arch/x86/entry/common.c - kernel/common - 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/entry-common.h>
 #include <linux/mm.h>
 #include <linux/smp.h>
 #include <linux/errno.h>
 #include <linux/ptrace.h>
 #include <linux/export.h>
 #include <linux/nospec.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/apic.h>
 #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>

 #ifdef CONFIG_X86_64

 static __always_inline bool do_syscall_x64(struct pt_regs *regs, int nr)
 {
 	/*
 	 * Convert negative numbers to very high and thus out of range
 	 * numbers for comparisons.
 	 */
 	unsigned int unr = nr;

 	if (likely(unr < NR_syscalls)) {
 		unr = array_index_nospec(unr, NR_syscalls);
 		regs->ax = sys_call_table[unr](regs);
 		return true;
 	}
 	return false;
 }

 static __always_inline bool do_syscall_x32(struct pt_regs *regs, int nr)
 {
 	/*
 	 * Adjust the starting offset of the table, and convert numbers
 	 * < __X32_SYSCALL_BIT to very high and thus out of range
 	 * numbers for comparisons.
 	 */
 	unsigned int xnr = nr - __X32_SYSCALL_BIT;

 	if (IS_ENABLED(CONFIG_X86_X32_ABI) && likely(xnr < X32_NR_syscalls)) {
 		xnr = array_index_nospec(xnr, X32_NR_syscalls);
 		regs->ax = x32_sys_call_table[xnr](regs);
 		return true;
 	}
 	return false;
 }

 __visible noinstr void do_syscall_64(struct pt_regs *regs, int nr)
 {
 	add_random_kstack_offset();
 	nr = syscall_enter_from_user_mode(regs, nr);

 	instrumentation_begin();

 	if (!do_syscall_x64(regs, nr) && !do_syscall_x32(regs, nr) && nr != -1) {
 		/* Invalid system call, but still a system call. */
 		regs->ax = __x64_sys_ni_syscall(regs);
 	}

 	instrumentation_end();
 	syscall_exit_to_user_mode(regs);
 }
 #endif

 #if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
 static __always_inline int syscall_32_enter(struct pt_regs *regs)
 {
 	if (IS_ENABLED(CONFIG_IA32_EMULATION))
 		current_thread_info()->status |= TS_COMPAT;

 	return (int)regs->orig_ax;
 }

 #ifdef CONFIG_IA32_EMULATION
 bool __ia32_enabled __ro_after_init = true;
 #endif

 /*
  * Invoke a 32-bit syscall.  Called with IRQs on in CONTEXT_KERNEL.
  */
 static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs, int nr)
 {
 	/*
 	 * Convert negative numbers to very high and thus out of range
 	 * numbers for comparisons.
 	 */
 	unsigned int unr = nr;

 	if (likely(unr < IA32_NR_syscalls)) {
 		unr = array_index_nospec(unr, IA32_NR_syscalls);
 		regs->ax = ia32_sys_call_table[unr](regs);
 	} else if (nr != -1) {
 		regs->ax = __ia32_sys_ni_syscall(regs);
 	}
 }

 #ifdef CONFIG_IA32_EMULATION
 static __always_inline bool int80_is_external(void)
 {
 	const unsigned int offs = (0x80 / 32) * 0x10;
 	const u32 bit = BIT(0x80 % 32);

 	/* The local APIC on XENPV guests is fake */
 	if (cpu_feature_enabled(X86_FEATURE_XENPV))
 		return false;

 	/*
 	 * If vector 0x80 is set in the APIC ISR then this is an external
 	 * interrupt. Either from broken hardware or injected by a VMM.
 	 *
 	 * Note: In guest mode this is only valid for secure guests where
 	 * the secure module fully controls the vAPIC exposed to the guest.
 	 */
 	return apic_read(APIC_ISR + offs) & bit;
 }

 /**
  * int80_emulation - 32-bit legacy syscall entry
  *
  * This entry point can be used by 32-bit and 64-bit programs to perform
  * 32-bit system calls.  Instances of INT $0x80 can be found inline in
  * various programs and libraries.  It is also used by the vDSO's
  * __kernel_vsyscall fallback for hardware that doesn't support a faster
  * entry method.  Restarted 32-bit system calls also fall back to INT
  * $0x80 regardless of what instruction was originally used to do the
  * system call.
  *
  * This is considered a slow path.  It is not used by most libc
  * implementations on modern hardware except during process startup.
  *
  * The arguments for the INT $0x80 based syscall are on stack in the
  * pt_regs structure:
  *   eax:				system call number
  *   ebx, ecx, edx, esi, edi, ebp:	arg1 - arg 6
  */
 DEFINE_IDTENTRY_RAW(int80_emulation)
 {
 	int nr;

