MSR and syscall changes

- Moved MSR code to separate files with an enum class
- Implemented syscall_enable in C++ using new MSR calls

src/kernel/io.cpp

@@ -14,22 +14,6 @@ outb(uint16_t port, uint8_t val)
 	__asm__ __volatile__ ( "outb %0, %1" :: "a"(val), "Nd"(port) );
 }
 
-uint64_t
-rdmsr(uint64_t addr)
-{
-	uint32_t low, high;
-	__asm__ __volatile__ ("rdmsr" : "=a"(low), "=d"(high) : "c"(addr));
-	return (static_cast<uint64_t>(high) << 32) | low;
-}
-
-void
-wrmsr(uint64_t addr, uint64_t value)
-{
-	uint32_t low = value & 0xffffffff;
-	uint32_t high = value >> 32;
-	__asm__ __volatile__ ("wrmsr" :: "c"(addr), "a"(low), "d"(high));
-}
-
 void
 io_wait(unsigned times)
 {

src/kernel/io.h

@@ -14,16 +14,6 @@ uint8_t inb(uint16_t port);
 /// \arg val   The byte to write
 void outb(uint16_t port, uint8_t val);
 
-/// Read the value of a MSR
-/// \arg addr   The MSR address
-/// \returns    The current value of the MSR
-uint64_t rdmsr(uint64_t addr);
-
-/// Write to a MSR
-/// \arg addr   The MSR address
-/// \arg value  The value to write
-void wrmsr(uint64_t addr, uint64_t value);
-
 /// Pause briefly by doing IO to port 0x80
 /// \arg times  Number of times to delay by writing
 void io_wait(unsigned times = 1);

src/kernel/main.cpp

@@ -18,10 +18,10 @@
 #include "scheduler.h"
 #include "screen.h"
 #include "serial.h"
+#include "syscall.h"
 
 extern "C" {
 	void kernel_main(popcorn_data *header);
-	void syscall_enable();
 
 	void *__bss_start, *__bss_end;
 }

src/kernel/msr.cpp

@@ -0,0 +1,18 @@
+#include "msr.h"
+
+uint64_t
+rdmsr(msr addr)
+{
+	uint32_t low, high;
+	__asm__ __volatile__ ("rdmsr" : "=a"(low), "=d"(high) : "c"(addr));
+	return (static_cast<uint64_t>(high) << 32) | low;
+}
+
+void
+wrmsr(msr addr, uint64_t value)
+{
+	uint32_t low = value & 0xffffffff;
+	uint32_t high = value >> 32;
+	__asm__ __volatile__ ("wrmsr" :: "c"(addr), "a"(low), "d"(high));
+}
+

src/kernel/msr.h

@@ -0,0 +1,27 @@
+#pragma once
+/// \file msr.h
+/// Routines and definitions for dealing with Model-Specific Registers
+
+#include <stdint.h>
+
+enum class msr : uint32_t
+{
+	ia32_efer			= 0xc0000080,
+	ia32_star			= 0xc0000081,
+	ia32_lstar			= 0xc0000082,
+	ia32_fmask			= 0xc0000084,
+
+	ia32_gs_base		= 0xc0000101,
+	ia32_kernel_gs_base = 0xc0000102
+};
+
+/// Read the value of a MSR
+/// \arg addr   The MSR address
+/// \returns    The current value of the MSR
+uint64_t rdmsr(msr addr);
+
+/// Write to a MSR
+/// \arg addr   The MSR address
+/// \arg value  The value to write
+void wrmsr(msr addr, uint64_t value);
+

src/kernel/scheduler.cpp

@@ -5,6 +5,7 @@
 #include "interrupts.h"
 #include "io.h"
 #include "log.h"
+#include "msr.h"
 #include "page_manager.h"
 #include "scheduler.h"
 
@@ -194,12 +195,10 @@ scheduler::schedule(addr_t rsp0)
 	m_current = m_runlists[pri].pop_front();
 	rsp0 = m_current->rsp;
 
-	static const uint64_t ia32_gs_base = 0xc0000101;
-	static const uint64_t ia32_kernel_gs_base = 0xc0000102;
-
 	// Set rsp0 to after the end of the about-to-be-popped cpu state
 	tss_set_stack(0, rsp0 + sizeof(cpu_state));
-	wrmsr(ia32_gs_base, rsp0);
+	wrmsr(msr::ia32_kernel_gs_base, rsp0);
+	log::debug(logs::task, "Scheduler set kernel_gs_base to %016lx", rsp0);
 
 	// Swap page tables
 	page_table *pml4 = m_current->pml4;

src/kernel/syscall.cpp

@@ -1,11 +1,36 @@
 #include "console.h"
 #include "cpu.h"
 #include "debug.h"
+#include "msr.h"
 #include "scheduler.h"
 #include "syscall.h"
 
 extern "C" {
 	void _halt();
+	void syscall_handler_prelude();
+}
+
+void
+syscall_enable()
+{
+	// IA32_EFER - set bit 0, syscall enable
+	uint64_t efer = rdmsr(msr::ia32_efer);
+	wrmsr(msr::ia32_efer, efer|1);
+
+	// IA32_STAR - high 32 bits contain k+u CS
+	// Kernel CS: GDT[1] ring 0 bits[47:32]
+	//   User CS: GDT[3] ring 3 bits[63:48]
+	uint64_t star =
+		(((1ull << 3) | 0) << 32) |
+		(((3ull << 3) | 3) << 48);
+	wrmsr(msr::ia32_star, star);
+
+	// IA32_LSTAR - RIP for syscall
+	wrmsr(msr::ia32_lstar,
+		reinterpret_cast<addr_t>(&syscall_handler_prelude));
+
+	// IA32_FMASK - FLAGS mask inside syscall
+	wrmsr(msr::ia32_fmask, 0x200);
 }
 
 addr_t

src/kernel/syscall.h

@@ -3,6 +3,8 @@
 #include <stdint.h>
 #include "kutil/memory.h"
 
+struct cpu_state;
+
 enum class syscall : uint64_t
 {
 	noop,
@@ -13,6 +15,6 @@ enum class syscall : uint64_t
 	last_syscall
 };
 
-struct cpu_state;
+void syscall_enable();
 addr_t syscall_dispatch(addr_t, const cpu_state &);
 

src/kernel/syscall.s

@@ -1,35 +1,7 @@
 %include "push_all.inc"
 
-global syscall_enable
-syscall_enable:
-	; IA32_EFER - set bit 0, syscall enable
-	mov rcx, 0xc0000080
-	rdmsr
-	or rax, 0x1
-	wrmsr
-
-	; IA32_STAR - cs for syscall
-	mov rcx, 0xc0000081
-	mov rax, 0			; not used
-	mov rdx, 0x00180008	; GDT:3 (user code), GDT:1 (kernel code)
-	wrmsr
-
-	; IA32_LSTAR - RIP for syscall
-	mov rcx, 0xc0000082
-	lea rax, [rel syscall_handler_prelude]
-	mov rdx, rax
-	shr rdx, 32
-	wrmsr
-
-	; IA32_FMASK - FLAGS mask inside syscall
-	mov rcx, 0xc0000084
-	mov rax, 0x200
-	mov rdx, 0
-	wrmsr
-
-	ret
-
 extern syscall_handler
+global syscall_handler_prelude
 syscall_handler_prelude:
 	push 0		; ss, doesn't matter here
 	push rsp