sched: implement user-configurable fs and gs segment base addresses

arch/x86_64/thread.c

@@ -1,5 +1,7 @@
+#include <arch/msr.h>
 #include <kernel/machine/cpu.h>
 #include <kernel/machine/thread.h>
+#include <kernel/thread.h>
 
 #define MAX_REG_ARGS 6
 #define REG_ARG_0    rdi
@@ -77,3 +79,52 @@ extern kern_status_t ml_thread_prepare_user_context(
 
 	return KERN_OK;
 }
+
+kern_status_t ml_thread_config_get(
+	struct thread *thread,
+	kern_config_key_t key,
+	void *out,
+	size_t max)
+{
+	return KERN_OK;
+}
+
+kern_status_t ml_thread_config_set(
+	struct thread *thread,
+	kern_config_key_t key,
+	const void *ptr,
+	size_t len)
+{
+	switch (key) {
+	case THREAD_CFG_FSBASE:
+		if (len != sizeof(thread->tr_ml.tr_fsbase)) {
+			return KERN_INVALID_ARGUMENT;
+		}
+
+		thread->tr_ml.tr_fsbase = *(virt_addr_t *)ptr;
+		if (thread == current_thread()) {
+			wrmsr(MSR_FS_BASE, thread->tr_ml.tr_fsbase);
+		}
+
+		break;
+	case THREAD_CFG_GSBASE:
+		if (len != sizeof(thread->tr_ml.tr_gsbase)) {
+			return KERN_INVALID_ARGUMENT;
+		}
+
+		thread->tr_ml.tr_gsbase = *(virt_addr_t *)ptr;
+		if (thread == current_thread()) {
+			/* we're in the kernel right now, so the user and kernel
+			 * gs-base registers are swapped. when we return to
+			 * usermode, this value will be swapped back into
+			 * the user gs-base register */
+			wrmsr(MSR_KERNEL_GS_BASE, thread->tr_ml.tr_gsbase);
+		}
+
+		break;
+	default:
+		return KERN_INVALID_ARGUMENT;
+	}
+
+	return KERN_OK;
+}