btrfs-progs: add run-time CPU feature detection

Add support for run-time detection of CPU features on x86_64 to allow
selection of accelerated implementations of hash algorithms.

When possible use the compiler builtin (works on gcc and clang).
The SHA extensions can't be detected by __builtin_cpu_supports and the
__cpuid/__cpuidex macros are not consistently provided in all supported
gcc and clang versions. Copy the __cpuidex and call it manually for the
SHA extensions. Complete list https://en.wikipedia.org/wiki/CPUID .

Signed-off-by: David Sterba <dsterba@suse.com>

Makefile

@@ -172,6 +172,7 @@ objects = \
 	kernel-shared/uuid-tree.o	\
 	kernel-shared/volumes.o	\
 	kernel-shared/zoned.o	\
+	common/cpu-utils.o	\
 	common/device-scan.o	\
 	common/device-utils.o	\
 	common/extent-cache.o	\

common/cpu-utils.c

@@ -0,0 +1,114 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License v2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this program; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 021110-1307, USA.
+ */
+
+#include <stdio.h>
+#include <stdbool.h>
+#include "common/cpu-utils.h"
+
+unsigned long __cpu_flags = 0;
+unsigned long __cpu_flags_orig = 0;
+
+#ifdef __x86_64__
+/*
+ * Do manual cpuid as cpuid.h is not available for all versions.
+ *
+ * Plain cpuid(level) is __cpuidex(level, 0), otherwise look for the leaf/subleaf
+ * modes at https://en.wikipedia.org/wiki/CPUID or compilers' cpuid.h.
+ */
+
+#ifndef __cpuidex
+#define __cpuidex(leaf, subleaf, a, b, c, d)				\
+	__asm__ __volatile__ ("cpuid\n\t"				\
+			: "=a" (a), "=b" (b), "=c" (c), "=d" (d)	\
+			: "0" (leaf), "2" (subleaf))
+#endif
+
+#else
+
+#define __cpuidex(leaf, subleaf, a, b, c, d)				\
+	do {								\
+		a = 0;							\
+		b = 0;							\
+		c = 0;							\
+		d = 0;							\
+	} while(0)
+#endif
+
+#define FLAG(name)	if (__cpu_flags & CPU_FLAG_ ## name) printf(" " #name)
+void cpu_print_flags(void) {
+	printf("CPU flags: 0x%lx\n", __cpu_flags);
+	printf("CPU features:");
+	FLAG(SSE2);
+	FLAG(SSSE3);
+	FLAG(SSE41);
+	FLAG(SSE42);
+	FLAG(SHA);
+	FLAG(AVX);
+	FLAG(AVX2);
+	putchar(10);
+}
+#undef FLAG
+
+#ifdef __x86_64__
+
+void cpu_detect_flags(void)
+{
+	unsigned int a, b, c, d;
+
+	__builtin_cpu_init();
+	if (__builtin_cpu_supports("sse2"))
+		__cpu_flags |= CPU_FLAG_SSE2;
+	if (__builtin_cpu_supports("ssse3"))
+		__cpu_flags |= CPU_FLAG_SSSE3;
+	if (__builtin_cpu_supports("sse4.1"))
+		__cpu_flags |= CPU_FLAG_SSE41;
+	if (__builtin_cpu_supports("sse4.2"))
+		__cpu_flags |= CPU_FLAG_SSE42;
+	if (__builtin_cpu_supports("avx"))
+		__cpu_flags |= CPU_FLAG_AVX;
+	if (__builtin_cpu_supports("avx2"))
+		__cpu_flags |= CPU_FLAG_AVX2;
+
+	/* Flags unsupported by builtins */
+	__cpuidex(7, 0, a, b, c, d);
+	if (b & (1UL << 29))
+		__cpu_flags |= CPU_FLAG_SHA;
+
+	__cpu_flags_orig = __cpu_flags;
+}
+
+void cpu_set_level(unsigned long topbit)
+{
+	if (topbit)
+		__cpu_flags &= (topbit << 1) - 1;
+	else
+		__cpu_flags = 0;
+}
+
+void cpu_reset_level(void)
+{
+	__cpu_flags = __cpu_flags_orig;
+}
+
+#else
+
+void cpu_detect_flags() { }
+
+void cpu_set_level(unsigned long topbit) { }
+
+void cpu_reset_level(void) { }
+
+#endif

common/cpu-utils.h

@@ -0,0 +1,58 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License v2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this program; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 021110-1307, USA.
+ */
+
+/*
+ * Detect CPU feature bits at runtime (x86_64 only)
+ */
+
+#ifndef __CPU_UTILS_H__
+#define __CPU_UTILS_H__
+
+#include <stdbool.h>
+
+#define ENUM_CPU_BIT(name)                              \
+	__ ## name ## _BIT,                             \
+	name = (1U << __ ## name ## _BIT),              \
+	__ ## name ## _SEQ = __ ## name ## _BIT
+
+enum cpu_feature {
+	ENUM_CPU_BIT(CPU_FLAG_SSE2),
+	ENUM_CPU_BIT(CPU_FLAG_SSSE3),
+	ENUM_CPU_BIT(CPU_FLAG_SSE41),
+	ENUM_CPU_BIT(CPU_FLAG_SSE42),
+	ENUM_CPU_BIT(CPU_FLAG_SHA),
+	ENUM_CPU_BIT(CPU_FLAG_AVX),
+	ENUM_CPU_BIT(CPU_FLAG_AVX2),
+};
+
+#undef ENUM_CPU_BIT
+
+/* Private but in public header to allow inlining */
+extern unsigned long __cpu_flags;
+extern unsigned long __cpu_flags_orig;
+
+/* Public API */
+void cpu_detect_flags(void);
+void cpu_set_level(unsigned long topbit);
+void cpu_reset_level(void);
+void cpu_print_flags(void);
+
+static inline bool cpu_has_feature(enum cpu_feature f)
+{
+	return __cpu_flags & f;
+}
+
+#endif