Linux-libre 4.2-gnu

1 files changed, 1557 insertions, 0 deletions

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
new file mode 100644
index 000000000..8cb3e438f
--- /dev/null
+++ b/arch/x86/entry/entry_64.S
@@ -0,0 +1,1557 @@
+/*
+ *  linux/arch/x86_64/entry.S
+ *
+ *  Copyright (C) 1991, 1992  Linus Torvalds
+ *  Copyright (C) 2000, 2001, 2002  Andi Kleen SuSE Labs
+ *  Copyright (C) 2000  Pavel Machek <pavel@suse.cz>
+ *
+ * entry.S contains the system-call and fault low-level handling routines.
+ *
+ * Some of this is documented in Documentation/x86/entry_64.txt
+ *
+ * A note on terminology:
+ * - iret frame:	Architecture defined interrupt frame from SS to RIP
+ *			at the top of the kernel process stack.
+ *
+ * Some macro usage:
+ * - ENTRY/END:		Define functions in the symbol table.
+ * - TRACE_IRQ_*:	Trace hardirq state for lock debugging.
+ * - idtentry:		Define exception entry points.
+ */
+#include <linux/linkage.h>
+#include <asm/segment.h>
+#include <asm/cache.h>
+#include <asm/errno.h>
+#include "calling.h"
+#include <asm/asm-offsets.h>
+#include <asm/msr.h>
+#include <asm/unistd.h>
+#include <asm/thread_info.h>
+#include <asm/hw_irq.h>
+#include <asm/page_types.h>
+#include <asm/irqflags.h>
+#include <asm/paravirt.h>
+#include <asm/percpu.h>
+#include <asm/asm.h>
+#include <asm/context_tracking.h>
+#include <asm/smap.h>
+#include <asm/pgtable_types.h>
+#include <linux/err.h>
+
+/* Avoid __ASSEMBLER__'ifying <linux/audit.h> just for this.  */
+#include <linux/elf-em.h>
+#define AUDIT_ARCH_X86_64			(EM_X86_64|__AUDIT_ARCH_64BIT|__AUDIT_ARCH_LE)
+#define __AUDIT_ARCH_64BIT			0x80000000
+#define __AUDIT_ARCH_LE				0x40000000
+
+.code64
+.section .entry.text, "ax"
+
+#ifdef CONFIG_PARAVIRT
+ENTRY(native_usergs_sysret64)
+	swapgs
+	sysretq
+ENDPROC(native_usergs_sysret64)
+#endif /* CONFIG_PARAVIRT */
+
+.macro TRACE_IRQS_IRETQ
+#ifdef CONFIG_TRACE_IRQFLAGS
+	bt	$9, EFLAGS(%rsp)		/* interrupts off? */
+	jnc	1f
+	TRACE_IRQS_ON
+1:
+#endif
+.endm
+
+/*
+ * When dynamic function tracer is enabled it will add a breakpoint
+ * to all locations that it is about to modify, sync CPUs, update
+ * all the code, sync CPUs, then remove the breakpoints. In this time
+ * if lockdep is enabled, it might jump back into the debug handler
+ * outside the updating of the IST protection. (TRACE_IRQS_ON/OFF).
+ *
+ * We need to change the IDT table before calling TRACE_IRQS_ON/OFF to
+ * make sure the stack pointer does not get reset back to the top
+ * of the debug stack, and instead just reuses the current stack.
+ */
+#if defined(CONFIG_DYNAMIC_FTRACE) && defined(CONFIG_TRACE_IRQFLAGS)
+
+.macro TRACE_IRQS_OFF_DEBUG
+	call	debug_stack_set_zero
+	TRACE_IRQS_OFF
+	call	debug_stack_reset
+.endm
+
+.macro TRACE_IRQS_ON_DEBUG
+	call	debug_stack_set_zero
+	TRACE_IRQS_ON
+	call	debug_stack_reset
+.endm
+
+.macro TRACE_IRQS_IRETQ_DEBUG
+	bt	$9, EFLAGS(%rsp)		/* interrupts off? */
+	jnc	1f
+	TRACE_IRQS_ON_DEBUG
+1:
+.endm
+
+#else
+# define TRACE_IRQS_OFF_DEBUG			TRACE_IRQS_OFF
+# define TRACE_IRQS_ON_DEBUG			TRACE_IRQS_ON
+# define TRACE_IRQS_IRETQ_DEBUG			TRACE_IRQS_IRETQ
+#endif
+
+/*
+ * 64-bit SYSCALL instruction entry. Up to 6 arguments in registers.
+ *
+ * 64-bit SYSCALL saves rip to rcx, clears rflags.RF, then saves rflags to r11,
+ * then loads new ss, cs, and rip from previously programmed MSRs.
+ * rflags gets masked by a value from another MSR (so CLD and CLAC
+ * are not needed). SYSCALL does not save anything on the stack
+ * and does not change rsp.
+ *
+ * Registers on entry:
+ * rax  system call number
+ * rcx  return address
+ * r11  saved rflags (note: r11 is callee-clobbered register in C ABI)
+ * rdi  arg0
+ * rsi  arg1
+ * rdx  arg2
+ * r10  arg3 (needs to be moved to rcx to conform to C ABI)
+ * r8   arg4
+ * r9   arg5
+ * (note: r12-r15, rbp, rbx are callee-preserved in C ABI)
+ *
+ * Only called from user space.
+ *
+ * When user can change pt_regs->foo always force IRET. That is because
+ * it deals with uncanonical addresses better. SYSRET has trouble
+ * with them due to bugs in both AMD and Intel CPUs.
+ */
+
+ENTRY(entry_SYSCALL_64)
+	/*
+	 * Interrupts are off on entry.
+	 * We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON,
+	 * it is too small to ever cause noticeable irq latency.
+	 */
+	SWAPGS_UNSAFE_STACK
+	/*
+	 * A hypervisor implementation might want to use a label
+	 * after the swapgs, so that it can do the swapgs
+	 * for the guest and jump here on syscall.
+	 */
+GLOBAL(entry_SYSCALL_64_after_swapgs)
+
+	movq	%rsp, PER_CPU_VAR(rsp_scratch)
+	movq	PER_CPU_VAR(cpu_current_top_of_stack), %rsp
+
+	/* Construct struct pt_regs on stack */
+	pushq	$__USER_DS			/* pt_regs->ss */
+	pushq	PER_CPU_VAR(rsp_scratch)	/* pt_regs->sp */
+	/*
+	 * Re-enable interrupts.
+	 * We use 'rsp_scratch' as a scratch space, hence irq-off block above
+	 * must execute atomically in the face of possible interrupt-driven
+	 * task preemption. We must enable interrupts only after we're done
+	 * with using rsp_scratch:
+	 */
+	ENABLE_INTERRUPTS(CLBR_NONE)
+	pushq	%r11				/* pt_regs->flags */
+	pushq	$__USER_CS			/* pt_regs->cs */
+	pushq	%rcx				/* pt_regs->ip */
+	pushq	%rax				/* pt_regs->orig_ax */
+	pushq	%rdi				/* pt_regs->di */
+	pushq	%rsi				/* pt_regs->si */
+	pushq	%rdx				/* pt_regs->dx */
+	pushq	%rcx				/* pt_regs->cx */
+	pushq	$-ENOSYS			/* pt_regs->ax */
+	pushq	%r8				/* pt_regs->r8 */
+	pushq	%r9				/* pt_regs->r9 */
+	pushq	%r10				/* pt_regs->r10 */
+	pushq	%r11				/* pt_regs->r11 */
+	sub	$(6*8), %rsp			/* pt_regs->bp, bx, r12-15 not saved */
+
+	testl	$_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
+	jnz	tracesys
+entry_SYSCALL_64_fastpath:
+#if __SYSCALL_MASK == ~0
+	cmpq	$__NR_syscall_max, %rax
+#else
+	andl	$__SYSCALL_MASK, %eax
+	cmpl	$__NR_syscall_max, %eax
+#endif
+	ja	1f				/* return -ENOSYS (already in pt_regs->ax) */
+	movq	%r10, %rcx
+	call	*sys_call_table(, %rax, 8)
+	movq	%rax, RAX(%rsp)
+1:
+/*
+ * Syscall return path ending with SYSRET (fast path).
+ * Has incompletely filled pt_regs.
+ */
+	LOCKDEP_SYS_EXIT
+	/*
+	 * We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON,
+	 * it is too small to ever cause noticeable irq latency.
+	 */
+	DISABLE_INTERRUPTS(CLBR_NONE)
+
+	/*
+	 * We must check ti flags with interrupts (or at least preemption)
+	 * off because we must *never* return to userspace without
+	 * processing exit work that is enqueued if we're preempted here.
+	 * In particular, returning to userspace with any of the one-shot
+	 * flags (TIF_NOTIFY_RESUME, TIF_USER_RETURN_NOTIFY, etc) set is
+	 * very bad.
+	 */
+	testl	$_TIF_ALLWORK_MASK, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
+	jnz	int_ret_from_sys_call_irqs_off	/* Go to the slow path */
+
+	RESTORE_C_REGS_EXCEPT_RCX_R11
+	movq	RIP(%rsp), %rcx
+	movq	EFLAGS(%rsp), %r11
+	movq	RSP(%rsp), %rsp
+	/*
+	 * 64-bit SYSRET restores rip from rcx,
+	 * rflags from r11 (but RF and VM bits are forced to 0),
+	 * cs and ss are loaded from MSRs.
+	 * Restoration of rflags re-enables interrupts.
+	 *
+	 * NB: On AMD CPUs with the X86_BUG_SYSRET_SS_ATTRS bug, the ss
+	 * descriptor is not reinitialized.  This means that we should
+	 * avoid SYSRET with SS == NULL, which could happen if we schedule,
+	 * exit the kernel, and re-enter using an interrupt vector.  (All
+	 * interrupt entries on x86_64 set SS to NULL.)  We prevent that
+	 * from happening by reloading SS in __switch_to.  (Actually
+	 * detecting the failure in 64-bit userspace is tricky but can be
+	 * done.)
+	 */
+	USERGS_SYSRET64
+
+	/* Do syscall entry tracing */
+tracesys:
+	movq	%rsp, %rdi
+	movl	$AUDIT_ARCH_X86_64, %esi
+	call	syscall_trace_enter_phase1
+	test	%rax, %rax
+	jnz	tracesys_phase2			/* if needed, run the slow path */
+	RESTORE_C_REGS_EXCEPT_RAX		/* else restore clobbered regs */
+	movq	ORIG_RAX(%rsp), %rax
+	jmp	entry_SYSCALL_64_fastpath	/* and return to the fast path */
+
+tracesys_phase2:
+	SAVE_EXTRA_REGS
+	movq	%rsp, %rdi
+	movl	$AUDIT_ARCH_X86_64, %esi
+	movq	%rax, %rdx
+	call	syscall_trace_enter_phase2
+
+	/*
+	 * Reload registers from stack in case ptrace changed them.
