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[2a02:3100:ae93:f301:cdd9:d5ea:80d:9131]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-47f85bd850asm26780306f8f.15.2026.07.24.15.06.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 24 Jul 2026 15:06:45 -0700 (PDT) Date: Sat, 25 Jul 2026 00:06:43 +0200 From: Karl Mehltretter To: Arnd Bergmann Cc: linux-arm-kernel@lists.infradead.org, Russell King , Kevin Cernekee , Gregory Fong Subject: Re: [PATCH v2] ARM: set !LPAE MAX_PHYSMEM_BITS to 32 and remove IO_36 Message-ID: References: <20260724174748.65958-1-kmehltretter@gmail.com> <0d6dbd8f-c5c5-49d2-b36e-3cdd404eb55b@app.fastmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0d6dbd8f-c5c5-49d2-b36e-3cdd404eb55b@app.fastmail.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260724_150648_047161_A128D678 X-CRM114-Status: GOOD ( 13.14 ) 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 Fri, Jul 24, 2026 at 08:31:35PM +0100, Arnd Bergmann wrote: > > I'm not sure why you remove remap_area_supersections() but keep > create_36bit_mapping(). I would just remove that as well. Sorry, my earlier explanation was confusing. create_36bit_mapping() is not totally unreachable after this patch. The ARM EFI path can reach it through: efi_create_mapping() -> create_mapping_late() -> create_36bit_mapping() I verified this with a modified EDK2 build under QEMU that advertised an aligned, write-back EFI runtime memory descriptor above 4 GiB. The kernel successfully created the mapping and enabled EFI runtime services. Admittedly, this is a synthetic configuration. Stock ARM32 EDK2 restricts allocations to below 4 GiB, and I believe the AArch32 UEFI specification requires RAM in the UEFI memory map to be identity-mapped during boot services. The test setup is therefore probably not a conforming real-world firmware configuration. Maybe you want to keep create_36bit_mapping() because of that? Alternatively, if this should be considered unsupported, I can remove it in v3 as you suggested. If create_36bit_mapping() remains, I will update the commit message to clarify that the patch removes 36-bit I/O mappings, while retaining the generic supersection mapping path for domain-0 memory mappings. Thanks, Karl