Re: [PATCH] AArch64: Add asymmetric faulting mode for tag violations in mem.tagging tunable

[Szabolcs Nagy <Szabolcs.Nagy@arm.com>]

The 06/27/2022 18:00, Tejas Belagod wrote:
> Hi,
> 
> The new asymmetric mode is available when HWCAP2_MTE3 is set (support is
> available), bit2 is set in the tunable (user request per application),
> and the system is configured such that the asymmetric mode is preferred over
> sync or async (per-cpu system-wide setting).
> 
> OK for master?
> 
> Thanks,
> Tejas.

This is ok.

Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>


> diff --git a/manual/tunables.texi b/manual/tunables.texi
> index 1482412078d21cc8da22a62ff4acac3e5297eff9..1d6befaf4a40865a4eee6a6a7a34fa39258f764b 100644
> --- a/manual/tunables.texi
> +++ b/manual/tunables.texi
> @@ -602,6 +602,9 @@ Bit 1 enables precise faulting mode for tag violations on systems that
>  support deferred tag violation reporting.  This may cause programs
>  to run more slowly.
>  
> +Bit 2 enables either precise or deferred faulting mode for tag violations
> +whichever is preferred by the system.
> +
>  Other bits are currently reserved.
>  
>  @Theglibc{} startup code will automatically enable memory tagging
> diff --git a/sysdeps/unix/sysv/linux/aarch64/cpu-features.c b/sysdeps/unix/sysv/linux/aarch64/cpu-features.c
> index 41dda8d00327e56b6c85a07eb68435de1dda5dae..d14c0f4e1f2905148ac55a4569fd3e12f9a1d7fe 100644
> --- a/sysdeps/unix/sysv/linux/aarch64/cpu-features.c
> +++ b/sysdeps/unix/sysv/linux/aarch64/cpu-features.c
> @@ -108,7 +108,13 @@ init_cpu_features (struct cpu_features *cpu_features)
>    TUNABLE_SET (glibc, mem, tagging, cpu_features->mte_state);
>  # endif
>  
> -  if (cpu_features->mte_state & 2)
> +  if (cpu_features->mte_state & 4)
> +    /* Enable choosing system-preferred faulting mode.  */
> +    __prctl (PR_SET_TAGGED_ADDR_CTRL,
> +	     (PR_TAGGED_ADDR_ENABLE | PR_MTE_TCF_SYNC | PR_MTE_TCF_ASYNC
> +	      | MTE_ALLOWED_TAGS),
> +	     0, 0, 0);
> +  else if (cpu_features->mte_state & 2)
>      __prctl (PR_SET_TAGGED_ADDR_CTRL,
>  	     (PR_TAGGED_ADDR_ENABLE | PR_MTE_TCF_SYNC | MTE_ALLOWED_TAGS),
>  	     0, 0, 0);