[PATCH 06/12] arm64: psci: account for Trusted OS instances

[ashwin.chaugule@linaro.org (Ashwin Chaugule)]

On 8 May 2015 at 07:36, Mark Rutland <mark.rutland@arm.com> wrote:
> Software resident in the secure world (a "Trusted OS") may cause CPU_OFF
> calls for the CPU it is resident on to be denied. Such a denial would be
> fatal for the kernel, and so we must detect when this can happen before
> the point of no return.
>
> This patch implements Trusted OS detection for PSCI 0.2+ systems, using
> MIGRATE_INFO_TYPE and MIGRATE_INFO_UP_CPU. When a trusted OS is detected
> as resident on a particular CPU, attempts to hot unplug that CPU will be
> denied early, before they can prove fatal.
>
> Trusted OS migration is not implemented by this patch. Implementation of
> migratable UP trusted OSs seems unlikely, and the right policy for
> migration is unclear (and will likely differ across implementations). As
> such, it is likely that migration will require cooperation with Trusted
> OS drivers.
>
> PSCI implementations prior to 0.1 do not provide the facility to detect
> the presence of a Trusted OS, nor the CPU any such OS is resident on, so
> without additional information it is not possible to handle Trusted OSs
> with PSCI 0.1.
>
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> ---
>  arch/arm64/kernel/psci.c | 61 ++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 61 insertions(+)
>
> diff --git a/arch/arm64/kernel/psci.c b/arch/arm64/kernel/psci.c
> index 7324db9..25e2610 100644
> --- a/arch/arm64/kernel/psci.c
> +++ b/arch/arm64/kernel/psci.c
> @@ -43,6 +43,19 @@ struct psci_power_state {
>         u8      affinity_level;
>  };
>
> +/*
> + * The CPU any Trusted OS is resident on. The trusted OS may reject CPU_OFF
> + * calls to its resident CPU, so we must avoid issuing those. We never migrate
> + * a Trusted OS even if it claims to be capable of migration -- doing so will
> + * require cooperation with a Trusted OS driver.
> + */
> +static int resident_cpu = -1;
> +
> +static bool psci_tos_resident_on(int cpu)
> +{
> +       return cpu == resident_cpu;
> +}
> +
>  struct psci_operations {
>         int (*cpu_suspend)(struct psci_power_state state,
>                            unsigned long entry_point);
> @@ -52,6 +65,7 @@ struct psci_operations {
>         int (*affinity_info)(unsigned long target_affinity,
>                         unsigned long lowest_affinity_level);
>         int (*migrate_info_type)(void);
> +       unsigned long (*migrate_info_up_cpu)(void);
>  };
>
>  static struct psci_operations psci_ops;
> @@ -172,6 +186,11 @@ static int psci_migrate_info_type(void)
>         return invoke_psci_fn(PSCI_0_2_FN_MIGRATE_INFO_TYPE, 0, 0, 0);
>  }
>
> +static unsigned long psci_migrate_info_up_cpu(void)
> +{
> +       return invoke_psci_fn(PSCI_0_2_FN64_MIGRATE_INFO_UP_CPU, 0, 0, 0);
> +}
> +
>  static int __maybe_unused cpu_psci_cpu_init_idle(struct device_node *cpu_node,
>                                                  unsigned int cpu)
>  {
> @@ -261,6 +280,40 @@ static void psci_sys_poweroff(void)
>         invoke_psci_fn(PSCI_0_2_FN_SYSTEM_OFF, 0, 0, 0);
>  }
>
> +/*
> + * Detect the presence of a resident Trusted OS which may cause CPU_OFF to
> + * return DENIED (which would be fatal).
> + */
> +static void __init psci_init_migrate(void)
> +{
> +       unsigned long cpuid;
> +       int type, cpu = -1;
> +
> +       type = psci_ops.migrate_info_type();
> +
> +       if (type == PSCI_0_2_TOS_MP) {
> +               pr_info("Trusted OS migration not required\n");
> +               return;
> +       }
> +
> +       if (type == PSCI_RET_NOT_SUPPORTED) {
> +               pr_info("MIGRATE_INFO_TYPE not supported.\n");
> +               return;
> +       }
> +
> +       if (type != PSCI_0_2_TOS_UP_MIGRATE &&
> +           type != PSCI_0_2_TOS_UP_NO_MIGRATE) {
> +               pr_err("MIGRATE_INFO_TYPE returned unknown type (%d)\n", type);
> +               return;
> +       }
> +
> +       cpuid = psci_ops.migrate_info_up_cpu();

[..]

> +       cpu = get_logical_index(cpuid);
> +       resident_cpu = cpu >= 0 ? cpu : -1;
> +
> +       pr_info("Trusted OS resident on physical CPU 0x%lx\n", cpuid);
> +}
> +
>  static void __init psci_0_2_set_functions(void)
>  {
>         pr_info("Using standard PSCI v0.2 function IDs\n");
> @@ -279,6 +332,7 @@ static void __init psci_0_2_set_functions(void)
>         psci_ops.affinity_info = psci_affinity_info;
>
>         psci_ops.migrate_info_type = psci_migrate_info_type;
> +       psci_ops.migrate_info_up_cpu = psci_migrate_info_up_cpu;
>
>         arm_pm_restart = psci_sys_reset;
>
> @@ -303,6 +357,8 @@ static int __init psci_probe(void)
>
>         psci_0_2_set_functions();
>
> +       psci_init_migrate();
> +
>         return 0;
>  }
>
> @@ -449,6 +505,11 @@ static int cpu_psci_cpu_disable(unsigned int cpu)
>         /* Fail early if we don't have CPU_OFF support */
>         if (!psci_ops.cpu_off)
>                 return -EOPNOTSUPP;
> +
> +       /* Trusted OS will deny CPU_OFF */
> +       if (psci_tos_resident_on(cpu))

IIUC, you're denying CPU_OFF even if MIGRATE_INFO_TYPE = 2. Is that correct?