arm64: Run ARCH_WORKAROUND_1 enabling code on all CPUs

Commit 73f38166 ("arm64: Advertise mitigation of Spectre-v2, or lack
thereof") changed the way we deal with ARCH_WORKAROUND_1, by moving most
of the enabling code to the .matches() callback.

This has the unfortunate effect that the workaround gets only enabled on
the first affected CPU, and no other.

In order to address this, forcefully call the .matches() callback from a
.cpu_enable() callback, which brings us back to the original behaviour.

Fixes: 73f38166 ("arm64: Advertise mitigation of Spectre-v2, or lack thereof")
Cc: <stable@vger.kernel.org>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>

arch/arm64/kernel/cpu_errata.c

@@ -599,6 +599,12 @@ check_branch_predictor(const struct arm64_cpu_capabilities *entry, int scope)
 	return (need_wa > 0);
 }
 
+static void
+cpu_enable_branch_predictor_hardening(const struct arm64_cpu_capabilities *cap)
+{
+	cap->matches(cap, SCOPE_LOCAL_CPU);
+}
+
 static const __maybe_unused struct midr_range tx2_family_cpus[] = {
 	MIDR_ALL_VERSIONS(MIDR_BRCM_VULCAN),
 	MIDR_ALL_VERSIONS(MIDR_CAVIUM_THUNDERX2),
@@ -890,9 +896,11 @@ const struct arm64_cpu_capabilities arm64_errata[] = {
 	},
 #endif
 	{
+		.desc = "Branch predictor hardening",
 		.capability = ARM64_HARDEN_BRANCH_PREDICTOR,
 		.type = ARM64_CPUCAP_LOCAL_CPU_ERRATUM,
 		.matches = check_branch_predictor,
+		.cpu_enable = cpu_enable_branch_predictor_hardening,
 	},
 #ifdef CONFIG_RANDOMIZE_BASE
 	{