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SubjectRe: [PATCH 04/14] arm64: Add ARCH_WORKAROUND_2 probing
On Tue, May 22, 2018 at 04:06:38PM +0100, Marc Zyngier wrote:
> As for Spectre variant-2, we rely on SMCCC 1.1 to provide the
> discovery mechanism for detecting the SSBD mitigation.
>
> A new capability is also allocated for that purpose, and a
> config option.
>
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

Reviewed-by: Mark Rutland <mark.rutland@arm.com>

[...]

> +static void do_ssbd(bool state)
> +{
> + switch (psci_ops.conduit) {
> + case PSCI_CONDUIT_HVC:
> + arm_smccc_1_1_hvc(ARM_SMCCC_ARCH_WORKAROUND_2, state, NULL);
> + break;
> +
> + case PSCI_CONDUIT_SMC:
> + arm_smccc_1_1_smc(ARM_SMCCC_ARCH_WORKAROUND_2, state, NULL);
> + break;
> +
> + default:
> + WARN_ON_ONCE(1);
> + break;
> + }
> +}
> +
> +static bool has_ssbd_mitigation(const struct arm64_cpu_capabilities *entry,
> + int scope)
> +{
> + struct arm_smccc_res res;
> + bool supported = true;
> +
> + WARN_ON(scope != SCOPE_LOCAL_CPU || preemptible());
> +
> + if (psci_ops.smccc_version == SMCCC_VERSION_1_0)
> + return false;
> +
> + /*
> + * The probe function return value is either negative
> + * (unsupported or mitigated), positive (unaffected), or zero
> + * (requires mitigation). We only need to do anything in the
> + * last case.
> + */
> + switch (psci_ops.conduit) {
> + case PSCI_CONDUIT_HVC:
> + arm_smccc_1_1_hvc(ARM_SMCCC_ARCH_FEATURES_FUNC_ID,
> + ARM_SMCCC_ARCH_WORKAROUND_2, &res);
> + if ((int)res.a0 != 0)
> + supported = false;
> + break;
> +
> + case PSCI_CONDUIT_SMC:
> + arm_smccc_1_1_smc(ARM_SMCCC_ARCH_FEATURES_FUNC_ID,
> + ARM_SMCCC_ARCH_WORKAROUND_2, &res);
> + if ((int)res.a0 != 0)
> + supported = false;
> + break;

Once this is merged, I'll rebase my SMCCCC conduit cleanup atop.

Mark.

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