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	Fri, 12 Sep 2025 13:16:53 +0000
Date: Fri, 12 Sep 2025 14:16:53 +0100
From: Matthew Wilcox <willy@infradead.org>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Andreas Larsson <andreas@gaisler.com>, Arnd Bergmann <arnd@arndb.de>,
	ksummit@lists.linux.dev, linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org,
	linux-mips@vger.kernel.org, linux-mm@kvack.org, imx@lists.linux.dev,
	Christophe Leroy <christophe.leroy@csgroup.eu>,
	Richard Weinberger <richard@nod.at>,
	Lucas Stach <l.stach@pengutronix.de>,
	Linus Walleij <linus.walleij@linaro.org>,
	Geert Uytterhoeven <geert+renesas@glider.be>,
	Ankur Arora <ankur.a.arora@oracle.com>,
	David Hildenbrand <david@redhat.com>,
	Mike Rapoport <rppt@kernel.org>,
	Lorenzo Stoakes <lorenzo.stoakes@oracle.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	"Liam R. Howlett" <Liam.Howlett@oracle.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	Suren Baghdasaryan <surenb@google.com>,
	Ira Weiny <ira.weiny@intel.com>, Nishanth Menon <nm@ti.com>,
	Heiko =?iso-8859-1?Q?St=FCbner?= <heiko@sntech.de>,
	Alexander Sverdlin <alexander.sverdlin@gmail.com>,
	"Chester A. Unal" <chester.a.unal@arinc9.com>,
	Sergio Paracuellos <sergio.paracuellos@gmail.com>
Subject: Re: [TECH TOPIC] Reaching consensus on CONFIG_HIGHMEM phaseout
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References: <4ff89b72-03ff-4447-9d21-dd6a5fe1550f@app.fastmail.com>
 <5d2fec2b-8e59-417e-b9e6-12c6e27dd5f0@gaisler.com>
 <E986779F-C7AA-4940-9508-08601EE2FDD0@zytor.com>
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In-Reply-To: <E986779F-C7AA-4940-9508-08601EE2FDD0@zytor.com>

On Fri, Sep 12, 2025 at 02:58:48AM -0700, H. Peter Anvin wrote:
> On September 10, 2025 10:38:15 PM PDT, Andreas Larsson <andreas@gaisler.com> wrote:
> >We have a upcoming SoC with support for up to 16 GiB of DRAM. When that is
> >used in LEON sparc32 configuration (using 36-bit physical addressing), a
> >removed CONFIG_HIGHMEM would be a considerable limitation, even after an
> >introduction of different CONFIG_VMSPLIT_* options for sparc32.
> 
> It really sounds like a self-inflicted problem... getting your customers switched over to the RV64 side is probably the best you can do for them.


"We only support configurations above 4GB when using the RV64 core".