kernel/x86: stores cpu number in TSC_AUX if rdtscp is available

On modern x86, one can use __rdtscp to get the current cpu in userland.

Change-Id: I1767e379606230a75e4622637c7a5aed9cdf9ab0
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2248
Reviewed-by: Adrien Destugues <[email protected]>

headers/private/kernel/arch/x86/arch_cpu.h

@@ -114,6 +114,7 @@
 #define IA32_MSR_FS_BASE				0xc0000100
 #define IA32_MSR_GS_BASE				0xc0000101
 #define IA32_MSR_KERNEL_GS_BASE			0xc0000102
+#define IA32_MSR_TSC_AUX				0xc0000103
 
 // K8 MSR registers
 #define K8_MSR_IPM						0xc0010055

src/system/kernel/arch/x86/arch_cpu.cpp

@@ -1145,6 +1145,12 @@ arch_cpu_init_percpu(kernel_args* args, int cpu)
 			gCpuIdleFunc = halt_idle;
 	}
 
+#ifdef __x86_64__
+	// if RDTSCP is available write cpu number in TSC_AUX
+	if (x86_check_feature(IA32_FEATURE_AMD_EXT_RDTSCP, FEATURE_EXT_AMD))
+		x86_write_msr(IA32_MSR_TSC_AUX, cpu);
+#endif
+
 	return __x86_patch_errata_percpu(cpu);
 }
 

src/tests/system/libroot/os/Jamfile

@@ -24,6 +24,10 @@ SimpleTest system_watching_test :
 	system_watching_test.cpp
 ;
 
+SimpleTest get_cpu_num_test :
+	get_cpu_num_test.cpp
+;
+
 # Tell Jam where to find these sources
 SEARCH on [ FGristFiles
 		driver_settings.cpp

src/tests/system/libroot/os/get_cpu_num_test.cpp

@@ -0,0 +1,56 @@
+/*
+ * Copyright 2020, Jérôme Duval, [email protected].
+ * Distributed under the terms of the MIT License.
+ */
+
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <OS.h>
+
+#include <x86intrin.h>
+
+extern const char* __progname;
+
+
+static void
+print_usage(bool error)
+{
+	fprintf(error ? stderr : stdout,
+		"Usage: %s\n",
+		__progname);
+}
+
+
+static void
+print_usage_and_exit(bool error)
+{
+	print_usage(error);
+	exit(error ? 1 : 0);
+}
+
+
+int
+main(int argc, const char* const* argv)
+{
+
+	if (argc > 2)
+		print_usage_and_exit(true);
+
+	if (argc > 1) {
+		const char* arg = argv[1];
+		if (strcmp(arg, "-h") == 0 || strcmp(arg, "--help") == 0)
+			print_usage_and_exit(false);
+	}
+
+#ifdef __x86_64__
+	uint32 cpuNum;
+	__rdtscp(&cpuNum);
+	printf("%" B_PRIu32 "\n", cpuNum);
+	return 0;
+#else
+	return 1;
+#endif
+}