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SubjectRe: [PATCH 08/14] arm64: ssbd: Disable mitigation on CPU resume if required by user
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Hi,

On 05/22/2018 04:06 PM, Marc Zyngier wrote:
> On a system where firmware can dynamically change the state of the
> mitigation, the CPU will always come up with the mitigation enabled,
> including when coming back from suspend.
>
> If the user has requested "no mitigation" via a command line option,
> let's enforce it by calling into the firmware again to disable it.
>
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

Reviewed-by: Julien Grall <julien.grall@arm.com>

Cheers,

> ---
> arch/arm64/include/asm/cpufeature.h | 6 ++++++
> arch/arm64/kernel/cpu_errata.c | 8 ++++----
> arch/arm64/kernel/suspend.c | 8 ++++++++
> 3 files changed, 18 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
> index 1bacdf57f0af..d9dcb683259e 100644
> --- a/arch/arm64/include/asm/cpufeature.h
> +++ b/arch/arm64/include/asm/cpufeature.h
> @@ -553,6 +553,12 @@ static inline int arm64_get_ssbd_state(void)
> #endif
> }
>
> +#ifdef CONFIG_ARM64_SSBD
> +void arm64_set_ssbd_mitigation(bool state);
> +#else
> +static inline void arm64_set_ssbd_mitigation(bool state) {}
> +#endif
> +
> #endif /* __ASSEMBLY__ */
>
> #endif
> diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
> index 8f686f39b9c1..b4c12e9140f0 100644
> --- a/arch/arm64/kernel/cpu_errata.c
> +++ b/arch/arm64/kernel/cpu_errata.c
> @@ -297,7 +297,7 @@ void __init arm64_enable_wa2_handling(struct alt_instr *alt,
> *updptr = cpu_to_le32(aarch64_insn_gen_nop());
> }
>
> -static void do_ssbd(bool state)
> +void arm64_set_ssbd_mitigation(bool state)
> {
> switch (psci_ops.conduit) {
> case PSCI_CONDUIT_HVC:
> @@ -371,20 +371,20 @@ static bool has_ssbd_mitigation(const struct arm64_cpu_capabilities *entry,
> switch (ssbd_state) {
> case ARM64_SSBD_FORCE_DISABLE:
> pr_info_once("%s disabled from command-line\n", entry->desc);
> - do_ssbd(false);
> + arm64_set_ssbd_mitigation(false);
> required = false;
> break;
>
> case ARM64_SSBD_EL1_ENTRY:
> if (required) {
> __this_cpu_write(arm64_ssbd_callback_required, 1);
> - do_ssbd(true);
> + arm64_set_ssbd_mitigation(true);
> }
> break;
>
> case ARM64_SSBD_FORCE_ENABLE:
> pr_info_once("%s forced from command-line\n", entry->desc);
> - do_ssbd(true);
> + arm64_set_ssbd_mitigation(true);
> required = true;
> break;
>
> diff --git a/arch/arm64/kernel/suspend.c b/arch/arm64/kernel/suspend.c
> index a307b9e13392..70c283368b64 100644
> --- a/arch/arm64/kernel/suspend.c
> +++ b/arch/arm64/kernel/suspend.c
> @@ -62,6 +62,14 @@ void notrace __cpu_suspend_exit(void)
> */
> if (hw_breakpoint_restore)
> hw_breakpoint_restore(cpu);
> +
> + /*
> + * On resume, firmware implementing dynamic mitigation will
> + * have turned the mitigation on. If the user has forcefully
> + * disabled it, make sure their wishes are obeyed.
> + */
> + if (arm64_get_ssbd_state() == ARM64_SSBD_FORCE_DISABLE)
> + arm64_set_ssbd_mitigation(false);
> }
>
> /*
>

--
Julien Grall

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