.org
Subject: Re: [PATCH v6 03/11] mm, x86: Add support for eXclusive Page Frame
 Ownership (XPFO)
Message-ID: <20171115145835.GB319@bombadil.infradead.org>
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On Tue, Nov 14, 2017 at 11:00:20PM -0800, Dave Hansen wrote:
> On 11/14/2017 07:44 PM, Matthew Wilcox wrote:
> > We don't need to kmap in order to access MOVABLE allocations.  kmap is
> > only needed for HIGHMEM allocations.  So there's nothing wrong with ext4
> > or set_bh_page().
> 
> Yeah, it's definitely not _buggy_.
> 
> Although, I do wonder what we should do about these for XPFO.  Should we
> just stick a kmap() in there and comment it?  What we really need is a
> mechanism to say "use this as a kernel page" and "stop using this as a
> kernel page".  kmap() does that... kinda.  It's not a perfect fit, but
> it's pretty close.

It'd be kind of funny if getting XPFO working better means improving
how well Linux runs on 32-bit machines with HIGHMEM.  I think there's
always going to be interest in those -- ARM developed 36 bit physmem
before biting the bullet and going to arm64.  Maybe OpenRISC will do
that next ;-)

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