arch/x86/entry/common.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * common.c - C code for kernel entry and exit
  * Copyright (c) 2015 Andrew Lutomirski
  *
  * Based on asm and ptrace code by many authors.  The code here originated
  * in ptrace.c and signal.c.
  */

 #include <linux/kernel.h>
 #include <linux/sched.h>
 #include <linux/sched/task_stack.h>
 #include <linux/mm.h>
 #include <linux/smp.h>
 #include <linux/errno.h>
 #include <linux/ptrace.h>
 #include <linux/tracehook.h>
 #include <linux/audit.h>
 #include <linux/seccomp.h>
 #include <linux/signal.h>
 #include <linux/export.h>
 #include <linux/context_tracking.h>
 #include <linux/user-return-notifier.h>
 #include <linux/nospec.h>
 #include <linux/uprobes.h>
 #include <linux/livepatch.h>
 #include <linux/syscalls.h>
 #include <linux/uaccess.h>

 #ifdef CONFIG_XEN_PV
 #include <xen/xen-ops.h>
 #include <xen/events.h>
 #endif

 #include <asm/desc.h>
 #include <asm/traps.h>
 #include <asm/vdso.h>
 #include <asm/cpufeature.h>
 #include <asm/fpu/api.h>
 #include <asm/nospec-branch.h>
 #include <asm/io_bitmap.h>
 #include <asm/syscall.h>
 #include <asm/irq_stack.h>

 #define CREATE_TRACE_POINTS
 #include <trace/events/syscalls.h>

 #ifdef CONFIG_CONTEXT_TRACKING
 /**
  * enter_from_user_mode - Establish state when coming from user mode
  *
  * Syscall entry disables interrupts, but user mode is traced as interrupts
  * enabled. Also with NO_HZ_FULL RCU might be idle.
  *
  * 1) Tell lockdep that interrupts are disabled
  * 2) Invoke context tracking if enabled to reactivate RCU
  * 3) Trace interrupts off state
  */
 static noinstr void enter_from_user_mode(void)
 {
 	enum ctx_state state = ct_state();

 	lockdep_hardirqs_off(CALLER_ADDR0);
 	user_exit_irqoff();

 	instrumentation_begin();
 	CT_WARN_ON(state != CONTEXT_USER);
 	trace_hardirqs_off_finish();
 	instrumentation_end();
 }
 #else
 static __always_inline void enter_from_user_mode(void)
 {
 	lockdep_hardirqs_off(CALLER_ADDR0);
 	instrumentation_begin();
 	trace_hardirqs_off_finish();
 	instrumentation_end();
 }
 #endif

 /**
  * exit_to_user_mode - Fixup state when exiting to user mode
  *
  * Syscall exit enables interrupts, but the kernel state is interrupts
  * disabled when this is invoked. Also tell RCU about it.
  *
  * 1) Trace interrupts on state
  * 2) Invoke context tracking if enabled to adjust RCU state
  * 3) Clear CPU buffers if CPU is affected by MDS and the migitation is on.
  * 4) Tell lockdep that interrupts are enabled
  */
 static __always_inline void exit_to_user_mode(void)
 {
 	instrumentation_begin();
 	trace_hardirqs_on_prepare();
 	lockdep_hardirqs_on_prepare(CALLER_ADDR0);
 	instrumentation_end();

 	user_enter_irqoff();
 	mds_user_clear_cpu_buffers();
 	lockdep_hardirqs_on(CALLER_ADDR0);
 }

 static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch)
 {
 #ifdef CONFIG_X86_64
 	if (arch == AUDIT_ARCH_X86_64) {
 		audit_syscall_entry(regs->orig_ax, regs->di,
 				    regs->si, regs->dx, regs->r10);
 	} else
 #endif
 	{
 		audit_syscall_entry(regs->orig_ax, regs->bx,
 				    regs->cx, regs->dx, regs->si);
 	}
 }

 /*
  * Returns the syscall nr to run (which should match regs->orig_ax) or -1
  * to skip the syscall.
  */
 static long syscall_trace_enter(struct pt_regs *regs)
 {
 	u32 arch = in_ia32_syscall() ? AUDIT_ARCH_I386 : AUDIT_ARCH_X86_64;

 	struct thread_info *ti = current_thread_info();
 	unsigned long ret = 0;
 	u32 work;

 	if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
 		BUG_ON(regs != task_pt_regs(current));

 	work = READ_ONCE(ti->flags);

 	if (work & (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_EMU)) {
 		ret = tracehook_report_syscall_entry(regs);
 		if (ret || (work & _TIF_SYSCALL_EMU))
 			return -1L;
 	}

 #ifdef CONFIG_SECCOMP
 	/*
 	 * Do seccomp after ptrace, to catch any tracer changes.
 	 */
 	if (work & _TIF_SECCOMP) {
 		struct seccomp_data sd;

 		sd.arch = arch;
 		sd.nr = regs->orig_ax;
 		sd.instruction_pointer = regs->ip;
 #ifdef CONFIG_X86_64
 		if (arch == AUDIT_ARCH_X86_64) {
 			sd.args[0] = regs->di;
 			sd.args[1] = regs->si;
 			sd.args[2] = regs->dx;
 			sd.args[3] = regs->r10;
 			sd.args[4] = regs->r8;
 			sd.args[5] = regs->r9;
 		} else
 #endif
 		{
 			sd.args[0] = regs->bx;
 			sd.args[1] = regs->cx;
 			sd.args[2] = regs->dx;
 			sd.args[3] = regs->si;
 			sd.args[4] = regs->di;
 			sd.args[5] = regs->bp;
 		}

 		ret = __secure_computing(&sd);
 		if (ret == -1)
 			return ret;
 	}
 #endif

 	if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
 		trace_sys_enter(regs, regs->orig_ax);

 	do_audit_syscall_entry(regs, arch);

 	return ret ?: regs->orig_ax;
 }

 #define EXIT_TO_USERMODE_LOOP_FLAGS				\
 	(_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE |	\
 	 _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY | _TIF_PATCH_PENDING)

 static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
 {
 	/*
 	 * In order to return to user mode, we need to have IRQs off with
 	 * none of EXIT_TO_USERMODE_LOOP_FLAGS set.  Several of these flags
 	 * can be set at any time on preemptible kernels if we have IRQs on,
 	 * so we need to loop.  Disabling preemption wouldn't help: doing the
 	 * work to clear some of the flags can sleep.
 	 */
 	while (true) {
 		/* We have work to do. */
 		local_irq_enable();

 		if (cached_flags & _TIF_NEED_RESCHED)
 			schedule();

 		if (cached_flags & _TIF_UPROBE)
 			uprobe_notify_resume(regs);

 		if (cached_flags & _TIF_PATCH_PENDING)
 			klp_update_patch_state(current);

 		/* deal with pending signal delivery */
 		if (cached_flags & _TIF_SIGPENDING)
 			do_signal(regs);

 		if (cached_flags & _TIF_NOTIFY_RESUME) {
 			clear_thread_flag(TIF_NOTIFY_RESUME);
 			tracehook_notify_resume(regs);
 			rseq_handle_notify_resume(NULL, regs);
 		}

 		if (cached_flags & _TIF_USER_RETURN_NOTIFY)
 			fire_user_return_notifiers();

 		/* Disable IRQs and retry */
 		local_irq_disable();

 		cached_flags = READ_ONCE(current_thread_info()->flags);

 		if (!(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
 			break;
 	}
 }

 static void __prepare_exit_to_usermode(struct pt_regs *regs)
 {
 	struct thread_info *ti = current_thread_info();
 	u32 cached_flags;

 	addr_limit_user_check();

 	lockdep_assert_irqs_disabled();
 	lockdep_sys_exit();

 	cached_flags = READ_ONCE(ti->flags);

 	if (unlikely(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
 		exit_to_usermode_loop(regs, cached_flags);

 	/* Reload ti->flags; we may have rescheduled above. */
 	cached_flags = READ_ONCE(ti->flags);

 	if (unlikely(cached_flags & _TIF_IO_BITMAP))
 		tss_update_io_bitmap();

 	fpregs_assert_state_consistent();
 	if (unlikely(cached_flags & _TIF_NEED_FPU_LOAD))
 		switch_fpu_return();

 #ifdef CONFIG_COMPAT
 	/*
 	 * Compat syscalls set TS_COMPAT.  Make sure we clear it before
 	 * returning to user mode.  We need to clear it *after* signal
 	 * handling, because syscall restart has a fixup for compat
 	 * syscalls.  The fixup is exercised by the ptrace_syscall_32
 	 * selftest.
 	 *
 	 * We also need to clear TS_REGS_POKED_I386: the 32-bit tracer
 	 * special case only applies after poking regs and before the
 	 * very next return to user mode.
 	 */
 	ti->status &= ~(TS_COMPAT|TS_I386_REGS_POKED);
 #endif
 }

 __visible noinstr void prepare_exit_to_usermode(struct pt_regs *regs)
 {
 	instrumentation_begin();
 	__prepare_exit_to_usermode(regs);
 	instrumentation_end();
 	exit_to_user_mode();
 }

 #define SYSCALL_EXIT_WORK_FLAGS				\
 	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT |	\
 	 _TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT)

 static void syscall_slow_exit_work(struct pt_regs *regs, u32 cached_flags)
 {
 	bool step;

 	audit_syscall_exit(regs);

 	if (cached_flags & _TIF_SYSCALL_TRACEPOINT)
 		trace_sys_exit(regs, regs->ax);

 	/*
 	 * If TIF_SYSCALL_EMU is set, we only get here because of
 	 * TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP).
 	 * We already reported this syscall instruction in
 	 * syscall_trace_enter().
 	 */
 	step = unlikely(
 		(cached_flags & (_TIF_SINGLESTEP | _TIF_SYSCALL_EMU))
 		== _TIF_SINGLESTEP);
 	if (step || cached_flags & _TIF_SYSCALL_TRACE)
 		tracehook_report_syscall_exit(regs, step);
 }

 static void __syscall_return_slowpath(struct pt_regs *regs)
 {
 	struct thread_info *ti = current_thread_info();
 	u32 cached_flags = READ_ONCE(ti->flags);

 	CT_WARN_ON(ct_state() != CONTEXT_KERNEL);

 	if (IS_ENABLED(CONFIG_PROVE_LOCKING) &&
 	    WARN(irqs_disabled(), "syscall %ld left IRQs disabled", regs->orig_ax))
 		local_irq_enable();

 	rseq_syscall(regs);

 	/*
 	 * First do one-time work.  If these work items are enabled, we
 	 * want to run them exactly once per syscall exit with IRQs on.
 	 */
 	if (unlikely(cached_flags & SYSCALL_EXIT_WORK_FLAGS))
 		syscall_slow_exit_work(regs, cached_flags);

 	local_irq_disable();
 	__prepare_exit_to_usermode(regs);
 }

 /*
  * Called with IRQs on and fully valid regs.  Returns with IRQs off in a
  * state such that we can immediately switch to user mode.
  */
 __visible noinstr void syscall_return_slowpath(struct pt_regs *regs)
 {
 	instrumentation_begin();
 	__syscall_return_slowpath(regs);
 	instrumentation_end();
 	exit_to_user_mode();
 }

 #ifdef CONFIG_X86_64
 __visible noinstr void do_syscall_64(unsigned long nr, struct pt_regs *regs)
 {
 	struct thread_info *ti;

 	enter_from_user_mode();
 	instrumentation_begin();

 	local_irq_enable();
 	ti = current_thread_info();
 	if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY)
 		nr = syscall_trace_enter(regs);

 	if (likely(nr < NR_syscalls)) {
 		nr = array_index_nospec(nr, NR_syscalls);
 		regs->ax = sys_call_table[nr](regs);
 #ifdef CONFIG_X86_X32_ABI
 	} else if (likely((nr & __X32_SYSCALL_BIT) &&
 			  (nr & ~__X32_SYSCALL_BIT) < X32_NR_syscalls)) {
 		nr = array_index_nospec(nr & ~__X32_SYSCALL_BIT,
 					X32_NR_syscalls);
 		regs->ax = x32_sys_call_table[nr](regs);
 #endif
 	}
 	__syscall_return_slowpath(regs);

 	instrumentation_end();
 	exit_to_user_mode();
 }
 #endif

 #if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
 /*
  * Does a 32-bit syscall.  Called with IRQs on in CONTEXT_KERNEL.  Does
  * all entry and exit work and returns with IRQs off.  This function is
  * extremely hot in workloads that use it, and it's usually called from
  * do_fast_syscall_32, so forcibly inline it to improve performance.
  */
 static void do_syscall_32_irqs_on(struct pt_regs *regs)
 {
 	struct thread_info *ti = current_thread_info();
 	unsigned int nr = (unsigned int)regs->orig_ax;

 #ifdef CONFIG_IA32_EMULATION
 	ti->status |= TS_COMPAT;
 #endif

 	if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY) {
 		/*
 		 * Subtlety here: if ptrace pokes something larger than
 		 * 2^32-1 into orig_ax, this truncates it.  This may or
 		 * may not be necessary, but it matches the old asm
 		 * behavior.
 		 */
 		nr = syscall_trace_enter(regs);
 	}

 	if (likely(nr < IA32_NR_syscalls)) {
 		nr = array_index_nospec(nr, IA32_NR_syscalls);
 		regs->ax = ia32_sys_call_table[nr](regs);
 	}

 	__syscall_return_slowpath(regs);
 }

 /* Handles int $0x80 */
 __visible noinstr void do_int80_syscall_32(struct pt_regs *regs)
 {
 	enter_from_user_mode();
 	instrumentation_begin();

 	local_irq_enable();
 	do_syscall_32_irqs_on(regs);

 	instrumentation_end();
 	exit_to_user_mode();
 }

 static bool __do_fast_syscall_32(struct pt_regs *regs)
 {
 	int res;

 	/* Fetch EBP from where the vDSO stashed it. */
 	if (IS_ENABLED(CONFIG_X86_64)) {
 		/*
 		 * Micro-optimization: the pointer we're following is
 		 * explicitly 32 bits, so it can't be out of range.
 		 */
 		res = __get_user(*(u32 *)&regs->bp,
 			 (u32 __user __force *)(unsigned long)(u32)regs->sp);
 	} else {
 		res = get_user(*(u32 *)&regs->bp,
 		       (u32 __user __force *)(unsigned long)(u32)regs->sp);
 	}

 	if (res) {
 		/* User code screwed up. */
 		regs->ax = -EFAULT;
 		local_irq_disable();
 		__prepare_exit_to_usermode(regs);
 		return false;
 	}

 	/* Now this is just like a normal syscall. */
 	do_syscall_32_irqs_on(regs);
 	return true;
 }

 /* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */
 __visible noinstr long do_fast_syscall_32(struct pt_regs *regs)
 {
 	/*
 	 * Called using the internal vDSO SYSENTER/SYSCALL32 calling
 	 * convention.  Adjust regs so it looks like we entered using int80.
 	 */
 	unsigned long landing_pad = (unsigned long)current->mm->context.vdso +
 					vdso_image_32.sym_int80_landing_pad;
 	bool success;

 	/*
 	 * SYSENTER loses EIP, and even SYSCALL32 needs us to skip forward
 	 * so that 'regs->ip -= 2' lands back on an int $0x80 instruction.
 	 * Fix it up.
 	 */
 	regs->ip = landing_pad;

 	enter_from_user_mode();
 	instrumentation_begin();

 	local_irq_enable();
 	success = __do_fast_syscall_32(regs);

 	instrumentation_end();
 	exit_to_user_mode();

 	/* If it failed, keep it simple: use IRET. */
 	if (!success)
 		return 0;

 #ifdef CONFIG_X86_64
 	/*
 	 * Opportunistic SYSRETL: if possible, try to return using SYSRETL.
 	 * SYSRETL is available on all 64-bit CPUs, so we don't need to
 	 * bother with SYSEXIT.
 	 *
 	 * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
 	 * because the ECX fixup above will ensure that this is essentially
 	 * never the case.
 	 */
 	return regs->cs == __USER32_CS && regs->ss == __USER_DS &&
 		regs->ip == landing_pad &&
 		(regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF)) == 0;
 #else
 	/*
 	 * Opportunistic SYSEXIT: if possible, try to return using SYSEXIT.
 	 *
 	 * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
 	 * because the ECX fixup above will ensure that this is essentially
 	 * never the case.
 	 *
 	 * We don't allow syscalls at all from VM86 mode, but we still
 	 * need to check VM, because we might be returning from sys_vm86.
 	 */
 	return static_cpu_has(X86_FEATURE_SEP) &&
 		regs->cs == __USER_CS && regs->ss == __USER_DS &&
 		regs->ip == landing_pad &&
 		(regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF | X86_EFLAGS_VM)) == 0;
 #endif
 }
 #endif

 SYSCALL_DEFINE0(ni_syscall)
 {
 	return -ENOSYS;
 }

 /**
  * idtentry_enter_cond_rcu - Handle state tracking on idtentry with conditional
  *			     RCU handling
  * @regs:	Pointer to pt_regs of interrupted context
  *
  * Invokes:
  *  - lockdep irqflag state tracking as low level ASM entry disabled
  *    interrupts.
  *
  *  - Context tracking if the exception hit user mode.
  *
  *  - The hardirq tracer to keep the state consistent as low level ASM
  *    entry disabled interrupts.
  *
  * For kernel mode entries RCU handling is done conditional. If RCU is
  * watching then the only RCU requirement is to check whether the tick has
  * to be restarted. If RCU is not watching then rcu_irq_enter() has to be
  * invoked on entry and rcu_irq_exit() on exit.
  *
  * Avoiding the rcu_irq_enter/exit() calls is an optimization but also
  * solves the problem of kernel mode pagefaults which can schedule, which
  * is not possible after invoking rcu_irq_enter() without undoing it.
  *
  * For user mode entries enter_from_user_mode() must be invoked to
  * establish the proper context for NOHZ_FULL. Otherwise scheduling on exit
  * would not be possible.
  *
  * Returns: True if RCU has been adjusted on a kernel entry
  *	    False otherwise
  *
  * The return value must be fed into the rcu_exit argument of
  * idtentry_exit_cond_rcu().
  */
 bool noinstr idtentry_enter_cond_rcu(struct pt_regs *regs)
 {
 	if (user_mode(regs)) {
 		enter_from_user_mode();
 		return false;
 	}

 	/*
 	 * If this entry hit the idle task invoke rcu_irq_enter() whether
 	 * RCU is watching or not.
 	 *
 	 * Interupts can nest when the first interrupt invokes softirq
 	 * processing on return which enables interrupts.
 	 *
 	 * Scheduler ticks in the idle task can mark quiescent state and
 	 * terminate a grace period, if and only if the timer interrupt is
 	 * not nested into another interrupt.
 	 *
 	 * Checking for __rcu_is_watching() here would prevent the nesting
 	 * interrupt to invoke rcu_irq_enter(). If that nested interrupt is
 	 * the tick then rcu_flavor_sched_clock_irq() would wrongfully
 	 * assume that it is the first interupt and eventually claim
 	 * quiescient state and end grace periods prematurely.
 	 *
 	 * Unconditionally invoke rcu_irq_enter() so RCU state stays
 	 * consistent.
 	 *
 	 * TINY_RCU does not support EQS, so let the compiler eliminate
 	 * this part when enabled.
 	 */
 	if (!IS_ENABLED(CONFIG_TINY_RCU) && is_idle_task(current)) {
 		/*
 		 * If RCU is not watching then the same careful
 		 * sequence vs. lockdep and tracing is required
 		 * as in enter_from_user_mode().
 		 */
 		lockdep_hardirqs_off(CALLER_ADDR0);
 		rcu_irq_enter();
 		instrumentation_begin();
 		trace_hardirqs_off_finish();
 		instrumentation_end();

 		return true;
 	}

 	/*
 	 * If RCU is watching then RCU only wants to check whether it needs
 	 * to restart the tick in NOHZ mode. rcu_irq_enter_check_tick()
 	 * already contains a warning when RCU is not watching, so no point
 	 * in having another one here.
 	 */
 	instrumentation_begin();
 	rcu_irq_enter_check_tick();
 	/* Use the combo lockdep/tracing function */
 	trace_hardirqs_off();
 	instrumentation_end();

 	return false;
 }

 static void idtentry_exit_cond_resched(struct pt_regs *regs, bool may_sched)
 {
 	if (may_sched && !preempt_count()) {
 		/* Sanity check RCU and thread stack */
 		rcu_irq_exit_check_preempt();
 		if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
 			WARN_ON_ONCE(!on_thread_stack());
 		if (need_resched())
 			preempt_schedule_irq();
 	}
 	/* Covers both tracing and lockdep */
 	trace_hardirqs_on();
 }

 /**
  * idtentry_exit_cond_rcu - Handle return from exception with conditional RCU
  *			    handling
  * @regs:	Pointer to pt_regs (exception entry regs)
  * @rcu_exit:	Invoke rcu_irq_exit() if true
  *
  * Depending on the return target (kernel/user) this runs the necessary
  * preemption and work checks if possible and reguired and returns to
  * the caller with interrupts disabled and no further work pending.
  *
  * This is the last action before returning to the low level ASM code which
  * just needs to return to the appropriate context.
  *
  * Counterpart to idtentry_enter_cond_rcu(). The return value of the entry
  * function must be fed into the @rcu_exit argument.
  */
 void noinstr idtentry_exit_cond_rcu(struct pt_regs *regs, bool rcu_exit)
 {
 	lockdep_assert_irqs_disabled();

 	/* Check whether this returns to user mode */
 	if (user_mode(regs)) {
 		prepare_exit_to_usermode(regs);
 	} else if (regs->flags & X86_EFLAGS_IF) {
 		/*
 		 * If RCU was not watching on entry this needs to be done
 		 * carefully and needs the same ordering of lockdep/tracing
 		 * and RCU as the return to user mode path.
 		 */
 		if (rcu_exit) {
 			instrumentation_begin();
 			/* Tell the tracer that IRET will enable interrupts */
 			trace_hardirqs_on_prepare();
 			lockdep_hardirqs_on_prepare(CALLER_ADDR0);
 			instrumentation_end();
 			rcu_irq_exit();
 			lockdep_hardirqs_on(CALLER_ADDR0);
 			return;
 		}

 		instrumentation_begin();
 		idtentry_exit_cond_resched(regs, IS_ENABLED(CONFIG_PREEMPTION));
 		instrumentation_end();
 	} else {
 		/*
 		 * IRQ flags state is correct already. Just tell RCU if it
 		 * was not watching on entry.
 		 */
 		if (rcu_exit)
 			rcu_irq_exit();
 	}
 }

 /**
  * idtentry_enter_user - Handle state tracking on idtentry from user mode
  * @regs:	Pointer to pt_regs of interrupted context
  *
  * Invokes enter_from_user_mode() to establish the proper context for
  * NOHZ_FULL. Otherwise scheduling on exit would not be possible.
  */
 void noinstr idtentry_enter_user(struct pt_regs *regs)
 {
 	enter_from_user_mode();
 }

 /**
  * idtentry_exit_user - Handle return from exception to user mode
  * @regs:	Pointer to pt_regs (exception entry regs)
  *
  * Runs the necessary preemption and work checks and returns to the caller
  * with interrupts disabled and no further work pending.
  *
  * This is the last action before returning to the low level ASM code which
  * just needs to return to the appropriate context.
  *
  * Counterpart to idtentry_enter_user().
  */
 void noinstr idtentry_exit_user(struct pt_regs *regs)
 {
 	lockdep_assert_irqs_disabled();

 	prepare_exit_to_usermode(regs);
 }

 #ifdef CONFIG_XEN_PV
 #ifndef CONFIG_PREEMPTION
 /*
  * Some hypercalls issued by the toolstack can take many 10s of
  * seconds. Allow tasks running hypercalls via the privcmd driver to
  * be voluntarily preempted even if full kernel preemption is
  * disabled.
  *
  * Such preemptible hypercalls are bracketed by
  * xen_preemptible_hcall_begin() and xen_preemptible_hcall_end()
  * calls.
  */
 DEFINE_PER_CPU(bool, xen_in_preemptible_hcall);
 EXPORT_SYMBOL_GPL(xen_in_preemptible_hcall);

 /*
  * In case of scheduling the flag must be cleared and restored after
  * returning from schedule as the task might move to a different CPU.
  */
 static __always_inline bool get_and_clear_inhcall(void)
 {
 	bool inhcall = __this_cpu_read(xen_in_preemptible_hcall);

 	__this_cpu_write(xen_in_preemptible_hcall, false);
 	return inhcall;
 }

 static __always_inline void restore_inhcall(bool inhcall)
 {
 	__this_cpu_write(xen_in_preemptible_hcall, inhcall);
 }
 #else
 static __always_inline bool get_and_clear_inhcall(void) { return false; }
 static __always_inline void restore_inhcall(bool inhcall) { }
 #endif

 static void __xen_pv_evtchn_do_upcall(void)
 {
 	irq_enter_rcu();
 	inc_irq_stat(irq_hv_callback_count);

 	xen_hvm_evtchn_do_upcall();

 	irq_exit_rcu();
 }

 __visible noinstr void xen_pv_evtchn_do_upcall(struct pt_regs *regs)
 {
 	struct pt_regs *old_regs;
 	bool inhcall, rcu_exit;

 	rcu_exit = idtentry_enter_cond_rcu(regs);
 	old_regs = set_irq_regs(regs);

 	instrumentation_begin();
 	run_on_irqstack_cond(__xen_pv_evtchn_do_upcall, NULL, regs);
 	instrumentation_begin();

 	set_irq_regs(old_regs);

 	inhcall = get_and_clear_inhcall();
 	if (inhcall && !WARN_ON_ONCE(rcu_exit)) {
 		instrumentation_begin();
 		idtentry_exit_cond_resched(regs, true);
 		instrumentation_end();
 		restore_inhcall(inhcall);
 	} else {
 		idtentry_exit_cond_rcu(regs, rcu_exit);
 	}
 }
 #endif /* CONFIG_XEN_PV */
	// SPDX-License-Identifier: GPL-2.0-only
	/*
	* common.c - C code for kernel entry and exit
	* Copyright (c) 2015 Andrew Lutomirski
	*
	* Based on asm and ptrace code by many authors. The code here originated
	* in ptrace.c and signal.c.
	*/

	#include <linux/kernel.h>
	#include <linux/sched.h>
	#include <linux/sched/task_stack.h>
	#include <linux/mm.h>
	#include <linux/smp.h>
	#include <linux/errno.h>
	#include <linux/ptrace.h>
	#include <linux/tracehook.h>
	#include <linux/audit.h>
	#include <linux/seccomp.h>
	#include <linux/signal.h>
	#include <linux/export.h>
	#include <linux/context_tracking.h>
	#include <linux/user-return-notifier.h>
	#include <linux/nospec.h>
	#include <linux/uprobes.h>
	#include <linux/livepatch.h>
	#include <linux/syscalls.h>
	#include <linux/uaccess.h>

	#ifdef CONFIG_XEN_PV
	#include <xen/xen-ops.h>
	#include <xen/events.h>
	#endif

	#include <asm/desc.h>
	#include <asm/traps.h>
	#include <asm/vdso.h>
	#include <asm/cpufeature.h>
	#include <asm/fpu/api.h>
	#include <asm/nospec-branch.h>
	#include <asm/io_bitmap.h>
	#include <asm/syscall.h>
	#include <asm/irq_stack.h>

	#define CREATE_TRACE_POINTS
	#include <trace/events/syscalls.h>

	#ifdef CONFIG_CONTEXT_TRACKING
	/**
	* enter_from_user_mode - Establish state when coming from user mode
	*
	* Syscall entry disables interrupts, but user mode is traced as interrupts
	* enabled. Also with NO_HZ_FULL RCU might be idle.
	*
	* 1) Tell lockdep that interrupts are disabled
	* 2) Invoke context tracking if enabled to reactivate RCU
	* 3) Trace interrupts off state
	*/
	static noinstr void enter_from_user_mode(void)
	{
	enum ctx_state state = ct_state();

	lockdep_hardirqs_off(CALLER_ADDR0);
	user_exit_irqoff();

	instrumentation_begin();
	CT_WARN_ON(state != CONTEXT_USER);
	trace_hardirqs_off_finish();
	instrumentation_end();
	}
	#else
	static __always_inline void enter_from_user_mode(void)
	{
	lockdep_hardirqs_off(CALLER_ADDR0);
	instrumentation_begin();
	trace_hardirqs_off_finish();
	instrumentation_end();
	}
	#endif

	/**
	* exit_to_user_mode - Fixup state when exiting to user mode
	*
	* Syscall exit enables interrupts, but the kernel state is interrupts
	* disabled when this is invoked. Also tell RCU about it.
	*
	* 1) Trace interrupts on state
	* 2) Invoke context tracking if enabled to adjust RCU state
	* 3) Clear CPU buffers if CPU is affected by MDS and the migitation is on.
	* 4) Tell lockdep that interrupts are enabled
	*/
	static __always_inline void exit_to_user_mode(void)
	{
	instrumentation_begin();
	trace_hardirqs_on_prepare();
	lockdep_hardirqs_on_prepare(CALLER_ADDR0);
	instrumentation_end();

	user_enter_irqoff();
	mds_user_clear_cpu_buffers();
	lockdep_hardirqs_on(CALLER_ADDR0);
	}

	static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch)
	{
	#ifdef CONFIG_X86_64
	if (arch == AUDIT_ARCH_X86_64) {
	audit_syscall_entry(regs->orig_ax, regs->di,
	regs->si, regs->dx, regs->r10);
	} else
	#endif
	{
	audit_syscall_entry(regs->orig_ax, regs->bx,
	regs->cx, regs->dx, regs->si);
	}
	}

	/*
	* Returns the syscall nr to run (which should match regs->orig_ax) or -1
	* to skip the syscall.
	*/
	static long syscall_trace_enter(struct pt_regs *regs)
	{
	u32 arch = in_ia32_syscall() ? AUDIT_ARCH_I386 : AUDIT_ARCH_X86_64;

	struct thread_info *ti = current_thread_info();
	unsigned long ret = 0;
	u32 work;

	if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
	BUG_ON(regs != task_pt_regs(current));

	work = READ_ONCE(ti->flags);

	if (work & (_TIF_SYSCALL_TRACE \| _TIF_SYSCALL_EMU)) {
	ret = tracehook_report_syscall_entry(regs);
	if (ret \|\| (work & _TIF_SYSCALL_EMU))
	return -1L;
	}

	#ifdef CONFIG_SECCOMP
	/*
	* Do seccomp after ptrace, to catch any tracer changes.
	*/
	if (work & _TIF_SECCOMP) {
	struct seccomp_data sd;

	sd.arch = arch;
	sd.nr = regs->orig_ax;
	sd.instruction_pointer = regs->ip;
	#ifdef CONFIG_X86_64
	if (arch == AUDIT_ARCH_X86_64) {
	sd.args[0] = regs->di;
	sd.args[1] = regs->si;
	sd.args[2] = regs->dx;
	sd.args[3] = regs->r10;
	sd.args[4] = regs->r8;
	sd.args[5] = regs->r9;
	} else
	#endif
	{
	sd.args[0] = regs->bx;
	sd.args[1] = regs->cx;
	sd.args[2] = regs->dx;
	sd.args[3] = regs->si;
	sd.args[4] = regs->di;
	sd.args[5] = regs->bp;
	}

	ret = __secure_computing(&sd);
	if (ret == -1)
	return ret;
	}
	#endif

	if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
	trace_sys_enter(regs, regs->orig_ax);

	do_audit_syscall_entry(regs, arch);

	return ret ?: regs->orig_ax;
	}

	#define EXIT_TO_USERMODE_LOOP_FLAGS \
	(_TIF_SIGPENDING \| _TIF_NOTIFY_RESUME \| _TIF_UPROBE \| \
	_TIF_NEED_RESCHED \| _TIF_USER_RETURN_NOTIFY \| _TIF_PATCH_PENDING)

	static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
	{
	/*
	* In order to return to user mode, we need to have IRQs off with
	* none of EXIT_TO_USERMODE_LOOP_FLAGS set. Several of these flags
	* can be set at any time on preemptible kernels if we have IRQs on,
	* so we need to loop. Disabling preemption wouldn't help: doing the
	* work to clear some of the flags can sleep.
	*/
	while (true) {
	/* We have work to do. */
	local_irq_enable();

	if (cached_flags & _TIF_NEED_RESCHED)
	schedule();

	if (cached_flags & _TIF_UPROBE)
	uprobe_notify_resume(regs);

	if (cached_flags & _TIF_PATCH_PENDING)
	klp_update_patch_state(current);

	/* deal with pending signal delivery */
	if (cached_flags & _TIF_SIGPENDING)
	do_signal(regs);

	if (cached_flags & _TIF_NOTIFY_RESUME) {
	clear_thread_flag(TIF_NOTIFY_RESUME);
	tracehook_notify_resume(regs);
	rseq_handle_notify_resume(NULL, regs);
	}

	if (cached_flags & _TIF_USER_RETURN_NOTIFY)
	fire_user_return_notifiers();

	/* Disable IRQs and retry */
	local_irq_disable();

	cached_flags = READ_ONCE(current_thread_info()->flags);

	if (!(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
	break;
	}
	}

	static void __prepare_exit_to_usermode(struct pt_regs *regs)
	{
	struct thread_info *ti = current_thread_info();
	u32 cached_flags;

	addr_limit_user_check();

	lockdep_assert_irqs_disabled();
	lockdep_sys_exit();

	cached_flags = READ_ONCE(ti->flags);

	if (unlikely(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
	exit_to_usermode_loop(regs, cached_flags);

	/* Reload ti->flags; we may have rescheduled above. */
	cached_flags = READ_ONCE(ti->flags);

	if (unlikely(cached_flags & _TIF_IO_BITMAP))
	tss_update_io_bitmap();

	fpregs_assert_state_consistent();
	if (unlikely(cached_flags & _TIF_NEED_FPU_LOAD))
	switch_fpu_return();

	#ifdef CONFIG_COMPAT
	/*
	* Compat syscalls set TS_COMPAT. Make sure we clear it before
	* returning to user mode. We need to clear it after signal
	* handling, because syscall restart has a fixup for compat
	* syscalls. The fixup is exercised by the ptrace_syscall_32
	* selftest.
	*
	* We also need to clear TS_REGS_POKED_I386: the 32-bit tracer
	* special case only applies after poking regs and before the
	* very next return to user mode.
	*/
	ti->status &= ~(TS_COMPAT\|TS_I386_REGS_POKED);
	#endif
	}

	__visible noinstr void prepare_exit_to_usermode(struct pt_regs *regs)
	{
	instrumentation_begin();
	__prepare_exit_to_usermode(regs);
	instrumentation_end();
	exit_to_user_mode();
	}

	#define SYSCALL_EXIT_WORK_FLAGS \
	(_TIF_SYSCALL_TRACE \| _TIF_SYSCALL_AUDIT \| \
	_TIF_SINGLESTEP \| _TIF_SYSCALL_TRACEPOINT)

	static void syscall_slow_exit_work(struct pt_regs *regs, u32 cached_flags)
	{
	bool step;

	audit_syscall_exit(regs);

	if (cached_flags & _TIF_SYSCALL_TRACEPOINT)
	trace_sys_exit(regs, regs->ax);

	/*
	* If TIF_SYSCALL_EMU is set, we only get here because of
	* TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP).
	* We already reported this syscall instruction in
	* syscall_trace_enter().
	*/
	step = unlikely(
	(cached_flags & (_TIF_SINGLESTEP \| _TIF_SYSCALL_EMU))
	== _TIF_SINGLESTEP);
	if (step \|\| cached_flags & _TIF_SYSCALL_TRACE)
	tracehook_report_syscall_exit(regs, step);
	}

	static void __syscall_return_slowpath(struct pt_regs *regs)
	{
	struct thread_info *ti = current_thread_info();
	u32 cached_flags = READ_ONCE(ti->flags);

	CT_WARN_ON(ct_state() != CONTEXT_KERNEL);

	if (IS_ENABLED(CONFIG_PROVE_LOCKING) &&
	WARN(irqs_disabled(), "syscall %ld left IRQs disabled", regs->orig_ax))
	local_irq_enable();

	rseq_syscall(regs);

	/*
	* First do one-time work. If these work items are enabled, we
	* want to run them exactly once per syscall exit with IRQs on.
	*/
	if (unlikely(cached_flags & SYSCALL_EXIT_WORK_FLAGS))
	syscall_slow_exit_work(regs, cached_flags);

	local_irq_disable();
	__prepare_exit_to_usermode(regs);
	}

	/*
	* Called with IRQs on and fully valid regs. Returns with IRQs off in a
	* state such that we can immediately switch to user mode.
	*/
	__visible noinstr void syscall_return_slowpath(struct pt_regs *regs)
	{
	instrumentation_begin();
	__syscall_return_slowpath(regs);
	instrumentation_end();
	exit_to_user_mode();
	}

	#ifdef CONFIG_X86_64
	__visible noinstr void do_syscall_64(unsigned long nr, struct pt_regs *regs)
	{
	struct thread_info *ti;

	enter_from_user_mode();
	instrumentation_begin();

	local_irq_enable();
	ti = current_thread_info();
	if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY)
	nr = syscall_trace_enter(regs);

	if (likely(nr < NR_syscalls)) {
	nr = array_index_nospec(nr, NR_syscalls);
	regs->ax = sys_call_table[nr](regs);
	#ifdef CONFIG_X86_X32_ABI
	} else if (likely((nr & __X32_SYSCALL_BIT) &&
	(nr & ~__X32_SYSCALL_BIT) < X32_NR_syscalls)) {
	nr = array_index_nospec(nr & ~__X32_SYSCALL_BIT,
	X32_NR_syscalls);
	regs->ax = x32_sys_call_table[nr](regs);
	#endif
	}
	__syscall_return_slowpath(regs);

	instrumentation_end();
	exit_to_user_mode();
	}
	#endif

	#if defined(CONFIG_X86_32) \|\| defined(CONFIG_IA32_EMULATION)
	/*
	* Does a 32-bit syscall. Called with IRQs on in CONTEXT_KERNEL. Does
	* all entry and exit work and returns with IRQs off. This function is
	* extremely hot in workloads that use it, and it's usually called from
	* do_fast_syscall_32, so forcibly inline it to improve performance.
	*/
	static void do_syscall_32_irqs_on(struct pt_regs *regs)
	{
	struct thread_info *ti = current_thread_info();
	unsigned int nr = (unsigned int)regs->orig_ax;

