[tip:x86/asm] x86/asm: Add MONITORX/MWAITX instruction support

From: tip-bot for Huang Rui
Date: Sat Aug 22 2015 - 09:59:41 EST

Commit-ID: f96756746c7909de37db3d03ac5fd5cfb2757f38
Gitweb: http://git.kernel.org/tip/f96756746c7909de37db3d03ac5fd5cfb2757f38
Author: Huang Rui <ray.huang@xxxxxxx>
AuthorDate: Mon, 10 Aug 2015 12:19:53 +0200
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Sat, 22 Aug 2015 14:52:16 +0200

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 <ray.huang@xxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Cc: Aaron Lu <aaron.lu@xxxxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Andreas Herrmann <herrmann.der.user@xxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Dirk Brandewie <dirk.j.brandewie@xxxxxxxxx>
Cc: Fengguang Wu <fengguang.wu@xxxxxxxxx>
Cc: FrÃdÃric Weisbecker <fweisbec@xxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: John Stultz <john.stultz@xxxxxxxxxx>
Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
Cc: Len Brown <lenb@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Mike Galbraith <bitbucket@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>
Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Tony Li <tony.li@xxxxxxx>
Link: http://lkml.kernel.org/r/1439201994-28067-3-git-send-email-bp@xxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
arch/x86/include/asm/cpufeature.h | 1 +
arch/x86/include/asm/mwait.h | 45 +++++++++++++++++++++++++++++++++++++++
2 files changed, 46 insertions(+)

diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index 3d6606f..a39e570 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -176,6 +176,7 @@
#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
diff --git a/arch/x86/include/asm/mwait.h b/arch/x86/include/asm/mwait.h
index 653dfa7..c70689b 100644
--- a/arch/x86/include/asm/mwait.h
+++ b/arch/x86/include/asm/mwait.h
@@ -14,6 +14,9 @@
#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)
@@ -23,6 +26,14 @@ static inline void __monitor(const void *eax, unsigned long ecx,
:: "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;" */
@@ -30,6 +41,40 @@ static inline void __mwait(unsigned long eax, unsigned long ecx)
:: "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)
{
trace_hardirqs_on();
--
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