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

Yeoreum Yun
2026-01-19T22:20:34Z

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