Re: [PATCH v2 6/9] target/arm: Factor out code for setting MTE TCF0 field

["Alex Bennée" <alex.bennee@linaro.org>]

Gustavo Romero <gustavo.romero@linaro.org> writes:

> Factor out the code used for setting the MTE TCF0 field from the prctl
> code into a convenient function. Other subsystems, like gdbstub, need to
> set this field as well, so keep it as a separate function to avoid
> duplication and ensure consistency in how this field is set across the
> board.
>
> Signed-off-by: Gustavo Romero <gustavo.romero@linaro.org>
> ---
>  linux-user/aarch64/target_prctl.h | 22 ++-----------
>  target/arm/mte.h                  | 53 +++++++++++++++++++++++++++++++
>  2 files changed, 55 insertions(+), 20 deletions(-)
>  create mode 100644 target/arm/mte.h
>
> diff --git a/linux-user/aarch64/target_prctl.h b/linux-user/aarch64/target_prctl.h
> index aa8e203c15..8a11404222 100644
> --- a/linux-user/aarch64/target_prctl.h
> +++ b/linux-user/aarch64/target_prctl.h
> @@ -7,6 +7,7 @@
>  #define AARCH64_TARGET_PRCTL_H
>  
>  #include "target/arm/cpu-features.h"
> +#include "target/arm/mte.h"

We are moving a helper that is TCG only but using the common code path.
I suspect the prototype better belongs in target/arm/tcg/mte_helper.h or
possibly target/arm/tcg/mte_user_helper.h if we are just using it for
user-mode.

>  
>  static abi_long do_prctl_sve_get_vl(CPUArchState *env)
>  {
> @@ -173,26 +174,7 @@ static abi_long do_prctl_set_tagged_addr_ctrl(CPUArchState *env, abi_long arg2)
>      env->tagged_addr_enable = arg2 & PR_TAGGED_ADDR_ENABLE;
>  
>      if (cpu_isar_feature(aa64_mte, cpu)) {
> -        /*
> -         * Write PR_MTE_TCF to SCTLR_EL1[TCF0].
> -         *
> -         * The kernel has a per-cpu configuration for the sysadmin,
> -         * /sys/devices/system/cpu/cpu<N>/mte_tcf_preferred,
> -         * which qemu does not implement.
> -         *
> -         * Because there is no performance difference between the modes, and
> -         * because SYNC is most useful for debugging MTE errors, choose SYNC
> -         * as the preferred mode.  With this preference, and the way the API
> -         * uses only two bits, there is no way for the program to select
> -         * ASYMM mode.
> -         */
> -        unsigned tcf = 0;
> -        if (arg2 & PR_MTE_TCF_SYNC) {
> -            tcf = 1;
> -        } else if (arg2 & PR_MTE_TCF_ASYNC) {
> -            tcf = 2;
> -        }
> -        env->cp15.sctlr_el[1] = deposit64(env->cp15.sctlr_el[1], 38, 2, tcf);
> +        set_mte_tcf0(env, arg2);
>  
>          /*
>           * Write PR_MTE_TAG to GCR_EL1[Exclude].
> diff --git a/target/arm/mte.h b/target/arm/mte.h
> new file mode 100644
> index 0000000000..89712aad70
> --- /dev/null
> +++ b/target/arm/mte.h
> @@ -0,0 +1,53 @@
> +/*
> + * ARM MemTag convenience functions.
> + *
> + * Copyright (c) 2024 Linaro, Ltd.
> + *
> + * This library is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU Lesser General Public
> + * License as published by the Free Software Foundation; either
> + * version 2.1 of the License, or (at your option) any later version.
> + *
> + * This library is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * Lesser General Public License for more details.
> + *
> + * You should have received a copy of the GNU Lesser General Public
> + * License along with this library; if not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#ifndef MTE_H
> +#define MTE_H
> +
> +#ifdef CONFIG_TCG
> +#ifdef CONFIG_USER_ONLY
> +#include "sys/prctl.h"
> +
> +static void set_mte_tcf0(CPUArchState *env, abi_long value)

Same comments as Phil regarding should it be inline, add a prefix etc...

> +{
> +    /*
> +     * Write PR_MTE_TCF to SCTLR_EL1[TCF0].
> +     *
> +     * The kernel has a per-cpu configuration for the sysadmin,
> +     * /sys/devices/system/cpu/cpu<N>/mte_tcf_preferred,
> +     * which qemu does not implement.
> +     *
> +     * Because there is no performance difference between the modes, and
> +     * because SYNC is most useful for debugging MTE errors, choose SYNC
> +     * as the preferred mode.  With this preference, and the way the API
> +     * uses only two bits, there is no way for the program to select
> +     * ASYMM mode.
> +     */
> +    unsigned tcf = 0;
> +    if (value & PR_MTE_TCF_SYNC) {
> +        tcf = 1;
> +    } else if (value & PR_MTE_TCF_ASYNC) {
> +        tcf = 2;
> +    }
> +    env->cp15.sctlr_el[1] = deposit64(env->cp15.sctlr_el[1], 38, 2, tcf);
> +}
> +#endif /* CONFIG_USER_ONLY */
> +#endif /* CONFIG_TCG */
> +
> +#endif /* MTE_H */

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro