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

Documentation/admin-guide/pm/cpuidle.rst

@@ -612,8 +612,8 @@ the ``menu`` governor to be used on the systems that use the ``ladder`` governor
 by default this way, for example.
 
 The other kernel command line parameters controlling CPU idle time management
-described below are only relevant for the *x86* architecture and some of
-them affect Intel processors only.
+described below are only relevant for the *x86* architecture and references
+to ``intel_idle`` affect Intel processors only.
 
 The *x86* architecture support code recognizes three kernel command line
 options related to CPU idle time management: ``idle=poll``, ``idle=halt``,
@@ -635,10 +635,13 @@ idle, so it very well may hurt single-thread computations performance as well as
 energy-efficiency.  Thus using it for performance reasons may not be a good idea
 at all.]
 
-The ``idle=nomwait`` option disables the ``intel_idle`` driver and causes
-``acpi_idle`` to be used (as long as all of the information needed by it is
-there in the system's ACPI tables), but it is not allowed to use the
-``MWAIT`` instruction of the CPUs to ask the hardware to enter idle states.
+The ``idle=nomwait`` option prevents the use of ``MWAIT`` instruction of
+the CPU to enter idle states. When this option is used, the ``acpi_idle``
+driver will use the ``HLT`` instruction instead of ``MWAIT``. On systems
+running Intel processors, this option disables the ``intel_idle`` driver
+and forces the use of the ``acpi_idle`` driver instead. Note that in either
+case, ``acpi_idle`` driver will function only if all the information needed
+by it is in the system's ACPI tables.
 
 In addition to the architecture-level kernel command line options affecting CPU
 idle time management, there are parameters affecting individual ``CPUIdle``

arch/x86/include/asm/cpufeatures.h

@@ -219,7 +219,7 @@
 #define X86_FEATURE_IBRS		( 7*32+25) /* Indirect Branch Restricted Speculation */
 #define X86_FEATURE_IBPB		( 7*32+26) /* Indirect Branch Prediction Barrier */
 #define X86_FEATURE_STIBP		( 7*32+27) /* Single Thread Indirect Branch Predictors */
-#define X86_FEATURE_ZEN			( 7*32+28) /* "" CPU is AMD family 0x17 or above (Zen) */
+#define X86_FEATURE_ZEN			(7*32+28) /* "" CPU based on Zen microarchitecture */
 #define X86_FEATURE_L1TF_PTEINV		( 7*32+29) /* "" L1TF workaround PTE inversion */
 #define X86_FEATURE_IBRS_ENHANCED	( 7*32+30) /* Enhanced IBRS */
 #define X86_FEATURE_MSR_IA32_FEAT_CTL	( 7*32+31) /* "" MSR IA32_FEAT_CTL configured */

arch/x86/include/asm/mwait.h

@@ -13,6 +13,7 @@
 #define MWAIT_SUBSTATE_SIZE		4
 #define MWAIT_HINT2CSTATE(hint)		(((hint) >> MWAIT_SUBSTATE_SIZE) & MWAIT_CSTATE_MASK)
 #define MWAIT_HINT2SUBSTATE(hint)	((hint) & MWAIT_CSTATE_MASK)
+#define MWAIT_C1_SUBSTATE_MASK  0xf0
 
 #define CPUID_MWAIT_LEAF		5
 #define CPUID5_ECX_EXTENSIONS_SUPPORTED 0x1

arch/x86/kernel/cpu/intel.c

@@ -682,9 +682,9 @@ static void init_intel(struct cpuinfo_x86 *c)
 		unsigned int l1, l2;
 
 		rdmsr(MSR_IA32_MISC_ENABLE, l1, l2);
-		if (!(l1 & (1<<11)))
+		if (!(l1 & MSR_IA32_MISC_ENABLE_BTS_UNAVAIL))
 			set_cpu_cap(c, X86_FEATURE_BTS);
-		if (!(l1 & (1<<12)))
+		if (!(l1 & MSR_IA32_MISC_ENABLE_PEBS_UNAVAIL))
 			set_cpu_cap(c, X86_FEATURE_PEBS);
 	}
 

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