	#ifdef CONFIG_IA32_EMULATION
	ti->status \|= TS_COMPAT;
	#endif

	if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY) {
	/*
	* Subtlety here: if ptrace pokes something larger than
	* 2^32-1 into orig_ax, this truncates it. This may or
	* may not be necessary, but it matches the old asm
	* behavior.
	*/
	nr = syscall_trace_enter(regs);
	}

	if (likely(nr < IA32_NR_syscalls)) {
	nr = array_index_nospec(nr, IA32_NR_syscalls);
	regs->ax = ia32_sys_call_table[nr](regs);
	}

	__syscall_return_slowpath(regs);
	}

	/* Handles int $0x80 */
	__visible noinstr void do_int80_syscall_32(struct pt_regs *regs)
	{
	enter_from_user_mode();
	instrumentation_begin();

	local_irq_enable();
	do_syscall_32_irqs_on(regs);

	instrumentation_end();
	exit_to_user_mode();
	}

	static bool __do_fast_syscall_32(struct pt_regs *regs)
	{
	int res;

	/* Fetch EBP from where the vDSO stashed it. */
	if (IS_ENABLED(CONFIG_X86_64)) {
	/*
	* Micro-optimization: the pointer we're following is
	* explicitly 32 bits, so it can't be out of range.
	*/
	res = __get_user((u32 )&regs->bp,
	(u32 __user __force *)(unsigned long)(u32)regs->sp);
	} else {
	res = get_user((u32 )&regs->bp,
	(u32 __user __force *)(unsigned long)(u32)regs->sp);
	}

	if (res) {
	/* User code screwed up. */
	regs->ax = -EFAULT;
	local_irq_disable();
	__prepare_exit_to_usermode(regs);
	return false;
	}

	/* Now this is just like a normal syscall. */
	do_syscall_32_irqs_on(regs);
	return true;
	}

	/* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */
	__visible noinstr long do_fast_syscall_32(struct pt_regs *regs)
	{
	/*
	* Called using the internal vDSO SYSENTER/SYSCALL32 calling
	* convention. Adjust regs so it looks like we entered using int80.
	*/
	unsigned long landing_pad = (unsigned long)current->mm->context.vdso +
	vdso_image_32.sym_int80_landing_pad;
	bool success;

	/*
	* SYSENTER loses EIP, and even SYSCALL32 needs us to skip forward
	* so that 'regs->ip -= 2' lands back on an int $0x80 instruction.
	* Fix it up.
	*/
	regs->ip = landing_pad;

	enter_from_user_mode();
	instrumentation_begin();

	local_irq_enable();
	success = __do_fast_syscall_32(regs);

	instrumentation_end();
	exit_to_user_mode();

	/* If it failed, keep it simple: use IRET. */
	if (!success)
	return 0;

	#ifdef CONFIG_X86_64
	/*
	* Opportunistic SYSRETL: if possible, try to return using SYSRETL.
	* SYSRETL is available on all 64-bit CPUs, so we don't need to
	* bother with SYSEXIT.
	*
	* Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
	* because the ECX fixup above will ensure that this is essentially
	* never the case.
	*/
	return regs->cs == __USER32_CS && regs->ss == __USER_DS &&
	regs->ip == landing_pad &&
	(regs->flags & (X86_EFLAGS_RF \| X86_EFLAGS_TF)) == 0;
	#else
	/*
	* Opportunistic SYSEXIT: if possible, try to return using SYSEXIT.
	*
	* Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
	* because the ECX fixup above will ensure that this is essentially
	* never the case.
	*
	* We don't allow syscalls at all from VM86 mode, but we still
	* need to check VM, because we might be returning from sys_vm86.
	*/
	return static_cpu_has(X86_FEATURE_SEP) &&
	regs->cs == __USER_CS && regs->ss == __USER_DS &&
	regs->ip == landing_pad &&
	(regs->flags & (X86_EFLAGS_RF \| X86_EFLAGS_TF \| X86_EFLAGS_VM)) == 0;
	#endif
	}
	#endif

	SYSCALL_DEFINE0(ni_syscall)
	{
	return -ENOSYS;
	}

	/**
	* idtentry_enter_cond_rcu - Handle state tracking on idtentry with conditional
	* RCU handling
	* @regs: Pointer to pt_regs of interrupted context
	*
	* Invokes:
	* - lockdep irqflag state tracking as low level ASM entry disabled
	* interrupts.
	*
	* - Context tracking if the exception hit user mode.
	*
	* - The hardirq tracer to keep the state consistent as low level ASM
	* entry disabled interrupts.
	*
	* For kernel mode entries RCU handling is done conditional. If RCU is
	* watching then the only RCU requirement is to check whether the tick has
	* to be restarted. If RCU is not watching then rcu_irq_enter() has to be
	* invoked on entry and rcu_irq_exit() on exit.
	*
	* Avoiding the rcu_irq_enter/exit() calls is an optimization but also
	* solves the problem of kernel mode pagefaults which can schedule, which
	* is not possible after invoking rcu_irq_enter() without undoing it.
	*
	* For user mode entries enter_from_user_mode() must be invoked to
	* establish the proper context for NOHZ_FULL. Otherwise scheduling on exit
	* would not be possible.
	*
	* Returns: True if RCU has been adjusted on a kernel entry
	* False otherwise
	*
	* The return value must be fed into the rcu_exit argument of
	* idtentry_exit_cond_rcu().
	*/
	bool noinstr idtentry_enter_cond_rcu(struct pt_regs *regs)
	{
	if (user_mode(regs)) {
	enter_from_user_mode();
	return false;
	}

