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

[Yeoreum Yun <yeoreum.yun@arm.com>]

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@arm.com>
> > Reviewed-by: Catalin Marinas <catalin.marinas@arm.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