[PATCH] arm64: proton-pack: Fix hard lockup when !MITIGATE_SPECTRE_BRANCH_HISTORY

[Vladimir Zapolskiy]

On 11/17/25 07:12, Jonathan Marek wrote:
> The "drop print" commit removed the whole branch and not just the print.
> For some ARM64 cpus, this leads to hard lockup when
> CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY is not enabled.
> 
> Fixes: 62e72463ca71 ("arm64: proton-pack: Drop print when !CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY")
> ---
>   arch/arm64/kernel/proton-pack.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/arch/arm64/kernel/proton-pack.c b/arch/arm64/kernel/proton-pack.c
> index c7d70d04c164c..80a580e019c50 100644
> --- a/arch/arm64/kernel/proton-pack.c
> +++ b/arch/arm64/kernel/proton-pack.c
> @@ -1032,6 +1032,8 @@ void spectre_bhb_enable_mitigation(const struct arm64_cpu_capabilities *entry)
>   
>   	if (arm64_get_spectre_v2_state() == SPECTRE_VULNERABLE) {
>   		/* No point mitigating Spectre-BHB alone. */
> +	} else if (!IS_ENABLED(CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY)) {
> +		/* Do nothing */
>   	} else if (supports_ecbhb(SCOPE_LOCAL_CPU)) {
>   		state = SPECTRE_MITIGATED;
>   		set_bit(BHB_HW, &system_bhb_mitigations);


If CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY is unset, the fix is needed
to boot Linux on Lantronix SM8450-HDK and SM8550-HDK boards, which are
otherwise broken since v6.18-rc6.

Reviewed-by: Vladimir Zapolskiy <vladimir.zapolskiy at linaro.org>
Tested-by: Vladimir Zapolskiy <vladimir.zapolskiy at linaro.org>

-- 
Best wishes,
Vladimir