+	 * We don't reload %rax because syscall_trace_entry_phase2() returned
+	 * the value it wants us to use in the table lookup.
+	 */
+	RESTORE_C_REGS_EXCEPT_RAX
+	RESTORE_EXTRA_REGS
+#if __SYSCALL_MASK == ~0
+	cmpq	$__NR_syscall_max, %rax
+#else
+	andl	$__SYSCALL_MASK, %eax
+	cmpl	$__NR_syscall_max, %eax
+#endif
+	ja	1f				/* return -ENOSYS (already in pt_regs->ax) */
+	movq	%r10, %rcx			/* fixup for C */
+	call	*sys_call_table(, %rax, 8)
+	movq	%rax, RAX(%rsp)
+1:
+	/* Use IRET because user could have changed pt_regs->foo */
+
+/*
+ * Syscall return path ending with IRET.
+ * Has correct iret frame.
+ */
+GLOBAL(int_ret_from_sys_call)
+	DISABLE_INTERRUPTS(CLBR_NONE)
+int_ret_from_sys_call_irqs_off: /* jumps come here from the irqs-off SYSRET path */
+	TRACE_IRQS_OFF
+	movl	$_TIF_ALLWORK_MASK, %edi
+	/* edi:	mask to check */
+GLOBAL(int_with_check)
+	LOCKDEP_SYS_EXIT_IRQ
+	GET_THREAD_INFO(%rcx)
+	movl	TI_flags(%rcx), %edx
+	andl	%edi, %edx
+	jnz	int_careful
+	andl	$~TS_COMPAT, TI_status(%rcx)
+	jmp	syscall_return
+
+	/*
+	 * Either reschedule or signal or syscall exit tracking needed.
+	 * First do a reschedule test.
+	 * edx:	work, edi: workmask
+	 */
+int_careful:
+	bt	$TIF_NEED_RESCHED, %edx
+	jnc	int_very_careful
+	TRACE_IRQS_ON
+	ENABLE_INTERRUPTS(CLBR_NONE)
+	pushq	%rdi
+	SCHEDULE_USER
+	popq	%rdi
+	DISABLE_INTERRUPTS(CLBR_NONE)
+	TRACE_IRQS_OFF
+	jmp	int_with_check
+
+	/* handle signals and tracing -- both require a full pt_regs */
+int_very_careful:
+	TRACE_IRQS_ON
+	ENABLE_INTERRUPTS(CLBR_NONE)
+	SAVE_EXTRA_REGS
+	/* Check for syscall exit trace */
+	testl	$_TIF_WORK_SYSCALL_EXIT, %edx
+	jz	int_signal
+	pushq	%rdi
+	leaq	8(%rsp), %rdi			/* &ptregs -> arg1 */
+	call	syscall_trace_leave
+	popq	%rdi
+	andl	$~(_TIF_WORK_SYSCALL_EXIT|_TIF_SYSCALL_EMU), %edi
+	jmp	int_restore_rest
+
+int_signal:
+	testl	$_TIF_DO_NOTIFY_MASK, %edx
+	jz	1f
+	movq	%rsp, %rdi			/* &ptregs -> arg1 */
+	xorl	%esi, %esi			/* oldset -> arg2 */
+	call	do_notify_resume
+1:	movl	$_TIF_WORK_MASK, %edi
+int_restore_rest:
+	RESTORE_EXTRA_REGS
+	DISABLE_INTERRUPTS(CLBR_NONE)
+	TRACE_IRQS_OFF
+	jmp	int_with_check
+
+syscall_return:
+	/* The IRETQ could re-enable interrupts: */
+	DISABLE_INTERRUPTS(CLBR_ANY)
+	TRACE_IRQS_IRETQ
+
+	/*
+	 * Try to use SYSRET instead of IRET if we're returning to
+	 * a completely clean 64-bit userspace context.
+	 */
+	movq	RCX(%rsp), %rcx
+	movq	RIP(%rsp), %r11
+	cmpq	%rcx, %r11			/* RCX == RIP */
+	jne	opportunistic_sysret_failed
+
+	/*
+	 * On Intel CPUs, SYSRET with non-canonical RCX/RIP will #GP
+	 * in kernel space.  This essentially lets the user take over
+	 * the kernel, since userspace controls RSP.
+	 *
+	 * If width of "canonical tail" ever becomes variable, this will need
+	 * to be updated to remain correct on both old and new CPUs.
+	 */
+	.ifne __VIRTUAL_MASK_SHIFT - 47
+	.error "virtual address width changed -- SYSRET checks need update"
+	.endif
+
+	/* Change top 16 bits to be the sign-extension of 47th bit */
+	shl	$(64 - (__VIRTUAL_MASK_SHIFT+1)), %rcx
+	sar	$(64 - (__VIRTUAL_MASK_SHIFT+1)), %rcx
+
+	/* If this changed %rcx, it was not canonical */
+	cmpq	%rcx, %r11
+	jne	opportunistic_sysret_failed
+
+	cmpq	$__USER_CS, CS(%rsp)		/* CS must match SYSRET */
+	jne	opportunistic_sysret_failed
+
+	movq	R11(%rsp), %r11
+	cmpq	%r11, EFLAGS(%rsp)		/* R11 == RFLAGS */
+	jne	opportunistic_sysret_failed
+
+	/*
+	 * SYSRET can't restore RF.  SYSRET can restore TF, but unlike IRET,
+	 * restoring TF results in a trap from userspace immediately after
+	 * SYSRET.  This would cause an infinite loop whenever #DB happens
+	 * with register state that satisfies the opportunistic SYSRET
+	 * conditions.  For example, single-stepping this user code:
+	 *
+	 *           movq	$stuck_here, %rcx
+	 *           pushfq
+	 *           popq %r11
+	 *   stuck_here:
+	 *
+	 * would never get past 'stuck_here'.
+	 */
+	testq	$(X86_EFLAGS_RF|X86_EFLAGS_TF), %r11
+	jnz	opportunistic_sysret_failed
+
+	/* nothing to check for RSP */
+
+	cmpq	$__USER_DS, SS(%rsp)		/* SS must match SYSRET */
+	jne	opportunistic_sysret_failed
+
+	/*
+	 * We win! This label is here just for ease of understanding
+	 * perf profiles. Nothing jumps here.
+	 */
+syscall_return_via_sysret:
+	/* rcx and r11 are already restored (see code above) */
+	RESTORE_C_REGS_EXCEPT_RCX_R11
+	movq	RSP(%rsp), %rsp
+	USERGS_SYSRET64
+
+opportunistic_sysret_failed:
+	SWAPGS
+	jmp	restore_c_regs_and_iret
+END(entry_SYSCALL_64)
+
+
+	.macro FORK_LIKE func
+ENTRY(stub_\func)
+	SAVE_EXTRA_REGS 8
+	jmp	sys_\func
+END(stub_\func)
+	.endm
+
+	FORK_LIKE  clone
+	FORK_LIKE  fork
+	FORK_LIKE  vfork
+
+ENTRY(stub_execve)
+	call	sys_execve
+return_from_execve:
+	testl	%eax, %eax
+	jz	1f
+	/* exec failed, can use fast SYSRET code path in this case */
+	ret
+1:
+	/* must use IRET code path (pt_regs->cs may have changed) */
+	addq	$8, %rsp
+	ZERO_EXTRA_REGS
+	movq	%rax, RAX(%rsp)
+	jmp	int_ret_from_sys_call
+END(stub_execve)
+/*
+ * Remaining execve stubs are only 7 bytes long.
+ * ENTRY() often aligns to 16 bytes, which in this case has no benefits.
+ */
+	.align	8
+GLOBAL(stub_execveat)
+	call	sys_execveat
+	jmp	return_from_execve
+END(stub_execveat)
+
+#if defined(CONFIG_X86_X32_ABI) || defined(CONFIG_IA32_EMULATION)
+	.align	8
+GLOBAL(stub_x32_execve)
+GLOBAL(stub32_execve)
+	call	compat_sys_execve
+	jmp	return_from_execve
+END(stub32_execve)
+END(stub_x32_execve)
+	.align	8
+GLOBAL(stub_x32_execveat)
+GLOBAL(stub32_execveat)
+	call	compat_sys_execveat
+	jmp	return_from_execve
+END(stub32_execveat)
+END(stub_x32_execveat)
+#endif
+
+/*
+ * sigreturn is special because it needs to restore all registers on return.
+ * This cannot be done with SYSRET, so use the IRET return path instead.
+ */
+ENTRY(stub_rt_sigreturn)
+	/*
+	 * SAVE_EXTRA_REGS result is not normally needed:
+	 * sigreturn overwrites all pt_regs->GPREGS.
+	 * But sigreturn can fail (!), and there is no easy way to detect that.
+	 * To make sure RESTORE_EXTRA_REGS doesn't restore garbage on error,
+	 * we SAVE_EXTRA_REGS here.
+	 */
+	SAVE_EXTRA_REGS 8
+	call	sys_rt_sigreturn
+return_from_stub:
+	addq	$8, %rsp
+	RESTORE_EXTRA_REGS
+	movq	%rax, RAX(%rsp)
+	jmp	int_ret_from_sys_call
+END(stub_rt_sigreturn)
+
+#ifdef CONFIG_X86_X32_ABI
+ENTRY(stub_x32_rt_sigreturn)
+	SAVE_EXTRA_REGS 8
+	call	sys32_x32_rt_sigreturn
+	jmp	return_from_stub
+END(stub_x32_rt_sigreturn)
+#endif
+
+/*
+ * A newly forked process directly context switches into this address.
+ *
+ * rdi: prev task we switched from
+ */
+ENTRY(ret_from_fork)
+
+	LOCK ; btr $TIF_FORK, TI_flags(%r8)
+
+	pushq	$0x0002
+	popfq					/* reset kernel eflags */
+
+	call	schedule_tail			/* rdi: 'prev' task parameter */
+
+	RESTORE_EXTRA_REGS
+
+	testb	$3, CS(%rsp)			/* from kernel_thread? */
+
+	/*
+	 * By the time we get here, we have no idea whether our pt_regs,
+	 * ti flags, and ti status came from the 64-bit SYSCALL fast path,
+	 * the slow path, or one of the 32-bit compat paths.
+	 * Use IRET code path to return, since it can safely handle
+	 * all of the above.
+	 */
+	jnz	int_ret_from_sys_call
+
+	/*
+	 * We came from kernel_thread
+	 * nb: we depend on RESTORE_EXTRA_REGS above
+	 */
+	movq	%rbp, %rdi
+	call	*%rbx
+	movl	$0, RAX(%rsp)
+	RESTORE_EXTRA_REGS
+	jmp	int_ret_from_sys_call
+END(ret_from_fork)
+
+/*
+ * Build the entry stubs with some assembler magic.
+ * We pack 1 stub into every 8-byte block.
+ */
+	.align 8
+ENTRY(irq_entries_start)
+    vector=FIRST_EXTERNAL_VECTOR
+    .rept (FIRST_SYSTEM_VECTOR - FIRST_EXTERNAL_VECTOR)
+	pushq	$(~vector+0x80)			/* Note: always in signed byte range */
+    vector=vector+1
+	jmp	common_interrupt
+	.align	8
+    .endr
+END(irq_entries_start)
+
+/*
+ * Interrupt entry/exit.
+ *
+ * Interrupt entry points save only callee clobbered registers in fast path.
+ *
+ * Entry runs with interrupts off.
+ */
+
+/* 0(%rsp): ~(interrupt number) */
+	.macro interrupt func
+	cld
+	/*
+	 * Since nothing in interrupt handling code touches r12...r15 members
+	 * of "struct pt_regs", and since interrupts can nest, we can save
+	 * four stack slots and simultaneously provide
+	 * an unwind-friendly stack layout by saving "truncated" pt_regs
+	 * exactly up to rbp slot, without these members.
+	 */
+	ALLOC_PT_GPREGS_ON_STACK -RBP
+	SAVE_C_REGS -RBP
+	/* this goes to 0(%rsp) for unwinder, not for saving the value: */
+	SAVE_EXTRA_REGS_RBP -RBP
+
+	leaq	-RBP(%rsp), %rdi		/* arg1 for \func (pointer to pt_regs) */
+
+	testb	$3, CS-RBP(%rsp)
+	jz	1f
+	SWAPGS
+1:
+	/*
+	 * Save previous stack pointer, optionally switch to interrupt stack.
+	 * irq_count is used to check if a CPU is already on an interrupt stack
+	 * or not. While this is essentially redundant with preempt_count it is
+	 * a little cheaper to use a separate counter in the PDA (short of
+	 * moving irq_enter into assembly, which would be too much work)
+	 */
+	movq	%rsp, %rsi
+	incl	PER_CPU_VAR(irq_count)
+	cmovzq	PER_CPU_VAR(irq_stack_ptr), %rsp
+	pushq	%rsi
+	/* We entered an interrupt context - irqs are off: */
+	TRACE_IRQS_OFF
+
+	call	\func
+	.endm
+
+	/*
+	 * The interrupt stubs push (~vector+0x80) onto the stack and
+	 * then jump to common_interrupt.
+	 */
+	.p2align CONFIG_X86_L1_CACHE_SHIFT
+common_interrupt:
+	ASM_CLAC
+	addq	$-0x80, (%rsp)			/* Adjust vector to [-256, -1] range */
+	interrupt do_IRQ
+	/* 0(%rsp): old RSP */
+ret_from_intr:
+	DISABLE_INTERRUPTS(CLBR_NONE)
+	TRACE_IRQS_OFF
+	decl	PER_CPU_VAR(irq_count)
+
+	/* Restore saved previous stack */
+	popq	%rsi
+	/* return code expects complete pt_regs - adjust rsp accordingly: */
+	leaq	-RBP(%rsi), %rsp
+
+	testb	$3, CS(%rsp)
+	jz	retint_kernel
+	/* Interrupt came from user space */
+retint_user:
+	GET_THREAD_INFO(%rcx)
+
+	/* %rcx: thread info. Interrupts are off. */
+retint_with_reschedule:
+	movl	$_TIF_WORK_MASK, %edi
+retint_check:
+	LOCKDEP_SYS_EXIT_IRQ
+	movl	TI_flags(%rcx), %edx
+	andl	%edi, %edx
+	jnz	retint_careful
+
+retint_swapgs:					/* return to user-space */
+	/*
+	 * The iretq could re-enable interrupts:
+	 */
+	DISABLE_INTERRUPTS(CLBR_ANY)
+	TRACE_IRQS_IRETQ
+
+	SWAPGS
+	jmp	restore_c_regs_and_iret
+
+/* Returning to kernel space */
+retint_kernel:
+#ifdef CONFIG_PREEMPT
+	/* Interrupts are off */
+	/* Check if we need preemption */
+	bt	$9, EFLAGS(%rsp)		/* were interrupts off? */
+	jnc	1f
+0:	cmpl	$0, PER_CPU_VAR(__preempt_count)
+	jnz	1f
+	call	preempt_schedule_irq
+	jmp	0b
+1:
+#endif
+	/*
+	 * The iretq could re-enable interrupts:
+	 */
+	TRACE_IRQS_IRETQ
+
+/*
+ * At this label, code paths which return to kernel and to user,
+ * which come from interrupts/exception and from syscalls, merge.
+ */
+restore_c_regs_and_iret:
+	RESTORE_C_REGS
+	REMOVE_PT_GPREGS_FROM_STACK 8
+	INTERRUPT_RETURN
+
+ENTRY(native_iret)
+	/*
+	 * Are we returning to a stack segment from the LDT?  Note: in
+	 * 64-bit mode SS:RSP on the exception stack is always valid.
+	 */
+#ifdef CONFIG_X86_ESPFIX64
+	testb	$4, (SS-RIP)(%rsp)
+	jnz	native_irq_return_ldt
+#endif
+
+.global native_irq_return_iret
+native_irq_return_iret:
+	/*
+	 * This may fault.  Non-paranoid faults on return to userspace are
+	 * handled by fixup_bad_iret.  These include #SS, #GP, and #NP.
+	 * Double-faults due to espfix64 are handled in do_double_fault.
+	 * Other faults here are fatal.
+	 */
+	iretq
+
+#ifdef CONFIG_X86_ESPFIX64
+native_irq_return_ldt:
+	pushq	%rax
+	pushq	%rdi
+	SWAPGS
+	movq	PER_CPU_VAR(espfix_waddr), %rdi
+	movq	%rax, (0*8)(%rdi)		/* RAX */
+	movq	(2*8)(%rsp), %rax		/* RIP */
+	movq	%rax, (1*8)(%rdi)
+	movq	(3*8)(%rsp), %rax		/* CS */
+	movq	%rax, (2*8)(%rdi)
+	movq	(4*8)(%rsp), %rax		/* RFLAGS */
+	movq	%rax, (3*8)(%rdi)
+	movq	(6*8)(%rsp), %rax		/* SS */
+	movq	%rax, (5*8)(%rdi)
+	movq	(5*8)(%rsp), %rax		/* RSP */
+	movq	%rax, (4*8)(%rdi)
+	andl	$0xffff0000, %eax
+	popq	%rdi
+	orq	PER_CPU_VAR(espfix_stack), %rax
+	SWAPGS
+	movq	%rax, %rsp
+	popq	%rax
+	jmp	native_irq_return_iret
+#endif
+
+	/* edi: workmask, edx: work */
+retint_careful:
+	bt	$TIF_NEED_RESCHED, %edx
+	jnc	retint_signal
+	TRACE_IRQS_ON
+	ENABLE_INTERRUPTS(CLBR_NONE)
+	pushq	%rdi
+	SCHEDULE_USER
+	popq	%rdi
+	GET_THREAD_INFO(%rcx)
+	DISABLE_INTERRUPTS(CLBR_NONE)
+	TRACE_IRQS_OFF
+	jmp	retint_check
+
+retint_signal:
+	testl	$_TIF_DO_NOTIFY_MASK, %edx
+	jz	retint_swapgs
+	TRACE_IRQS_ON
+	ENABLE_INTERRUPTS(CLBR_NONE)
+	SAVE_EXTRA_REGS
+	movq	$-1, ORIG_RAX(%rsp)
+	xorl	%esi, %esi			/* oldset */
+	movq	%rsp, %rdi			/* &pt_regs */
+	call	do_notify_resume
+	RESTORE_EXTRA_REGS
+	DISABLE_INTERRUPTS(CLBR_NONE)
+	TRACE_IRQS_OFF
+	GET_THREAD_INFO(%rcx)
+	jmp	retint_with_reschedule
+
+END(common_interrupt)
+
+/*
+ * APIC interrupts.
+ */
+.macro apicinterrupt3 num sym do_sym
+ENTRY(\sym)
+	ASM_CLAC
+	pushq	$~(\num)
+.Lcommon_\sym:
+	interrupt \do_sym
+	jmp	ret_from_intr
+END(\sym)
+.endm
+
+#ifdef CONFIG_TRACING
+#define trace(sym) trace_##sym
+#define smp_trace(sym) smp_trace_##sym
+
+.macro trace_apicinterrupt num sym
+apicinterrupt3 \num trace(\sym) smp_trace(\sym)
+.endm
+#else
+.macro trace_apicinterrupt num sym do_sym
+.endm
+#endif
+
+.macro apicinterrupt num sym do_sym
+apicinterrupt3 \num \sym \do_sym
+trace_apicinterrupt \num \sym
+.endm
+
+#ifdef CONFIG_SMP
+apicinterrupt3 IRQ_MOVE_CLEANUP_VECTOR		irq_move_cleanup_interrupt	smp_irq_move_cleanup_interrupt
+apicinterrupt3 REBOOT_VECTOR			reboot_interrupt		smp_reboot_interrupt
+#endif
+
+#ifdef CONFIG_X86_UV
+apicinterrupt3 UV_BAU_MESSAGE			uv_bau_message_intr1		uv_bau_message_interrupt
+#endif
+
+apicinterrupt LOCAL_TIMER_VECTOR		apic_timer_interrupt		smp_apic_timer_interrupt
+apicinterrupt X86_PLATFORM_IPI_VECTOR		x86_platform_ipi		smp_x86_platform_ipi
+
+#ifdef CONFIG_HAVE_KVM
+apicinterrupt3 POSTED_INTR_VECTOR		kvm_posted_intr_ipi		smp_kvm_posted_intr_ipi
+apicinterrupt3 POSTED_INTR_WAKEUP_VECTOR	kvm_posted_intr_wakeup_ipi	smp_kvm_posted_intr_wakeup_ipi
+#endif
+
+#ifdef CONFIG_X86_MCE_THRESHOLD
+apicinterrupt THRESHOLD_APIC_VECTOR		threshold_interrupt		smp_threshold_interrupt
+#endif
+
+#ifdef CONFIG_X86_MCE_AMD
+apicinterrupt DEFERRED_ERROR_VECTOR		deferred_error_interrupt	smp_deferred_error_interrupt
+#endif
+
+#ifdef CONFIG_X86_THERMAL_VECTOR
+apicinterrupt THERMAL_APIC_VECTOR		thermal_interrupt		smp_thermal_interrupt
+#endif
+
+#ifdef CONFIG_SMP
+apicinterrupt CALL_FUNCTION_SINGLE_VECTOR	call_function_single_interrupt	smp_call_function_single_interrupt
+apicinterrupt CALL_FUNCTION_VECTOR		call_function_interrupt		smp_call_function_interrupt
+apicinterrupt RESCHEDULE_VECTOR			reschedule_interrupt		smp_reschedule_interrupt
+#endif
+
+apicinterrupt ERROR_APIC_VECTOR			error_interrupt			smp_error_interrupt
+apicinterrupt SPURIOUS_APIC_VECTOR		spurious_interrupt		smp_spurious_interrupt
+
+#ifdef CONFIG_IRQ_WORK
+apicinterrupt IRQ_WORK_VECTOR			irq_work_interrupt		smp_irq_work_interrupt
+#endif
+
+/*
+ * Exception entry points.
+ */
+#define CPU_TSS_IST(x) PER_CPU_VAR(cpu_tss) + (TSS_ist + ((x) - 1) * 8)
+
+.macro idtentry sym do_sym has_error_code:req paranoid=0 shift_ist=-1
+ENTRY(\sym)
+	/* Sanity check */
+	.if \shift_ist != -1 && \paranoid == 0
+	.error "using shift_ist requires paranoid=1"
+	.endif
+
+	ASM_CLAC
+	PARAVIRT_ADJUST_EXCEPTION_FRAME
+
+	.ifeq \has_error_code
+	pushq	$-1				/* ORIG_RAX: no syscall to restart */
+	.endif
+
+	ALLOC_PT_GPREGS_ON_STACK
+
+	.if \paranoid
+	.if \paranoid == 1
+	testb	$3, CS(%rsp)			/* If coming from userspace, switch stacks */
+	jnz	1f
+	.endif
+	call	paranoid_entry
+	.else
+	call	error_entry
+	.endif
+	/* returned flag: ebx=0: need swapgs on exit, ebx=1: don't need it */
+
+	.if \paranoid
+	.if \shift_ist != -1
+	TRACE_IRQS_OFF_DEBUG			/* reload IDT in case of recursion */
+	.else
+	TRACE_IRQS_OFF
+	.endif
+	.endif
+
+	movq	%rsp, %rdi			/* pt_regs pointer */
+
+	.if \has_error_code
+	movq	ORIG_RAX(%rsp), %rsi		/* get error code */
+	movq	$-1, ORIG_RAX(%rsp)		/* no syscall to restart */
+	.else
+	xorl	%esi, %esi			/* no error code */
+	.endif
+
+	.if \shift_ist != -1
+	subq	$EXCEPTION_STKSZ, CPU_TSS_IST(\shift_ist)
+	.endif
+
+	call	\do_sym
+
+	.if \shift_ist != -1
+	addq	$EXCEPTION_STKSZ, CPU_TSS_IST(\shift_ist)
+	.endif
+
+	/* these procedures expect "no swapgs" flag in ebx */
+	.if \paranoid
+	jmp	paranoid_exit
+	.else
+	jmp	error_exit
+	.endif
+
+	.if \paranoid == 1
+	/*
+	 * Paranoid entry from userspace.  Switch stacks and treat it
+	 * as a normal entry.  This means that paranoid handlers
+	 * run in real process context if user_mode(regs).
