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Message-ID: <Y1gqTM19oLeN59Kl@shell.armlinux.org.uk>
Date: Tue, 25 Oct 2022 19:26:20 +0100
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Yury Norov <yury.norov@...il.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
Catalin Marinas <catalin.marinas@....com>,
Mark Rutland <mark.rutland@....com>,
Will Deacon <will@...nel.org>,
linux-arm-kernel@...ts.infradead.org,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Alexey Klimov <klimov.linux@...il.com>,
Andy Shevchenko <andy.shevchenko@...il.com>,
Andy Whitcroft <apw@...onical.com>,
Dennis Zhou <dennis@...nel.org>,
Geert Uytterhoeven <geert@...ux-m68k.org>,
Guenter Roeck <linux@...ck-us.net>,
Kees Cook <keescook@...omium.org>,
Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [PATCH 1/2] bitmap: add sanity check function for find_bit()
On Tue, Oct 25, 2022 at 10:11:51AM -0700, Yury Norov wrote:
> ARMv6 may or may not support unaligned access depending on SCTLR.U
> bit. This is what Russell was concerned about in the other email.
> As far as I understand, linux enables that feature.
However, we still support ARMv5 and ARMv4, both of which _trap_ every
unaligned access, which will make a findbit call with an unaligned
pointer using word loads painfully expensive. This is the main reason
we haven't used word loads in the findbit ops.
As mentioned, I have patches that do change that (and convert the
thing to use assembly macros to make updates much easier.)
--
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!
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