Messages in this thread Patch in this message | | | Date | Wed, 9 Apr 2008 16:21:06 -0400 | From | Mathieu Desnoyers <> | Subject | Re: [patch 13/17] Immediate Values - x86 Optimization (updated) |
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* H. Peter Anvin (hpa@zytor.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@polymtl.ca> CC: Andi Kleen <ak@muc.de> CC: "H. Peter Anvin" <hpa@zytor.com> CC: Chuck Ebbert <cebbert@redhat.com> CC: Christoph Hellwig <hch@infradead.org> CC: Jeremy Fitzhardinge <jeremy@goop.org> CC: Thomas Gleixner <tglx@linutronix.de> CC: Ingo Molnar <mingo@redhat.com> CC: Rusty Russell <rusty@rustcorp.com.au> CC: Adrian Bunk <bunk@stusta.de> CC: akpm@osdl.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@polymtl.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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