 	/* Kernel does not use INT $0x80! */
 	if (unlikely(!user_mode(regs))) {
 		irqentry_enter(regs);
 		instrumentation_begin();
 		panic("Unexpected external interrupt 0x80\n");
 	}

 	/*
 	 * Establish kernel context for instrumentation, including for
 	 * int80_is_external() below which calls into the APIC driver.
 	 * Identical for soft and external interrupts.
 	 */
 	enter_from_user_mode(regs);

 	instrumentation_begin();
 	add_random_kstack_offset();

 	/* Validate that this is a soft interrupt to the extent possible */
 	if (unlikely(int80_is_external()))
 		panic("Unexpected external interrupt 0x80\n");

 	/*
 	 * The low level idtentry code pushed -1 into regs::orig_ax
 	 * and regs::ax contains the syscall number.
 	 *
 	 * User tracing code (ptrace or signal handlers) might assume
 	 * that the regs::orig_ax contains a 32-bit number on invoking
 	 * a 32-bit syscall.
 	 *
 	 * Establish the syscall convention by saving the 32bit truncated
 	 * syscall number in regs::orig_ax and by invalidating regs::ax.
 	 */
 	regs->orig_ax = regs->ax & GENMASK(31, 0);
 	regs->ax = -ENOSYS;

 	nr = syscall_32_enter(regs);

 	local_irq_enable();
 	nr = syscall_enter_from_user_mode_work(regs, nr);
 	do_syscall_32_irqs_on(regs, nr);

 	instrumentation_end();
 	syscall_exit_to_user_mode(regs);
 }
 #else /* CONFIG_IA32_EMULATION */

 /* Handles int $0x80 on a 32bit kernel */
 __visible noinstr void do_int80_syscall_32(struct pt_regs *regs)
 {
 	int nr = syscall_32_enter(regs);

 	add_random_kstack_offset();
 	/*
 	 * Subtlety here: if ptrace pokes something larger than 2^31-1 into
 	 * orig_ax, the int return value truncates it. This matches
 	 * the semantics of syscall_get_nr().
 	 */
 	nr = syscall_enter_from_user_mode(regs, nr);
 	instrumentation_begin();

 	do_syscall_32_irqs_on(regs, nr);

 	instrumentation_end();
 	syscall_exit_to_user_mode(regs);
 }
 #endif /* !CONFIG_IA32_EMULATION */

 static noinstr bool __do_fast_syscall_32(struct pt_regs *regs)
 {
 	int nr = syscall_32_enter(regs);
 	int res;

 	add_random_kstack_offset();
 	/*
 	 * This cannot use syscall_enter_from_user_mode() as it has to
 	 * fetch EBP before invoking any of the syscall entry work
 	 * functions.
 	 */
 	syscall_enter_from_user_mode_prepare(regs);

 	instrumentation_begin();
 	/* 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();
 		instrumentation_end();
 		irqentry_exit_to_user_mode(regs);
 		return false;
 	}

 	nr = syscall_enter_from_user_mode_work(regs, nr);

 	/* Now this is just like a normal syscall. */
 	do_syscall_32_irqs_on(regs, nr);

 	instrumentation_end();
 	syscall_exit_to_user_mode(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;

 	/*
 	 * 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;

 	/* Invoke the syscall. If it failed, keep it simple: use IRET. */
 	if (!__do_fast_syscall_32(regs))
 		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
 }

 /* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */
 __visible noinstr long do_SYSENTER_32(struct pt_regs *regs)
 {
 	/* SYSENTER loses RSP, but the vDSO saved it in RBP. */
 	regs->sp = regs->bp;

 	/* SYSENTER clobbers EFLAGS.IF.  Assume it was set in usermode. */
 	regs->flags |= X86_EFLAGS_IF;

 	return do_fast_syscall_32(regs);
 }
 #endif

 SYSCALL_DEFINE0(ni_syscall)
 {
 	return -ENOSYS;
 }

 #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(struct pt_regs *regs)
 {
 	struct pt_regs *old_regs = set_irq_regs(regs);

 	inc_irq_stat(irq_hv_callback_count);

 	xen_evtchn_do_upcall();

 	set_irq_regs(old_regs);
 }

 __visible noinstr void xen_pv_evtchn_do_upcall(struct pt_regs *regs)
 {
 	irqentry_state_t state = irqentry_enter(regs);
 	bool inhcall;

 	instrumentation_begin();
 	run_sysvec_on_irqstack_cond(__xen_pv_evtchn_do_upcall, regs);

 	inhcall = get_and_clear_inhcall();
 	if (inhcall && !WARN_ON_ONCE(state.exit_rcu)) {
 		irqentry_exit_cond_resched();
 		instrumentation_end();
 		restore_inhcall(inhcall);
 	} else {
 		instrumentation_end();
 		irqentry_exit(regs, state);
 	}
 }
 #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/entry-common.h>
	#include <linux/mm.h>
	#include <linux/smp.h>
	#include <linux/errno.h>
	#include <linux/ptrace.h>
	#include <linux/export.h>
	#include <linux/nospec.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/apic.h>
	#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>

