wip: LoongArch: use trampoline for exception handlers

Signed-off-by: Xi Ruoyao <xry111@xry111.site>

Author: xry111

arch/loongarch/kernel/genex.S

@@ -32,7 +32,7 @@ SYM_FUNC_START(__arch_cpu_idle)
 SYM_FUNC_END(__arch_cpu_idle)
 
 SYM_FUNC_START(handle_vint)
-	BACKUP_T0T1
+	# BACKUP_T0T1
 	SAVE_ALL
 	la.abs	t1, __arch_cpu_idle
 	LONG_L	t0, sp, PT_ERA
@@ -67,7 +67,7 @@ SYM_FUNC_END(except_vec_cex)
 	.macro	BUILD_HANDLER exception handler prep
 	.align	5
 	SYM_FUNC_START(handle_\exception)
-	BACKUP_T0T1
+	# BACKUP_T0T1
 	SAVE_ALL
 	build_prep_\prep
 	move	a0, sp
@@ -93,3 +93,12 @@ SYM_FUNC_START(handle_sys)
 	la.abs	t0, handle_syscall
 	jr	t0
 SYM_FUNC_END(handle_sys)
+
+SYM_FUNC_START(handler_trampoline)
+	csrwr	t0, EXCEPTION_KS0
+	csrwr	t1, EXCEPTION_KS1
+	pcaddi	t0, 0
+	ld.d	t0, t0, 16
+	jr	t0
+	nop
+SYM_FUNC_END(handler_trampoline)

arch/loongarch/kernel/traps.c

@@ -60,6 +60,7 @@ extern asmlinkage void handle_lasx(void);
 extern asmlinkage void handle_reserved(void);
 extern asmlinkage void handle_watch(void);
 extern asmlinkage void handle_vint(void);
+extern asmlinkage void handler_trampoline(void);
 
 static void show_backtrace(struct task_struct *task, const struct pt_regs *regs,
 			   const char *loglvl, bool user)
@@ -677,7 +678,8 @@ void per_cpu_trap_init(int cpu)
 /* Install CPU exception handler */
 void set_handler(unsigned long offset, void *addr, unsigned long size)
 {
-	memcpy((void *)(eentry + offset), addr, size);
+	memcpy((void *)(eentry + offset), &handler_trampoline, 24);
+	memcpy((void *)(eentry + offset + 24), &addr, 8);
 	local_flush_icache_range(eentry + offset, eentry + offset + size);
 }
 

arch/loongarch/mm/tlbex.S

@@ -27,7 +27,7 @@
 	tlb_do_page_fault 1
 
 SYM_FUNC_START(handle_tlb_protect)
-	BACKUP_T0T1
+	# BACKUP_T0T1
 	SAVE_ALL
 	move	a0, sp
 	move	a1, zero
@@ -39,8 +39,8 @@ SYM_FUNC_START(handle_tlb_protect)
 SYM_FUNC_END(handle_tlb_protect)
 
 SYM_FUNC_START(handle_tlb_load)
-	csrwr	t0, EXCEPTION_KS0
-	csrwr	t1, EXCEPTION_KS1
+	#csrwr	t0, EXCEPTION_KS0
+	#csrwr	t1, EXCEPTION_KS1
 	csrwr	ra, EXCEPTION_KS2
 
 	/*
@@ -202,8 +202,8 @@ nopage_tlb_load:
 SYM_FUNC_END(handle_tlb_load)
 
 SYM_FUNC_START(handle_tlb_store)
-	csrwr	t0, EXCEPTION_KS0
-	csrwr	t1, EXCEPTION_KS1
+	#csrwr	t0, EXCEPTION_KS0
+	#csrwr	t1, EXCEPTION_KS1
 	csrwr	ra, EXCEPTION_KS2
 
 	/*
@@ -370,8 +370,8 @@ nopage_tlb_store:
 SYM_FUNC_END(handle_tlb_store)
 
 SYM_FUNC_START(handle_tlb_modify)
-	csrwr	t0, EXCEPTION_KS0
-	csrwr	t1, EXCEPTION_KS1
+	#csrwr	t0, EXCEPTION_KS0
+	#csrwr	t1, EXCEPTION_KS1
 	csrwr	ra, EXCEPTION_KS2
 
 	/*