linux-kernel - Re: [PATCH v8 04/12] arm64: support WFET in smp_cond_relaxed

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aWAjMbSqN2g7v58Z@willie-the-truck>
Date: Thu, 8 Jan 2026 21:35:45 +0000
From: Will Deacon <will@...nel.org>
To: Ankur Arora <ankur.a.arora@...cle.com>
Cc: linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-pm@...r.kernel.org,
	bpf@...r.kernel.org, arnd@...db.de, catalin.marinas@....com,
	peterz@...radead.org, akpm@...ux-foundation.org,
	mark.rutland@....com, harisokn@...zon.com, cl@...two.org,
	ast@...nel.org, rafael@...nel.org, daniel.lezcano@...aro.org,
	memxor@...il.com, zhenglifeng1@...wei.com,
	xueshuai@...ux.alibaba.com, joao.m.martins@...cle.com,
	boris.ostrovsky@...cle.com, konrad.wilk@...cle.com
Subject: Re: [PATCH v8 04/12] arm64: support WFET in
 smp_cond_relaxed_timeout()

On Sun, Dec 14, 2025 at 08:49:11PM -0800, Ankur Arora wrote:
> +#define __CMPWAIT_CASE(w, sfx, sz)						\
> +static inline void __cmpwait_case_##sz(volatile void *ptr,			\
> +				       unsigned long val,			\
> +				       s64 timeout_ns)				\
> +{										\
> +	unsigned long tmp;							\
> +										\
> +	if (!alternative_has_cap_unlikely(ARM64_HAS_WFXT) || timeout_ns <= 0) {	\
> +		asm volatile(							\
> +		"	sevl\n"							\
> +		"	wfe\n"							\
> +		"	ldxr" #sfx "\t%" #w "[tmp], %[v]\n"			\
> +		"	eor	%" #w "[tmp], %" #w "[tmp], %" #w "[val]\n"	\
> +		"	cbnz	%" #w "[tmp], 1f\n"				\
> +		"	wfe\n"							\
> +		"1:"								\
> +		: [tmp] "=&r" (tmp), [v] "+Q" (*(u##sz *)ptr)			\
> +		: [val] "r" (val));						\
> +	} else {								\
> +		u64 ecycles = arch_timer_read_counter() +			\
> +				NSECS_TO_CYCLES(timeout_ns);			\
> +		asm volatile(							\
> +		"	sevl\n"							\
> +		"	wfe\n"							\
> +		"	ldxr" #sfx "\t%" #w "[tmp], %[v]\n"			\
> +		"	eor	%" #w "[tmp], %" #w "[tmp], %" #w "[val]\n"	\
> +		"	cbnz	%" #w "[tmp], 2f\n"				\
> +		"	msr s0_3_c1_c0_0, %[ecycles]\n"				\
> +		"2:"								\
> +		: [tmp] "=&r" (tmp), [v] "+Q" (*(u##sz *)ptr)			\
> +		: [val] "r" (val), [ecycles] "r" (ecycles));			\
> +	}									\

Why not have a separate helper for the WFXT version and avoid the runtime
check on timeout_ns?

Will