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Wed, 1 Feb 2023 03:06:00 -0500 (EST) X-Mailer: MessagingEngine.com Webmail Interface User-Agent: Cyrus-JMAP/3.9.0-alpha0-107-g82c3c54364-fm-20230131.002-g82c3c543 Mime-Version: 1.0 Message-Id: In-Reply-To: <11BE997B-93C7-4D38-99BF-FD025A1FB945@jrtc27.com> References: <11BE997B-93C7-4D38-99BF-FD025A1FB945@jrtc27.com> Date: Wed, 01 Feb 2023 09:05:41 +0100 From: "Arnd Bergmann" To: "Jessica Clarke" , "Christoph Hellwig" Cc: "Matthew Wilcox" , Prabhakar , Linux-MM , linux-riscv , Linux-Renesas , "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , "Palmer Dabbelt" , "Rob Herring" , "Krzysztof Kozlowski" , "Geert Uytterhoeven" , "Fabrizio Castro" , "Biju Das" , "Chris Paterson" Subject: Re: [QUERY]: Block region to mmap Content-Type: text/plain X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: 79rn1wtni551npzzwfih4up1jnfonwtj X-Rspamd-Queue-Id: 108E3C0007 X-HE-Tag: 1675238761-238842 X-HE-Meta: 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 mtg7nySL 450h0hAlP6fRazUtpOtRU4IHzgFsSA+lOLAfZKlAJkSqUOsDo4ALC2XmY3EheU3tCbqx37Yj07MZfy8aNY/784HuuXER8GwAYuCN5Io2MI9ExfDx+k6VW/oTqpabK8BMIXA2r3VDZqD/dzGu9qCgNpQMdNPZ9PJYYfculdGMqUh7Q5EY1Sl2hWwCEp9F2L1z3SkV+TDH3ctMpIrgJfJFqhWhTeO9Kf503yAZj3FGMVPxg6m7njQnz1t+ssfhCrFot+t6O4lDVlmbLKn2rES1t2uhE9A== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Feb 1, 2023, at 08:05, Jessica Clarke wrote: > On 1 Feb 2023, at 06:31, Christoph Hellwig wrote: >> On Mon, Jan 30, 2023 at 03:24:40PM +0000, Matthew Wilcox wrote: >> >>> Before we go too deeply into it, how much would it cost to buy all of >>> these parts and feed them into a shredder? I'm not entirely joking; >>> if it's less than the software engineering time it'd take to develop >>> and support this feature, we should do it. >> >> The above suggests this is in no way an actual hardware problem, but the >> stupid decision is done in the M-Mode firmware. I think it is very >> reasonable to simply not support the devices in Linux until the firmware >> is fixed. > > No, it really is a hardware spec violation. Virtual addresses within > the magic range bypass translation with no way to turn it off. The > firmware is being (has been?) patched to block those accesses at the > physical memory protection level so any attempt to use those virtual > addresses will fault, but if Linux wants to support this cursed > hardware and its gross spec violation then it needs to forbid any > allocation of the VA range. For a local build of an embedded system it's probably enough to set CONFIG_DEFAULT_MMAP_MIN_ADDR and CONFIG_LSM_MMAP_MIN_ADDR in order to force userspace outside of the broken address range. If that configuration can no longer run most regular userspace binaries, there is probably not much need to detect the hardware that needs it and do this automatically in the kernel, beyond perhaps some platform specific code that refuses to boot unless the config options are set this way on the affected chip revisions. Arnd