From 2d7bc823503167276c6d3c40500c3055d4f38938 Mon Sep 17 00:00:00 2001
From: Ian Moffett <ian@osmora.org>
Date: Tue, 2 Jul 2024 21:19:49 -0400
Subject: kernel/amd64: Handle the user GS segment register

This commit introduces usage of swapgs to switch out the GS register
with the user GS register. An md_td_kick() function is also introduced
to start up user threads. The this_cpu() function uses the GS register
to read the current CPU structure using a new "self" field.

Signed-off-by: Ian Moffett <ian@osmora.org>
---
 sys/include/arch/amd64/cpu.h      |  1 +
 sys/include/arch/amd64/frameasm.h | 24 ++++++++++++++++++++----
 sys/include/sys/proc.h            |  2 ++
 3 files changed, 23 insertions(+), 4 deletions(-)

(limited to 'sys/include')

diff --git a/sys/include/arch/amd64/cpu.h b/sys/include/arch/amd64/cpu.h
index 16936e9..2ce363c 100644
--- a/sys/include/arch/amd64/cpu.h
+++ b/sys/include/arch/amd64/cpu.h
@@ -42,6 +42,7 @@ struct cpu_info {
     size_t lapic_tmr_freq;
     struct tss_entry *tss;
     struct proc *curtd;
+    struct cpu_info *self;
 };
 
 void cpu_startup(struct cpu_info *ci);
diff --git a/sys/include/arch/amd64/frameasm.h b/sys/include/arch/amd64/frameasm.h
index b8791ba..8983d36 100644
--- a/sys/include/arch/amd64/frameasm.h
+++ b/sys/include/arch/amd64/frameasm.h
@@ -106,11 +106,19 @@
  */
 #define INTRENTRY(ENTLABEL, HANDLER)    \
     ENTLABEL:                           \
-        push_trapframe $0             ; \
+        testq $0x3, 8(%rsp)           ; \
+        jz 1f                         ; \
+        lfence                        ; \
+        swapgs                        ; \
+    1:  push_trapframe $0             ; \
         mov %rsp, %rdi                ; \
         call HANDLER                  ; \
         pop_trapframe                 ; \
-        iretq
+        testq $0x3, 8(%rsp)           ; \
+        jz 2f                         ; \
+        lfence                        ; \
+        swapgs                        ; \
+    2:  iretq
 
 /*
  * Trap entry where an error code is on
@@ -118,10 +126,18 @@
  */
 #define TRAPENTRY(ENTLABEL, TRAPNO)    \
     ENTLABEL:                          \
-        push_trapframe_ec TRAPNO     ; \
+        testq $0x3, 8(%rsp)          ; \
+        jz 1f                        ; \
+        lfence                       ; \
+        swapgs                       ; \
+    1:  push_trapframe_ec TRAPNO     ; \
         mov %rsp, %rdi               ; \
         call trap_handler            ; \
         pop_trapframe_ec             ; \
-        iretq
+        testq $0x3, 8(%rsp)          ; \
+        jz 2f                        ; \
+        lfence                       ; \
+        swapgs                       ; \
+    2:  iretq
 
 #endif  /* !_MACHINE_FRAMEASM_H_ */
diff --git a/sys/include/sys/proc.h b/sys/include/sys/proc.h
index ba931f3..805c4a5 100644
--- a/sys/include/sys/proc.h
+++ b/sys/include/sys/proc.h
@@ -34,6 +34,7 @@
 #include <sys/spinlock.h>
 #include <sys/queue.h>
 #include <sys/param.h>
+#include <sys/cdefs.h>
 #if defined(_KERNEL)
 #include <machine/frame.h>
 #include <machine/pcb.h>
@@ -63,6 +64,7 @@ struct proc *this_td(void);
 int md_fork(struct proc *p, struct proc *parent, uintptr_t ip);
 
 void md_td_stackinit(struct proc *td, void *stack_top, struct exec_prog *prog);
+__dead void md_td_kick(struct proc *td);
 
 int fork1(struct proc *cur, int flags, void(*ip)(void), struct proc **newprocp);
 int exit1(struct proc *td);
-- 
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