	#ifdef CONFIG_X86_64

	static __always_inline bool do_syscall_x64(struct pt_regs *regs, int nr)
	{
	/*
	* Convert negative numbers to very high and thus out of range
	* numbers for comparisons.
	*/
	unsigned int unr = nr;

	if (likely(unr < NR_syscalls)) {
	unr = array_index_nospec(unr, NR_syscalls);
	regs->ax = sys_call_table[unr](regs);
	return true;
	}
	return false;
	}

	static __always_inline bool do_syscall_x32(struct pt_regs *regs, int nr)
	{
	/*
	* Adjust the starting offset of the table, and convert numbers
	* < __X32_SYSCALL_BIT to very high and thus out of range
	* numbers for comparisons.
	*/
	unsigned int xnr = nr - __X32_SYSCALL_BIT;

	if (IS_ENABLED(CONFIG_X86_X32_ABI) && likely(xnr < X32_NR_syscalls)) {
	xnr = array_index_nospec(xnr, X32_NR_syscalls);
	regs->ax = x32_sys_call_table[xnr](regs);
	return true;
	}
	return false;
	}

	__visible noinstr void do_syscall_64(struct pt_regs *regs, int nr)
	{
	add_random_kstack_offset();
	nr = syscall_enter_from_user_mode(regs, nr);

	instrumentation_begin();

	if (!do_syscall_x64(regs, nr) && !do_syscall_x32(regs, nr) && nr != -1) {
	/* Invalid system call, but still a system call. */
	regs->ax = __x64_sys_ni_syscall(regs);
	}

	instrumentation_end();
	syscall_exit_to_user_mode(regs);
	}
	#endif

	#if defined(CONFIG_X86_32) \|\| defined(CONFIG_IA32_EMULATION)
	static __always_inline int syscall_32_enter(struct pt_regs *regs)
	{
	if (IS_ENABLED(CONFIG_IA32_EMULATION))
	current_thread_info()->status \|= TS_COMPAT;

	return (int)regs->orig_ax;
	}

	#ifdef CONFIG_IA32_EMULATION
	bool __ia32_enabled __ro_after_init = true;
	#endif

	/*
	* Invoke a 32-bit syscall. Called with IRQs on in CONTEXT_KERNEL.
	*/
	static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs, int nr)
	{
	/*
	* Convert negative numbers to very high and thus out of range
	* numbers for comparisons.
	*/
	unsigned int unr = nr;

	if (likely(unr < IA32_NR_syscalls)) {
	unr = array_index_nospec(unr, IA32_NR_syscalls);
	regs->ax = ia32_sys_call_table[unr](regs);
	} else if (nr != -1) {
	regs->ax = __ia32_sys_ni_syscall(regs);
	}
	}

	#ifdef CONFIG_IA32_EMULATION
	static __always_inline bool int80_is_external(void)
	{
	const unsigned int offs = (0x80 / 32) * 0x10;
	const u32 bit = BIT(0x80 % 32);

	/* The local APIC on XENPV guests is fake */
	if (cpu_feature_enabled(X86_FEATURE_XENPV))
	return false;

	/*
	* If vector 0x80 is set in the APIC ISR then this is an external
	* interrupt. Either from broken hardware or injected by a VMM.
	*
	* Note: In guest mode this is only valid for secure guests where
	* the secure module fully controls the vAPIC exposed to the guest.
	*/
	return apic_read(APIC_ISR + offs) & bit;
	}

	/**
	* int80_emulation - 32-bit legacy syscall entry
	*
	* This entry point can be used by 32-bit and 64-bit programs to perform
	* 32-bit system calls. Instances of INT $0x80 can be found inline in
	* various programs and libraries. It is also used by the vDSO's
	* __kernel_vsyscall fallback for hardware that doesn't support a faster
	* entry method. Restarted 32-bit system calls also fall back to INT
	* $0x80 regardless of what instruction was originally used to do the
	* system call.
	*
	* This is considered a slow path. It is not used by most libc
	* implementations on modern hardware except during process startup.
	*
	* The arguments for the INT $0x80 based syscall are on stack in the
	* pt_regs structure:
	* eax: system call number
	* ebx, ecx, edx, esi, edi, ebp: arg1 - arg 6
	*/
	DEFINE_IDTENTRY_RAW(int80_emulation)
	{
	int nr;

