ARM: virt: Add boot-time diagnostics

In order to easily detect pathological cases, print some diagnostics
when the kernel boots.

This also provides helpers to detect that HYP mode is actually available,
which can be used by other subsystems to enable HYP specific features.

Signed-off-by: Dave Martin <[e-mail]>
Signed-off-by: Marc Zyngier <[e-mail]>

arch/arm/include/asm/virt.h

···
 #define __boot_cpu_mode	(SVC_MODE)
 #endif
 
+#ifndef ZIMAGE
+void hyp_mode_check(void);
+
+/* Reports the availability of HYP mode */
+static inline bool is_hyp_mode_available(void)
+{
+	return ((__boot_cpu_mode & MODE_MASK) == HYP_MODE &&
+		!(__boot_cpu_mode & BOOT_CPU_MODE_MISMATCH));
+}
+
+/* Check if the bootloader has booted CPUs in different modes */
+static inline bool is_hyp_mode_mismatched(void)
+{
+	return !!(__boot_cpu_mode & BOOT_CPU_MODE_MISMATCH);
+}
+#endif
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* ! VIRT_H */

arch/arm/kernel/setup.c

···
 #include <asm/traps.h>
 #include <asm/unwind.h>
 #include <asm/memblock.h>
+#include <asm/virt.h>
 
 #if defined(CONFIG_DEPRECATED_PARAM_STRUCT)
 #include "compat.h"
···
 	return cmp < 0 ? -1 : cmp > 0 ? 1 : 0;
 }
 
+void __init hyp_mode_check(void)
+{
+#ifdef CONFIG_ARM_VIRT_EXT
+	if (is_hyp_mode_available()) {
+		pr_info("CPU: All CPU(s) started in HYP mode.\n");
+		pr_info("CPU: Virtualization extensions available.\n");
+	} else if (is_hyp_mode_mismatched()) {
+		pr_warn("CPU: WARNING: CPU(s) started in wrong/inconsistent modes (primary CPU mode 0x%x)\n",
+			__boot_cpu_mode & MODE_MASK);
+		pr_warn("CPU: This may indicate a broken bootloader or firmware.\n");
+	} else
+		pr_info("CPU: All CPU(s) started in SVC mode.\n");
+#endif
+}
+
 void __init setup_arch(char **cmdline_p)
 {
 	struct machine_desc *mdesc;
···
 	if (is_smp())
 		smp_init_cpus();
 #endif
+
+	if (!is_smp())
+		hyp_mode_check();
+
 	reserve_crashkernel();
 
 	tcm_init();

arch/arm/kernel/smp.c

···
 #include <asm/ptrace.h>
 #include <asm/localtimer.h>
 #include <asm/smp_plat.h>
+#include <asm/virt.h>
 
 /*
  * as from 2.5, kernels no longer have an init_tasks structure
···
 	       num_online_cpus(),
 	       bogosum / (500000/HZ),
 	       (bogosum / (5000/HZ)) % 100);
+
+	hyp_mode_check();
 }
 
 void __init smp_prepare_boot_cpu(void)