[PATCH v3 2/2] cpu: fix hard lockup triggered by printk calls within scheduling context

[shechenglong <shechenglong@xfusion.com>]

relocate the printk() calls from spectre_v4_mitigations_off() and
spectre_v2_mitigations_off() into setup_system_capabilities() function,
preventing hard lockups caused by printk calls in scheduler context.

Link: https://patchwork.kernel.org/project/linux-arm-kernel/patch/20250918064907.1832-1-shechenglong@xfusion.com/
Suggested-by: Mark Rutland <mark.rutland@arm.com>
Suggested-by: Catalin Marinas <catalin.marinas@arm.com>
Suggested-by: Will Deacon <will@kernel.org>
Signed-off-by: shechenglong <shechenglong@xfusion.com>
---
 arch/arm64/include/asm/spectre.h |  1 +
 arch/arm64/kernel/cpufeature.c   |  6 ++++++
 arch/arm64/kernel/proton-pack.c  | 33 +++++++++++++++++---------------
 3 files changed, 25 insertions(+), 15 deletions(-)

diff --git a/arch/arm64/include/asm/spectre.h b/arch/arm64/include/asm/spectre.h
index 8fef12626090..900454aaa292 100644
--- a/arch/arm64/include/asm/spectre.h
+++ b/arch/arm64/include/asm/spectre.h
@@ -117,6 +117,7 @@ void spectre_bhb_patch_wa3(struct alt_instr *alt,
 			   __le32 *origptr, __le32 *updptr, int nr_inst);
 void spectre_bhb_patch_clearbhb(struct alt_instr *alt,
 				__le32 *origptr, __le32 *updptr, int nr_inst);
+void spectre_print_disabled_mitigations(void);
 
 #endif	/* __ASSEMBLY__ */
 #endif	/* __ASM_SPECTRE_H */
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 5ed401ff79e3..e25b0f84a22d 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -95,6 +95,7 @@
 #include <asm/vectors.h>
 #include <asm/virt.h>
 
+#include <asm/spectre.h>
 /* Kernel representation of AT_HWCAP and AT_HWCAP2 */
 static DECLARE_BITMAP(elf_hwcap, MAX_CPU_FEATURES) __read_mostly;
 
@@ -3875,6 +3876,11 @@ static void __init setup_system_capabilities(void)
 	 */
 	if (system_uses_ttbr0_pan())
 		pr_info("emulated: Privileged Access Never (PAN) using TTBR0_EL1 switching\n");
+
+	/*
+	 * Report Spectre mitigations status.
+	 */
+	spectre_print_disabled_mitigations();
 }
 
 void __init setup_system_features(void)
diff --git a/arch/arm64/kernel/proton-pack.c b/arch/arm64/kernel/proton-pack.c
index d833b7c1bba8..c7d70d04c164 100644
--- a/arch/arm64/kernel/proton-pack.c
+++ b/arch/arm64/kernel/proton-pack.c
@@ -91,12 +91,7 @@ early_param("nospectre_v2", parse_spectre_v2_param);
 
 static bool spectre_v2_mitigations_off(void)
 {
-	bool ret = __nospectre_v2 || cpu_mitigations_off();
-
-	if (ret)
-		pr_info_once("spectre-v2 mitigation disabled by command line option\n");
-
-	return ret;
+	return __nospectre_v2 || cpu_mitigations_off();
 }
 
 static const char *get_bhb_affected_string(enum mitigation_state bhb_state)
@@ -421,13 +416,8 @@ early_param("ssbd", parse_spectre_v4_param);
  */
 static bool spectre_v4_mitigations_off(void)
 {
-	bool ret = cpu_mitigations_off() ||
-		   __spectre_v4_policy == SPECTRE_V4_POLICY_MITIGATION_DISABLED;
-
-	if (ret)
-		pr_info_once("spectre-v4 mitigation disabled by command-line option\n");
-
-	return ret;
+	return cpu_mitigations_off() ||
+	       __spectre_v4_policy == SPECTRE_V4_POLICY_MITIGATION_DISABLED;
 }
 
 /* Do we need to toggle the mitigation state on entry to/exit from the kernel? */
@@ -1042,8 +1032,6 @@ 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 (cpu_mitigations_off() || __nospectre_bhb) {
-		pr_info_once("spectre-bhb mitigation disabled by command line option\n");
 	} else if (supports_ecbhb(SCOPE_LOCAL_CPU)) {
 		state = SPECTRE_MITIGATED;
 		set_bit(BHB_HW, &system_bhb_mitigations);
@@ -1197,3 +1185,18 @@ void unpriv_ebpf_notify(int new_state)
 		pr_err("WARNING: %s", EBPF_WARN);
 }
 #endif
+
+void spectre_print_disabled_mitigations(void)
+{
+	/* Keep a single copy of the common message suffix to avoid duplication. */
+	const char *spectre_disabled_suffix = "mitigation disabled by command-line option\n";
+
+	if (spectre_v2_mitigations_off())
+		pr_info("spectre-v2 %s", spectre_disabled_suffix);
+
+	if (spectre_v4_mitigations_off())
+		pr_info("spectre-v4 %s", spectre_disabled_suffix);
+
+	if (__nospectre_bhb || cpu_mitigations_off())
+		pr_info("spectre-bhb %s", spectre_disabled_suffix);
+}
-- 
2.33.0