x86: prevent unconditional writes to DebugCtl MSR
Otherwise, enabling (or better, subsequent disabling) of single
stepping would cause a kernel oops on CPUs not having this MSR.
The patch could have been added a conditional to the MSR write in
user_disable_single_step(), but centralizing the updates seems safer
and (looking forward) better manageable.
Signed-off-by: Jan Beulich <jbeulich@novell.com>
Cc: Markus Metzger <markus.t.metzger@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/asm-x86/processor.h b/include/asm-x86/processor.h
index cc02683..40227c9 100644
--- a/include/asm-x86/processor.h
+++ b/include/asm-x86/processor.h
@@ -741,6 +741,15 @@
extern void cpu_init(void);
extern void init_gdt(int cpu);
+static inline void update_debugctlmsr(unsigned long debugctlmsr)
+{
+#ifndef CONFIG_X86_DEBUGCTLMSR
+ if (boot_cpu_data.x86 < 6)
+ return;
+#endif
+ wrmsrl(MSR_IA32_DEBUGCTLMSR, debugctlmsr);
+}
+
/*
* from system description table in BIOS. Mostly for MCA use, but
* others may find it useful: