LoongArch: Make do_xyz() exception handlers more robust

Currently, interrupts need to be disabled before single-step mode is
set, it requires that CSR_PRMD_PIE be cleared in save_local_irqflag()
which is called by setup_singlestep(), this is reasonable.

But in the first kprobe breakpoint exception, if the irq is enabled at
the beginning of do_bp(), it will not be disabled at the end of do_bp()
due to the CSR_PRMD_PIE has been cleared in save_local_irqflag(). So for
this case, it may corrupt exception context when restoring the exception
after do_bp() in handle_bp(), this is not reasonable.

In order to restore exception safely in handle_bp(), it needs to ensure
the irq is disabled at the end of do_bp(), so just add a local variable
to record the original interrupt status in the parent context, then use
it as the check condition to enable and disable irq in do_bp().

While at it, do the similar thing for other do_xyz() exception handlers
to make them more robust.

Fixes: 6d4cc40 ("LoongArch: Add kprobes support")
Suggested-by: Jinyang He <hejinyang@loongson.cn>
Suggested-by: Huacai Chen <chenhuacai@loongson.cn>
Co-developed-by: Tianyang Zhang <zhangtianyang@loongson.cn>
Signed-off-by: Tianyang Zhang <zhangtianyang@loongson.cn>
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

Author: seehearfeel

arch/loongarch/kernel/traps.c

@@ -553,9 +553,10 @@ asmlinkage void noinstr do_ale(struct pt_regs *regs)
 	die_if_kernel("Kernel ale access", regs);
 	force_sig_fault(SIGBUS, BUS_ADRALN, (void __user *)regs->csr_badvaddr);
 #else
+	bool pie = regs_irqs_disabled(regs);
 	unsigned int *pc;
 
-	if (regs->csr_prmd & CSR_PRMD_PIE)
+	if (!pie)
 		local_irq_enable();
 
 	perf_sw_event(PERF_COUNT_SW_ALIGNMENT_FAULTS, 1, regs, regs->csr_badvaddr);
@@ -582,7 +583,7 @@ asmlinkage void noinstr do_ale(struct pt_regs *regs)
 	die_if_kernel("Kernel ale access", regs);
 	force_sig_fault(SIGBUS, BUS_ADRALN, (void __user *)regs->csr_badvaddr);
 out:
-	if (regs->csr_prmd & CSR_PRMD_PIE)
+	if (!pie)
 		local_irq_disable();
 #endif
 	irqentry_exit(regs, state);
@@ -621,12 +622,13 @@ static void bug_handler(struct pt_regs *regs)
 asmlinkage void noinstr do_bce(struct pt_regs *regs)
 {
 	bool user = user_mode(regs);
+	bool pie = regs_irqs_disabled(regs);
 	unsigned long era = exception_era(regs);
 	u64 badv = 0, lower = 0, upper = ULONG_MAX;
 	union loongarch_instruction insn;
 	irqentry_state_t state = irqentry_enter(regs);
 
-	if (regs->csr_prmd & CSR_PRMD_PIE)
+	if (!pie)
 		local_irq_enable();
 
 	current->thread.trap_nr = read_csr_excode();
@@ -692,7 +694,7 @@ asmlinkage void noinstr do_bce(struct pt_regs *regs)
 	force_sig_bnderr((void __user *)badv, (void __user *)lower, (void __user *)upper);
 
 out:
-	if (regs->csr_prmd & CSR_PRMD_PIE)
+	if (!pie)
 		local_irq_disable();
 
 	irqentry_exit(regs, state);
@@ -710,11 +712,12 @@ asmlinkage void noinstr do_bce(struct pt_regs *regs)
 asmlinkage void noinstr do_bp(struct pt_regs *regs)
 {
 	bool user = user_mode(regs);
+	bool pie = regs_irqs_disabled(regs);
 	unsigned int opcode, bcode;
 	unsigned long era = exception_era(regs);
 	irqentry_state_t state = irqentry_enter(regs);
 
-	if (regs->csr_prmd & CSR_PRMD_PIE)
+	if (!pie)
 		local_irq_enable();
 
 	if (__get_inst(&opcode, (u32 *)era, user))
@@ -780,7 +783,7 @@ asmlinkage void noinstr do_bp(struct pt_regs *regs)
 	}
 
 out:
-	if (regs->csr_prmd & CSR_PRMD_PIE)
+	if (!pie)
 		local_irq_disable();
 
 	irqentry_exit(regs, state);
@@ -1015,6 +1018,7 @@ static void init_restore_lbt(void)
 
 asmlinkage void noinstr do_lbt(struct pt_regs *regs)
 {
+	bool pie = regs_irqs_disabled(regs);
 	irqentry_state_t state = irqentry_enter(regs);
 
 	/*
@@ -1024,7 +1028,7 @@ asmlinkage void noinstr do_lbt(struct pt_regs *regs)
 	 * (including the user using 'MOVGR2GCSR' to turn on TM, which
 	 * will not trigger the BTE), we need to check PRMD first.
 	 */
-	if (regs->csr_prmd & CSR_PRMD_PIE)
+	if (!pie)
 		local_irq_enable();
 
 	if (!cpu_has_lbt) {
@@ -1038,7 +1042,7 @@ asmlinkage void noinstr do_lbt(struct pt_regs *regs)
 	preempt_enable();
 
 out:
-	if (regs->csr_prmd & CSR_PRMD_PIE)
+	if (!pie)
 		local_irq_disable();
 
 	irqentry_exit(regs, state);