From cce444f546a20374b81b3e04c9e2472ba98e9c41 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Thomas=20Lov=C3=A9n?= <thomasloven@gmail.com>
Date: Thu, 15 Mar 2018 12:58:03 +0100
Subject: [PATCH] Reference cpu specific information via gs segment

---
 src/kernel/cpu/cpu.c        | 11 ++++++++---
 src/kernel/cpu/gdt.c        |  2 +-
 src/kernel/cpu/isr_common.S | 14 ++++++++++++++
 src/kernel/cpu/registers.S  | 17 +++++++++++++++++
 src/kernel/include/cpu.h    |  6 +++++-
 5 files changed, 45 insertions(+), 5 deletions(-)

diff --git a/src/kernel/cpu/cpu.c b/src/kernel/cpu/cpu.c
index 86c36ae..d27cb27 100644
--- a/src/kernel/cpu/cpu.c
+++ b/src/kernel/cpu/cpu.c
@@ -1,15 +1,20 @@
 #include <cpu.h>
 #include <interrupts.h>
 #include <memory.h>
+#include <debug.h>
 
 void gdt_init(struct cpu *cpu);
 
-struct cpu *cpu;
+struct cpu __seg_gs *cpu = 0;
 
 void cpu_init()
 {
-  cpu = P2V(pmm_calloc());
+  struct cpu *c = P2V(pmm_calloc());
+  c->cpu = c;
+  write_msr(0xc0000102, (uint64_t)c);
+  asm("swapgs");
+
   interrupt_init();
-  gdt_init(cpu);
+  gdt_init(cpu->cpu);
 }
 
diff --git a/src/kernel/cpu/gdt.c b/src/kernel/cpu/gdt.c
index 8ffc369..08ad4df 100644
--- a/src/kernel/cpu/gdt.c
+++ b/src/kernel/cpu/gdt.c
@@ -77,6 +77,6 @@ void gdt_init(struct cpu *c)
 
 void interrupt_stack(void *rsp0)
 {
-  struct tss *tss = (void *)cpu->tss;
+  struct tss __seg_gs *tss = (void __seg_gs *)(cpu->tss);
   tss->rsp0 = (uint64_t)rsp0;
 }
diff --git a/src/kernel/cpu/isr_common.S b/src/kernel/cpu/isr_common.S
index e1b888a..1af1a7d 100644
--- a/src/kernel/cpu/isr_common.S
+++ b/src/kernel/cpu/isr_common.S
@@ -20,12 +20,26 @@ isr_common:
   push rcx
   push rbx
   push rax
+
+  mov rax, [rsp + 152]
+  and rax, (3<<12)
+  jz .kernel_interrupt
+  swapgs
+
+.kernel_interrupt:
   mov rdi, rsp
   call int_handler
 
   mov rdi, rax
 isr_return:
   mov rsp, rdi
+
+  mov rax, [rsp + 152]
+  and rax, (3<<12)
+  jz .kernel_return
+  swapgs
+
+.kernel_return:
   pop rax
   pop rbx
   pop rcx
diff --git a/src/kernel/cpu/registers.S b/src/kernel/cpu/registers.S
index f99166d..2f0c7ea 100644
--- a/src/kernel/cpu/registers.S
+++ b/src/kernel/cpu/registers.S
@@ -41,3 +41,20 @@ write_cr3:
 read_cr4:
   mov rax, cr4
   ret
+
+.global read_msr
+read_msr:
+  mov rcx, rdi
+  rdmsr
+  shl rdx, 32
+  add rax, rdx
+  ret
+
+.global write_msr
+write_msr:
+  mov rcx, rdi
+  mov rax, rsi
+  mov rdx, rsi
+  shr rdx, 32
+  wrmsr
+  ret
diff --git a/src/kernel/include/cpu.h b/src/kernel/include/cpu.h
index 80ef952..c34fdac 100644
--- a/src/kernel/include/cpu.h
+++ b/src/kernel/include/cpu.h
@@ -4,13 +4,14 @@
 
 struct cpu
 {
+  void *cpu;
   uint64_t gdt[6];
   uint8_t tss[104];
   struct process *proc;
   struct process *scheduler;
 };
 
-extern struct cpu *cpu;
+extern struct cpu __seg_gs *cpu;
 
 void cpu_init();
 
@@ -24,3 +25,6 @@ uint64_t read_cr2();
 uint64_t read_cr3();
 void write_cr3(uint64_t);
 uint64_t read_cr4();
+
+void write_msr(uint64_t reg, uint64_t value);
+uint64_t read_msr(uint64_t reg);