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

Will Deacon
2026-01-19T15:57:23Z

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?

Will