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Date: Wed, 9 Apr 2008 16:21:06 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To: "H. Peter Anvin" <hpa@...or.com>
Cc: akpm@...ux-foundation.org, Ingo Molnar <mingo@...e.hu>,
linux-kernel@...r.kernel.org, Andi Kleen <andi@...stfloor.org>,
Rusty Russell <rusty@...tcorp.com.au>, Andi Kleen <ak@....de>,
Chuck Ebbert <cebbert@...hat.com>,
Christoph Hellwig <hch@...radead.org>,
Jeremy Fitzhardinge <jeremy@...p.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Adrian Bunk <bunk@...sta.de>,
Alexey Dobriyan <adobriyan@...il.com>, akpm@...l.org
Subject: Re: [patch 13/17] Immediate Values - x86 Optimization (updated)
* H. Peter Anvin (hpa@...or.com) wrote:
> Mathieu Desnoyers wrote:
>> Ok, so the most flexible solution that I see, that should fit for both
>> x86 and x86_64 would be :
>> 1 byte : "=q" : "a", "b", "c", or "d" register for the i386. For
>> x86-64 it is equivalent to "r" class (for 8-bit
>> instructions that do not use upper halves).
>> 2, 4, 8 bytes : "=r" : A register operand is allowed provided that it is
>> in a
>> general register.
>
> Any reason to keep carrying this completely misleading comment chunk still?
>
> -hpa
Hrm, since even the nmi-safe version supports REX-prefixed instructions,
there is no need for an =q constraint on single-byte immediate values
anymore. (thanks to your "discard" section used in the nmi-safe version)
Here is the updated patch for the "[patch 13/17] Immediate Values - x86
Optimization". Thanks!
Mathieu
Immediate Values - x86 Optimization
x86 optimization of the immediate values which uses a movl with code patching
to set/unset the value used to populate the register used as variable source.
Changelog:
- Use text_poke_early with cr0 WP save/restore to patch the bypass. We are doing
non atomic writes to a code region only touched by us (nobody can execute it
since we are protected by the imv_mutex).
- Use $0 instead of %2 with (0) operand.
- Add x86_64 support, ready for i386+x86_64 -> x86 merge.
- Use asm-x86/asm.h.
- Bugfix : 8 bytes 64 bits immediate value was declared as "4 bytes" in the
immediate structure.
- Vastly simplified, using a busy looping IPI with interrupts disabled.
Does not protect against NMI nor MCE.
- Pack the __imv section. Use smallest types required for size (char).
- Use imv_* instead of immediate_*.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
CC: Andi Kleen <ak@....de>
CC: "H. Peter Anvin" <hpa@...or.com>
CC: Chuck Ebbert <cebbert@...hat.com>
CC: Christoph Hellwig <hch@...radead.org>
CC: Jeremy Fitzhardinge <jeremy@...p.org>
CC: Thomas Gleixner <tglx@...utronix.de>
CC: Ingo Molnar <mingo@...hat.com>
CC: Rusty Russell <rusty@...tcorp.com.au>
CC: Adrian Bunk <bunk@...sta.de>
CC: akpm@...l.org
---
arch/x86/Kconfig | 1
include/asm-x86/immediate.h | 77 ++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 78 insertions(+)
Index: linux-2.6-lttng/include/asm-x86/immediate.h
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6-lttng/include/asm-x86/immediate.h 2008-04-09 15:02:34.000000000 -0400
@@ -0,0 +1,67 @@
+#ifndef _ASM_X86_IMMEDIATE_H
+#define _ASM_X86_IMMEDIATE_H
+
+/*
+ * Immediate values. x86 architecture optimizations.
+ *
+ * (C) Copyright 2006 Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
+ *
+ * This file is released under the GPLv2.
+ * See the file COPYING for more details.
+ */
+
+#include <asm/asm.h>
+
+/**
+ * imv_read - read immediate variable
+ * @name: immediate value name
+ *
+ * Reads the value of @name.
+ * Optimized version of the immediate.
+ * Do not use in __init and __exit functions. Use _imv_read() instead.
+ * If size is bigger than the architecture long size, fall back on a memory
+ * read.
+ *
+ * Make sure to populate the initial static 64 bits opcode with a value
+ * what will generate an instruction with 8 bytes immediate value (not the REX.W
+ * prefixed one that loads a sign extended 32 bits immediate value in a r64
+ * register).
+ */
+#define imv_read(name) \
+ ({ \
+ __typeof__(name##__imv) value; \
+ BUILD_BUG_ON(sizeof(value) > 8); \
+ switch (sizeof(value)) { \
+ case 1: \
+ case 2: \
+ case 4: \
+ asm(".section __imv,\"a\",@progbits\n\t" \
+ _ASM_PTR "%c1, (3f)-%c2\n\t" \
+ ".byte %c2\n\t" \
+ ".previous\n\t" \
+ "mov $0,%0\n\t" \
+ "3:\n\t" \
+ : "=r" (value) \
+ : "i" (&name##__imv), \
+ "i" (sizeof(value))); \
+ break; \
+ case 8: \
+ if (sizeof(long) < 8) { \
+ value = name##__imv; \
+ break; \
+ } \
+ asm(".section __imv,\"a\",@progbits\n\t" \
+ _ASM_PTR "%c1, (3f)-%c2\n\t" \
+ ".byte %c2\n\t" \
+ ".previous\n\t" \
+ "mov $0xFEFEFEFE01010101,%0\n\t" \
+ "3:\n\t" \
+ : "=r" (value) \
+ : "i" (&name##__imv), \
+ "i" (sizeof(value))); \
+ break; \
+ }; \
+ value; \
+ })
+
+#endif /* _ASM_X86_IMMEDIATE_H */
Index: linux-2.6-lttng/arch/x86/Kconfig
===================================================================
--- linux-2.6-lttng.orig/arch/x86/Kconfig 2008-04-09 11:04:58.000000000 -0400
+++ linux-2.6-lttng/arch/x86/Kconfig 2008-04-09 15:00:01.000000000 -0400
@@ -23,6 +23,7 @@ config X86
select HAVE_KPROBES
select HAVE_KRETPROBES
select HAVE_KVM if ((X86_32 && !X86_VOYAGER && !X86_VISWS && !X86_NUMAQ) || X86_64)
+ select HAVE_IMMEDIATE
config GENERIC_LOCKBREAK
--
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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