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Wed, 10 Sep 2025 11:14:17 -0400 (EDT) X-Mailer: MessagingEngine.com Webmail Interface MIME-Version: 1.0 X-ThreadId: AmcCJOTBQ5ho Date: Wed, 10 Sep 2025 17:13:57 +0200 From: "Arnd Bergmann" To: "Matthew Wilcox" , "Linus Walleij" Cc: 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" , "Richard Weinberger" , "Lucas Stach" , "Geert Uytterhoeven" , "Ankur Arora" , "David Hildenbrand" , "Mike Rapoport" , "Lorenzo Stoakes" , "Andrew Morton" , "Liam R. Howlett" , "Vlastimil Babka" , "Suren Baghdasaryan" , "Ira Weiny" , "Nishanth Menon" , =?UTF-8?Q?Heiko_St=C3=BCbner?= , "Alexander Sverdlin" , "Chester A. Unal" , "Sergio Paracuellos" , "Andreas Larsson" Message-Id: <55cbc329-4b14-4f62-90bb-1e1007cc1152@app.fastmail.com> In-Reply-To: References: <4ff89b72-03ff-4447-9d21-dd6a5fe1550f@app.fastmail.com> Subject: Re: [TECH TOPIC] Reaching consensus on CONFIG_HIGHMEM phaseout Content-Type: text/plain Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250910_081422_022362_BB021AE9 X-CRM114-Status: GOOD ( 11.84 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Sep 10, 2025, at 16:04, Matthew Wilcox wrote: > On Wed, Sep 10, 2025 at 03:10:05PM +0200, Linus Walleij wrote: >> >> This in practice means the area 0xf1000000-0xffffffff >> which also includes the high exception vectors that must for >> natural reasons also be kept in the mapping. >> What we have mapped today (all of the time) is >> 0xc0000000-0xffffffff. >> >> A minimal 256 MB mapping from 0xf0000000-0xffffffff >> should be able to cover this. > > Can I ask where the MMIO (PCI?) window lives? That 256MB area is shared by anything the kernel can access directly, other than the linear map: vmlinux, modules, vmalloc, ioremap, vmap-stack, etc. This is mostly unchanged from the tradtitional layout on arm32 that has the same ~256MB limitation, though it does get a little tighter because .text/.data is now also mapped into this space instead of executed from the linear map. ARnd