arm64: proton-pack: Fix hard lockup when !MITIGATE_SPECTRE_BRANCH_HISTORY

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")
Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Signed-off-by: Will Deacon <will@kernel.org>

diff --git a/arch/arm64/kernel/proton-pack.c b/arch/arm64/kernel/proton-pack.c
index c7d70d04c164ca5fff67c02e22af38c7c93df249..80a580e019c5017e02f14f324d444964cab883d6 100644 (file)
--- 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);