	/*
	* If this entry hit the idle task invoke rcu_irq_enter() whether
	* RCU is watching or not.
	*
	* Interupts can nest when the first interrupt invokes softirq
	* processing on return which enables interrupts.
	*
	* Scheduler ticks in the idle task can mark quiescent state and
	* terminate a grace period, if and only if the timer interrupt is
	* not nested into another interrupt.
	*
	* Checking for __rcu_is_watching() here would prevent the nesting
	* interrupt to invoke rcu_irq_enter(). If that nested interrupt is
	* the tick then rcu_flavor_sched_clock_irq() would wrongfully
	* assume that it is the first interupt and eventually claim
	* quiescient state and end grace periods prematurely.
	*
	* Unconditionally invoke rcu_irq_enter() so RCU state stays
	* consistent.
	*
	* TINY_RCU does not support EQS, so let the compiler eliminate
	* this part when enabled.
	*/
	if (!IS_ENABLED(CONFIG_TINY_RCU) && is_idle_task(current)) {
	/*
	* If RCU is not watching then the same careful
	* sequence vs. lockdep and tracing is required
	* as in enter_from_user_mode().
	*/
	lockdep_hardirqs_off(CALLER_ADDR0);
	rcu_irq_enter();
	instrumentation_begin();
	trace_hardirqs_off_finish();
	instrumentation_end();

	return true;
	}

	/*
	* If RCU is watching then RCU only wants to check whether it needs
	* to restart the tick in NOHZ mode. rcu_irq_enter_check_tick()
	* already contains a warning when RCU is not watching, so no point
	* in having another one here.
	*/
	instrumentation_begin();
	rcu_irq_enter_check_tick();
	/* Use the combo lockdep/tracing function */
	trace_hardirqs_off();
	instrumentation_end();

	return false;
	}

	static void idtentry_exit_cond_resched(struct pt_regs *regs, bool may_sched)
	{
	if (may_sched && !preempt_count()) {
	/* Sanity check RCU and thread stack */
	rcu_irq_exit_check_preempt();
	if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
	WARN_ON_ONCE(!on_thread_stack());
	if (need_resched())
	preempt_schedule_irq();
	}
	/* Covers both tracing and lockdep */
	trace_hardirqs_on();
	}

	/**
	* idtentry_exit_cond_rcu - Handle return from exception with conditional RCU
	* handling
	* @regs: Pointer to pt_regs (exception entry regs)
	* @rcu_exit: Invoke rcu_irq_exit() if true
	*
	* Depending on the return target (kernel/user) this runs the necessary
	* preemption and work checks if possible and reguired and returns to
	* the caller with interrupts disabled and no further work pending.
	*
	* This is the last action before returning to the low level ASM code which
	* just needs to return to the appropriate context.
	*
	* Counterpart to idtentry_enter_cond_rcu(). The return value of the entry
	* function must be fed into the @rcu_exit argument.
	*/
	void noinstr idtentry_exit_cond_rcu(struct pt_regs *regs, bool rcu_exit)
	{
	lockdep_assert_irqs_disabled();

	/* Check whether this returns to user mode */
	if (user_mode(regs)) {
	prepare_exit_to_usermode(regs);
	} else if (regs->flags & X86_EFLAGS_IF) {
	/*
	* If RCU was not watching on entry this needs to be done
	* carefully and needs the same ordering of lockdep/tracing
	* and RCU as the return to user mode path.
	*/
	if (rcu_exit) {
	instrumentation_begin();
	/* Tell the tracer that IRET will enable interrupts */
	trace_hardirqs_on_prepare();
	lockdep_hardirqs_on_prepare(CALLER_ADDR0);
	instrumentation_end();
	rcu_irq_exit();
	lockdep_hardirqs_on(CALLER_ADDR0);
	return;
	}

	instrumentation_begin();
	idtentry_exit_cond_resched(regs, IS_ENABLED(CONFIG_PREEMPTION));
	instrumentation_end();
	} else {
	/*
	* IRQ flags state is correct already. Just tell RCU if it
	* was not watching on entry.
	*/
	if (rcu_exit)
	rcu_irq_exit();
	}
	}

	/**
	* idtentry_enter_user - Handle state tracking on idtentry from user mode
	* @regs: Pointer to pt_regs of interrupted context
	*
	* Invokes enter_from_user_mode() to establish the proper context for
	* NOHZ_FULL. Otherwise scheduling on exit would not be possible.
	*/
	void noinstr idtentry_enter_user(struct pt_regs *regs)
	{
	enter_from_user_mode();
	}

	/**
	* idtentry_exit_user - Handle return from exception to user mode
	* @regs: Pointer to pt_regs (exception entry regs)
	*
	* Runs the necessary preemption and work checks and returns to the caller
	* with interrupts disabled and no further work pending.
	*
	* This is the last action before returning to the low level ASM code which
	* just needs to return to the appropriate context.
	*
	* Counterpart to idtentry_enter_user().
	*/
	void noinstr idtentry_exit_user(struct pt_regs *regs)
	{
	lockdep_assert_irqs_disabled();

	prepare_exit_to_usermode(regs);
	}

	#ifdef CONFIG_XEN_PV
	#ifndef CONFIG_PREEMPTION
	/*
	* Some hypercalls issued by the toolstack can take many 10s of
	* seconds. Allow tasks running hypercalls via the privcmd driver to
	* be voluntarily preempted even if full kernel preemption is
	* disabled.
	*
	* Such preemptible hypercalls are bracketed by
	* xen_preemptible_hcall_begin() and xen_preemptible_hcall_end()
	* calls.
	*/
	DEFINE_PER_CPU(bool, xen_in_preemptible_hcall);
	EXPORT_SYMBOL_GPL(xen_in_preemptible_hcall);

	/*
	* In case of scheduling the flag must be cleared and restored after
	* returning from schedule as the task might move to a different CPU.
	*/
	static __always_inline bool get_and_clear_inhcall(void)
	{
	bool inhcall = __this_cpu_read(xen_in_preemptible_hcall);

	__this_cpu_write(xen_in_preemptible_hcall, false);
	return inhcall;
	}

	static __always_inline void restore_inhcall(bool inhcall)
	{
	__this_cpu_write(xen_in_preemptible_hcall, inhcall);
	}
	#else
	static __always_inline bool get_and_clear_inhcall(void) { return false; }
	static __always_inline void restore_inhcall(bool inhcall) { }
	#endif

	static void __xen_pv_evtchn_do_upcall(void)
	{
	irq_enter_rcu();
	inc_irq_stat(irq_hv_callback_count);

	xen_hvm_evtchn_do_upcall();

	irq_exit_rcu();
	}

	__visible noinstr void xen_pv_evtchn_do_upcall(struct pt_regs *regs)
	{
	struct pt_regs *old_regs;
	bool inhcall, rcu_exit;

	rcu_exit = idtentry_enter_cond_rcu(regs);
	old_regs = set_irq_regs(regs);

	instrumentation_begin();
	run_on_irqstack_cond(__xen_pv_evtchn_do_upcall, NULL, regs);
	instrumentation_begin();

	set_irq_regs(old_regs);

	inhcall = get_and_clear_inhcall();
	if (inhcall && !WARN_ON_ONCE(rcu_exit)) {
	instrumentation_begin();
	idtentry_exit_cond_resched(regs, true);
	instrumentation_end();
	restore_inhcall(inhcall);
	} else {
	idtentry_exit_cond_rcu(regs, rcu_exit);
	}
	}
	#endif /* CONFIG_XEN_PV */