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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 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 X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 5F45B1C0004 X-Stat-Signature: m6j78mtocwyaiiiqt11s15c43wweppcq X-HE-Tag: 1706300079-322722 X-HE-Meta: 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 b7vfwmWr WKugYleZmCHuxvu5k4/YIXVlCUKVBY/rBMnZQ6a4Q8dFarnz0bL1MWHphlpt3vLhIUC+peuHir43QBjb3VHVwPfjV+y79Hmx3DlgACk+A8qNnwg31KJb814TTo7FPE8SiaAEUMW3Z0xVTqlO30jacR+YrZD9wRDZfxYRjfsUeUm96yhBLFBFrP4nGYdI8+DhgFbmhMinqiL25d710RCSui6NETw== 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: List-Subscribe: List-Unsubscribe: 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