Merge tag 'x86_cpu_for_v6.0_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 cpu updates from Borislav Petkov:

 - Remove the vendor check when selecting MWAIT as the default idle
   state

 - Respect idle=nomwait when supplied on the kernel cmdline

 - Two small cleanups

* tag 'x86_cpu_for_v6.0_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/cpu: Use MSR_IA32_MISC_ENABLE constants
  x86: Fix comment for X86_FEATURE_ZEN
  x86: Remove vendor checks from prefer_mwait_c1_over_halt
  x86: Handle idle=nomwait cmdline properly for x86_idle

1 files changed, 31 insertions, 13 deletions

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index d456ce21c255..58a6ea472db9 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -810,24 +810,43 @@ static void amd_e400_idle(void)
 }
 
 /*
- * Intel Core2 and older machines prefer MWAIT over HALT for C1.
- * We can't rely on cpuidle installing MWAIT, because it will not load
- * on systems that support only C1 -- so the boot default must be MWAIT.
+ * Prefer MWAIT over HALT if MWAIT is supported, MWAIT_CPUID leaf
+ * exists and whenever MONITOR/MWAIT extensions are present there is at
+ * least one C1 substate.
  *
- * Some AMD machines are the opposite, they depend on using HALT.
- *
- * So for default C1, which is used during boot until cpuidle loads,
- * use MWAIT-C1 on Intel HW that has it, else use HALT.
+ * Do not prefer MWAIT if MONITOR instruction has a bug or idle=nomwait
+ * is passed to kernel commandline parameter.
  */
 static int prefer_mwait_c1_over_halt(const struct cpuinfo_x86 *c)
 {
-	if (c->x86_vendor != X86_VENDOR_INTEL)
+	u32 eax, ebx, ecx, edx;
+
+	/* User has disallowed the use of MWAIT. Fallback to HALT */
+	if (boot_option_idle_override == IDLE_NOMWAIT)
 		return 0;
 
-	if (!cpu_has(c, X86_FEATURE_MWAIT) || boot_cpu_has_bug(X86_BUG_MONITOR))
+	/* MWAIT is not supported on this platform. Fallback to HALT */
+	if (!cpu_has(c, X86_FEATURE_MWAIT))
 		return 0;
 
-	return 1;
+	/* Monitor has a bug. Fallback to HALT */
+	if (boot_cpu_has_bug(X86_BUG_MONITOR))
+		return 0;
+
+	cpuid(CPUID_MWAIT_LEAF, &eax, &ebx, &ecx, &edx);
+
+	/*
+	 * If MWAIT extensions are not available, it is safe to use MWAIT
+	 * with EAX=0, ECX=0.
+	 */
+	if (!(ecx & CPUID5_ECX_EXTENSIONS_SUPPORTED))
+		return 1;
+
+	/*
+	 * If MWAIT extensions are available, there should be at least one
+	 * MWAIT C1 substate present.
+	 */
+	return (edx & MWAIT_C1_SUBSTATE_MASK);
 }
 
 /*
@@ -932,9 +951,8 @@ static int __init idle_setup(char *str)
 	} else if (!strcmp(str, "nomwait")) {
 		/*
 		 * If the boot option of "idle=nomwait" is added,
-		 * it means that mwait will be disabled for CPU C2/C3
-		 * states. In such case it won't touch the variable
-		 * of boot_option_idle_override.
+		 * it means that mwait will be disabled for CPU C1/C2/C3
+		 * states.
 		 */
 		boot_option_idle_override = IDLE_NOMWAIT;
 	} else