x86/asm: Add MONITORX/MWAITX instruction support

AMD Carrizo processors (Family 15h, Models 60h-6fh) added a new
feature called MWAITX (MWAIT with extensions) as an extension to
MONITOR/MWAIT.

This new instruction controls a configurable timer which causes
the core to exit wait state on timer expiration, in addition to
"normal" MWAIT condition of reading from a monitored VA.

Compared to MONITOR/MWAIT, there are minor differences in opcode
and input parameters:

MWAITX ECX[1]: enable timer if set
MWAITX EBX[31:0]: max wait time expressed in SW P0 clocks ==
TSC. The software P0 frequency is the same as the TSC frequency.

MWAIT MWAITX
opcode 0f 01 c9 | 0f 01 fb
ECX[0] value of RFLAGS.IF seen by instruction
ECX[1] unused/#GP if set | enable timer if set
ECX[31:2] unused/#GP if set
EAX unused (reserve for hint)
EBX[31:0] unused | max wait time (SW P0 == TSC)

MONITOR MONITORX
opcode 0f 01 c8 | 0f 01 fa
EAX (logical) address to monitor
ECX #GP if not zero

Max timeout = EBX/(TSC frequency)

Signed-off-by: Huang Rui <[e-mail]>
Signed-off-by: Borislav Petkov <[e-mail]>
Cc: Aaron Lu <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Andreas Herrmann <[e-mail]>
Cc: Andy Lutomirski <[e-mail]>
Cc: Dave Hansen <[e-mail]>
Cc: Dirk Brandewie <[e-mail]>
Cc: Fengguang Wu <[e-mail]>
Cc: Frédéric Weisbecker <[e-mail]>
Cc: H. Peter Anvin <[e-mail]>
Cc: John Stultz <[e-mail]>
Cc: Josh Triplett <[e-mail]>
Cc: Len Brown <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Mike Galbraith <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Rafael J. Wysocki <[e-mail]>
Cc: Ross Zwisler <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Tony Li <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

arch/x86/include/asm/cpufeature.h

···
 #define X86_FEATURE_PERFCTR_NB  ( 6*32+24) /* NB performance counter extensions */
 #define X86_FEATURE_BPEXT	(6*32+26) /* data breakpoint extension */
 #define X86_FEATURE_PERFCTR_L2	( 6*32+28) /* L2 performance counter extensions */
+#define X86_FEATURE_MWAITX	( 6*32+29) /* MWAIT extension (MONITORX/MWAITX) */
 
 /*
  * Auxiliary flags: Linux defined - For features scattered in various

arch/x86/include/asm/mwait.h

···
 #define CPUID5_ECX_INTERRUPT_BREAK	0x2
 
 #define MWAIT_ECX_INTERRUPT_BREAK	0x1
+#define MWAITX_ECX_TIMER_ENABLE		BIT(1)
+#define MWAITX_MAX_LOOPS		((u32)-1)
+#define MWAITX_DISABLE_CSTATES		0xf
 
 static inline void __monitor(const void *eax, unsigned long ecx,
 			     unsigned long edx)
···
 		     :: "a" (eax), "c" (ecx), "d"(edx));
 }
 
+static inline void __monitorx(const void *eax, unsigned long ecx,
+			      unsigned long edx)
+{
+	/* "monitorx %eax, %ecx, %edx;" */
+	asm volatile(".byte 0x0f, 0x01, 0xfa;"
+		     :: "a" (eax), "c" (ecx), "d"(edx));
+}
+
 static inline void __mwait(unsigned long eax, unsigned long ecx)
 {
 	/* "mwait %eax, %ecx;" */
 	asm volatile(".byte 0x0f, 0x01, 0xc9;"
 		     :: "a" (eax), "c" (ecx));
+}
+
+/*
+ * MWAITX allows for a timer expiration to get the core out a wait state in
+ * addition to the default MWAIT exit condition of a store appearing at a
+ * monitored virtual address.
+ *
+ * Registers:
+ *
+ * MWAITX ECX[1]: enable timer if set
+ * MWAITX EBX[31:0]: max wait time expressed in SW P0 clocks. The software P0
+ * frequency is the same as the TSC frequency.
+ *
+ * Below is a comparison between MWAIT and MWAITX on AMD processors:
+ *
+ *                 MWAIT                           MWAITX
+ * opcode          0f 01 c9           |            0f 01 fb
+ * ECX[0]                  value of RFLAGS.IF seen by instruction
+ * ECX[1]          unused/#GP if set  |            enable timer if set
+ * ECX[31:2]                     unused/#GP if set
+ * EAX                           unused (reserve for hint)
+ * EBX[31:0]       unused             |            max wait time (P0 clocks)
+ *
+ *                 MONITOR                         MONITORX
+ * opcode          0f 01 c8           |            0f 01 fa
+ * EAX                     (logical) address to monitor
+ * ECX                     #GP if not zero
+ */
+static inline void __mwaitx(unsigned long eax, unsigned long ebx,
+			    unsigned long ecx)
+{
+	/* "mwaitx %eax, %ebx, %ecx;" */
+	asm volatile(".byte 0x0f, 0x01, 0xfb;"
+		     :: "a" (eax), "b" (ebx), "c" (ecx));
 }
 
 static inline void __sti_mwait(unsigned long eax, unsigned long ecx)