	/* Kernel does not use INT $0x80! */
	if (unlikely(!user_mode(regs))) {
	irqentry_enter(regs);
	instrumentation_begin();
	panic("Unexpected external interrupt 0x80\n");
	}

	/*
	* Establish kernel context for instrumentation, including for
	* int80_is_external() below which calls into the APIC driver.
	* Identical for soft and external interrupts.
	*/
	enter_from_user_mode(regs);

	instrumentation_begin();
	add_random_kstack_offset();

	/* Validate that this is a soft interrupt to the extent possible */
	if (unlikely(int80_is_external()))
	panic("Unexpected external interrupt 0x80\n");

	/*
	* The low level idtentry code pushed -1 into regs::orig_ax
	* and regs::ax contains the syscall number.
	*
	* User tracing code (ptrace or signal handlers) might assume
	* that the regs::orig_ax contains a 32-bit number on invoking
	* a 32-bit syscall.
	*
	* Establish the syscall convention by saving the 32bit truncated
	* syscall number in regs::orig_ax and by invalidating regs::ax.
	*/
	regs->orig_ax = regs->ax & GENMASK(31, 0);
	regs->ax = -ENOSYS;

	nr = syscall_32_enter(regs);

	local_irq_enable();
	nr = syscall_enter_from_user_mode_work(regs, nr);
	do_syscall_32_irqs_on(regs, nr);

	instrumentation_end();
	syscall_exit_to_user_mode(regs);
	}
	#else /* CONFIG_IA32_EMULATION */

	/* Handles int $0x80 on a 32bit kernel */
	__visible noinstr void do_int80_syscall_32(struct pt_regs *regs)
	{
	int nr = syscall_32_enter(regs);

	add_random_kstack_offset();
	/*
	* Subtlety here: if ptrace pokes something larger than 2^31-1 into
	* orig_ax, the int return value truncates it. This matches
	* the semantics of syscall_get_nr().
	*/
	nr = syscall_enter_from_user_mode(regs, nr);
	instrumentation_begin();

	do_syscall_32_irqs_on(regs, nr);

	instrumentation_end();
	syscall_exit_to_user_mode(regs);
	}
	#endif /* !CONFIG_IA32_EMULATION */

	static noinstr bool __do_fast_syscall_32(struct pt_regs *regs)
	{
	int nr = syscall_32_enter(regs);
	int res;

	add_random_kstack_offset();
	/*
	* This cannot use syscall_enter_from_user_mode() as it has to
	* fetch EBP before invoking any of the syscall entry work
	* functions.
	*/
	syscall_enter_from_user_mode_prepare(regs);

	instrumentation_begin();
	/* 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();
	instrumentation_end();
	irqentry_exit_to_user_mode(regs);
	return false;
	}

	nr = syscall_enter_from_user_mode_work(regs, nr);

	/* Now this is just like a normal syscall. */
	do_syscall_32_irqs_on(regs, nr);

	instrumentation_end();
	syscall_exit_to_user_mode(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;

	/*
	* 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;

	/* Invoke the syscall. If it failed, keep it simple: use IRET. */
	if (!__do_fast_syscall_32(regs))
	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
	}

	/* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */
	__visible noinstr long do_SYSENTER_32(struct pt_regs *regs)
	{
	/* SYSENTER loses RSP, but the vDSO saved it in RBP. */
	regs->sp = regs->bp;

	/* SYSENTER clobbers EFLAGS.IF. Assume it was set in usermode. */
	regs->flags \|= X86_EFLAGS_IF;

	return do_fast_syscall_32(regs);
	}
	#endif

	SYSCALL_DEFINE0(ni_syscall)
	{
	return -ENOSYS;
	}

	#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(struct pt_regs *regs)
	{
	struct pt_regs *old_regs = set_irq_regs(regs);

	inc_irq_stat(irq_hv_callback_count);

	xen_evtchn_do_upcall();

	set_irq_regs(old_regs);
	}

	__visible noinstr void xen_pv_evtchn_do_upcall(struct pt_regs *regs)
	{
	irqentry_state_t state = irqentry_enter(regs);
	bool inhcall;

	instrumentation_begin();
	run_sysvec_on_irqstack_cond(__xen_pv_evtchn_do_upcall, regs);

	inhcall = get_and_clear_inhcall();
	if (inhcall && !WARN_ON_ONCE(state.exit_rcu)) {
	irqentry_exit_cond_resched();
	instrumentation_end();
	restore_inhcall(inhcall);
	} else {
	instrumentation_end();
	irqentry_exit(regs, state);
	}
	}
	#endif /* CONFIG_XEN_PV */