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Fri, 26 Jan 2024 15:14:35 -0500 (EST) X-Mailer: MessagingEngine.com Webmail Interface User-Agent: Cyrus-JMAP/3.11.0-alpha0-119-ga8b98d1bd8-fm-20240108.001-ga8b98d1b Precedence: bulk X-Mailing-List: linux-cxl@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-Id: In-Reply-To: References: Date: Fri, 26 Jan 2024 21:14:15 +0100 From: "Arnd Bergmann" To: "Mathieu Desnoyers" , "Dan Williams" , "Vishal Verma" , "Dave Jiang" , "Matthew Wilcox" , "Andrew Morton" , "Linus Torvalds" , linux-mm , Linux-Arch , nvdimm@lists.linux.dev, linux-cxl@vger.kernel.org, linux-kernel , "Russell King" Subject: Re: [REGRESSION] v5.13: FS_DAX unavailable on 32-bit ARM Content-Type: text/plain On Fri, Jan 26, 2024, at 20:33, Mathieu Desnoyers wrote: > > A) I have prepared a patch series introducing cache_is_aliasing() with > new Kconfig > options: > > * ARCH_HAS_CACHE_ALIASING > * ARCH_HAS_CACHE_ALIASING_DYNAMIC > > and implemented it for all architectures. The "DYNAMIC" implementation > implements cache_is_aliasing() as a runtime check, which is what is needed > on architectures like 32-bit ARM. > > With this we can basically narrow down the list of architectures which are > unsupported by DAX to those which are really affected, without actually solving > the issue for architectures with virtually aliased dcaches. The dynamic option should only be required when building for ARMv6, which is really rare. On an ARMv7-only configuration, we know that the dcache is non-aliasing, so the compile-time check should be sufficient. Even on ARMv6, this could be done as a compile-time choice by platform, since we mostly know what the chips can do: bcm2835, imx3, wm8750 and s3c64xx are non-aliasing because they are limited to 16KB L1 caches, while omap2 and as2500 are aliasing with 32KB caches. With realview/integrator it depends on the exact CPU that was installed. Arnd