linux-kernel - Re: [PATCH v11 RESEND 5/9] arm64: futex: refactor futex atomic operation

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Message-ID: <aW6t7EzWLig2AN3g@e129823.arm.com>
Date: Mon, 19 Jan 2026 22:19:24 +0000
From: Yeoreum Yun <yeoreum.yun@....com>
To: Will Deacon <will@...nel.org>
Cc: catalin.marinas@....com, maz@...nel.org, broonie@...nel.org,
	oliver.upton@...ux.dev, miko.lenczewski@....com,
	kevin.brodsky@....com, ardb@...nel.org, suzuki.poulose@....com,
	lpieralisi@...nel.org, yangyicong@...ilicon.com,
	scott@...amperecomputing.com, joey.gouly@....com,
	yuzenghui@...wei.com, pbonzini@...hat.com, shuah@...nel.org,
	mark.rutland@....com, arnd@...db.de,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	kvmarm@...ts.linux.dev, kvm@...r.kernel.org,
	linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v11 RESEND 5/9] arm64: futex: refactor futex atomic
 operation

Hi Will,

> On Sun, Dec 14, 2025 at 11:22:44AM +0000, Yeoreum Yun wrote:
> > Refactor futex atomic operations using ll/sc method with
> > clearing PSTATE.PAN to prepare to apply FEAT_LSUI on them.
> >
> > Signed-off-by: Yeoreum Yun <yeoreum.yun@....com>
> > Reviewed-by: Catalin Marinas <catalin.marinas@....com>
> > ---
> >  arch/arm64/include/asm/futex.h | 128 +++++++++++++++++++++------------
> >  1 file changed, 82 insertions(+), 46 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/futex.h b/arch/arm64/include/asm/futex.h
> > index bc06691d2062..f8cb674bdb3f 100644
> > --- a/arch/arm64/include/asm/futex.h
> > +++ b/arch/arm64/include/asm/futex.h
> > @@ -7,17 +7,21 @@
> >
> >  #include <linux/futex.h>
> >  #include <linux/uaccess.h>
> > +#include <linux/stringify.h>
> >
> >  #include <asm/errno.h>
> >
> >  #define FUTEX_MAX_LOOPS	128 /* What's the largest number you can think of? */
> >
> > -#define __futex_atomic_op(insn, ret, oldval, uaddr, tmp, oparg)		\
> > -do {									\
> > +#define LLSC_FUTEX_ATOMIC_OP(op, insn)					\
> > +static __always_inline int						\
> > +__llsc_futex_atomic_##op(int oparg, u32 __user *uaddr, int *oval)	\
> > +{									\
> >  	unsigned int loops = FUTEX_MAX_LOOPS;				\
> > +	int ret, oldval, tmp;						\
> >  									\
> >  	uaccess_enable_privileged();					\
> > -	asm volatile(							\
> > +	asm volatile("// __llsc_futex_atomic_" #op "\n"			\
> >  "	prfm	pstl1strm, %2\n"					\
> >  "1:	ldxr	%w1, %2\n"						\
> >  	insn "\n"							\
> > @@ -35,45 +39,103 @@ do {									\
> >  	: "r" (oparg), "Ir" (-EAGAIN)					\
> >  	: "memory");							\
> >  	uaccess_disable_privileged();					\
> > -} while (0)
> > +									\
> > +	if (!ret)							\
> > +		*oval = oldval;						\
> > +									\
> > +	return ret;							\
> > +}
> > +
> > +LLSC_FUTEX_ATOMIC_OP(add, "add	%w3, %w1, %w5")
> > +LLSC_FUTEX_ATOMIC_OP(or,  "orr	%w3, %w1, %w5")
> > +LLSC_FUTEX_ATOMIC_OP(and, "and	%w3, %w1, %w5")
> > +LLSC_FUTEX_ATOMIC_OP(eor, "eor	%w3, %w1, %w5")
> > +LLSC_FUTEX_ATOMIC_OP(set, "mov	%w3, %w5")
>
> Since you're reworking this code, how about we take the opportunity to
> use named arguments instead of the numbers?

Okay. Let me try this.


--
Sincerely,
Yeoreum Yun