+	 */
+1:
+	call	error_entry
+
+
+	movq	%rsp, %rdi			/* pt_regs pointer */
+	call	sync_regs
+	movq	%rax, %rsp			/* switch stack */
+
+	movq	%rsp, %rdi			/* pt_regs pointer */
+
+	.if \has_error_code
+	movq	ORIG_RAX(%rsp), %rsi		/* get error code */
+	movq	$-1, ORIG_RAX(%rsp)		/* no syscall to restart */
+	.else
+	xorl	%esi, %esi			/* no error code */
+	.endif
+
+	call	\do_sym
+
+	jmp	error_exit			/* %ebx: no swapgs flag */
+	.endif
+END(\sym)
+.endm
+
+#ifdef CONFIG_TRACING
+.macro trace_idtentry sym do_sym has_error_code:req
+idtentry trace(\sym) trace(\do_sym) has_error_code=\has_error_code
+idtentry \sym \do_sym has_error_code=\has_error_code
+.endm
+#else
+.macro trace_idtentry sym do_sym has_error_code:req
+idtentry \sym \do_sym has_error_code=\has_error_code
+.endm
+#endif
+
+idtentry divide_error			do_divide_error			has_error_code=0
+idtentry overflow			do_overflow			has_error_code=0
+idtentry bounds				do_bounds			has_error_code=0
+idtentry invalid_op			do_invalid_op			has_error_code=0
+idtentry device_not_available		do_device_not_available		has_error_code=0
+idtentry double_fault			do_double_fault			has_error_code=1 paranoid=2
+idtentry coprocessor_segment_overrun	do_coprocessor_segment_overrun	has_error_code=0
+idtentry invalid_TSS			do_invalid_TSS			has_error_code=1
+idtentry segment_not_present		do_segment_not_present		has_error_code=1
+idtentry spurious_interrupt_bug		do_spurious_interrupt_bug	has_error_code=0
+idtentry coprocessor_error		do_coprocessor_error		has_error_code=0
+idtentry alignment_check		do_alignment_check		has_error_code=1
+idtentry simd_coprocessor_error		do_simd_coprocessor_error	has_error_code=0
+
+
+	/*
+	 * Reload gs selector with exception handling
+	 * edi:  new selector
+	 */
+ENTRY(native_load_gs_index)
+	pushfq
+	DISABLE_INTERRUPTS(CLBR_ANY & ~CLBR_RDI)
+	SWAPGS
+gs_change:
+	movl	%edi, %gs
+2:	mfence					/* workaround */
+	SWAPGS
+	popfq
+	ret
+END(native_load_gs_index)
+
+	_ASM_EXTABLE(gs_change, bad_gs)
+	.section .fixup, "ax"
+	/* running with kernelgs */
+bad_gs:
+	SWAPGS					/* switch back to user gs */
+	xorl	%eax, %eax
+	movl	%eax, %gs
+	jmp	2b
+	.previous
+
+/* Call softirq on interrupt stack. Interrupts are off. */
+ENTRY(do_softirq_own_stack)
+	pushq	%rbp
+	mov	%rsp, %rbp
+	incl	PER_CPU_VAR(irq_count)
+	cmove	PER_CPU_VAR(irq_stack_ptr), %rsp
+	push	%rbp				/* frame pointer backlink */
+	call	__do_softirq
+	leaveq
+	decl	PER_CPU_VAR(irq_count)
+	ret
+END(do_softirq_own_stack)
+
+#ifdef CONFIG_XEN
+idtentry xen_hypervisor_callback xen_do_hypervisor_callback has_error_code=0
+
+/*
+ * A note on the "critical region" in our callback handler.
+ * We want to avoid stacking callback handlers due to events occurring
+ * during handling of the last event. To do this, we keep events disabled
+ * until we've done all processing. HOWEVER, we must enable events before
+ * popping the stack frame (can't be done atomically) and so it would still
+ * be possible to get enough handler activations to overflow the stack.
+ * Although unlikely, bugs of that kind are hard to track down, so we'd
+ * like to avoid the possibility.
+ * So, on entry to the handler we detect whether we interrupted an
+ * existing activation in its critical region -- if so, we pop the current
+ * activation and restart the handler using the previous one.
+ */
+ENTRY(xen_do_hypervisor_callback)		/* do_hypervisor_callback(struct *pt_regs) */
+
+/*
+ * Since we don't modify %rdi, evtchn_do_upall(struct *pt_regs) will
+ * see the correct pointer to the pt_regs
+ */
+	movq	%rdi, %rsp			/* we don't return, adjust the stack frame */
+11:	incl	PER_CPU_VAR(irq_count)
+	movq	%rsp, %rbp
+	cmovzq	PER_CPU_VAR(irq_stack_ptr), %rsp
+	pushq	%rbp				/* frame pointer backlink */
+	call	xen_evtchn_do_upcall
+	popq	%rsp
+	decl	PER_CPU_VAR(irq_count)
+#ifndef CONFIG_PREEMPT
+	call	xen_maybe_preempt_hcall
+#endif
+	jmp	error_exit
+END(xen_do_hypervisor_callback)
+
+/*
+ * Hypervisor uses this for application faults while it executes.
+ * We get here for two reasons:
+ *  1. Fault while reloading DS, ES, FS or GS
+ *  2. Fault while executing IRET
+ * Category 1 we do not need to fix up as Xen has already reloaded all segment
+ * registers that could be reloaded and zeroed the others.
+ * Category 2 we fix up by killing the current process. We cannot use the
+ * normal Linux return path in this case because if we use the IRET hypercall
+ * to pop the stack frame we end up in an infinite loop of failsafe callbacks.
+ * We distinguish between categories by comparing each saved segment register
+ * with its current contents: any discrepancy means we in category 1.
+ */
+ENTRY(xen_failsafe_callback)
+	movl	%ds, %ecx
+	cmpw	%cx, 0x10(%rsp)
+	jne	1f
+	movl	%es, %ecx
+	cmpw	%cx, 0x18(%rsp)
+	jne	1f
+	movl	%fs, %ecx
+	cmpw	%cx, 0x20(%rsp)
+	jne	1f
+	movl	%gs, %ecx
+	cmpw	%cx, 0x28(%rsp)
+	jne	1f
+	/* All segments match their saved values => Category 2 (Bad IRET). */
+	movq	(%rsp), %rcx
+	movq	8(%rsp), %r11
+	addq	$0x30, %rsp
+	pushq	$0				/* RIP */
+	pushq	%r11
+	pushq	%rcx
+	jmp	general_protection
+1:	/* Segment mismatch => Category 1 (Bad segment). Retry the IRET. */
+	movq	(%rsp), %rcx
+	movq	8(%rsp), %r11
+	addq	$0x30, %rsp
+	pushq	$-1 /* orig_ax = -1 => not a system call */
+	ALLOC_PT_GPREGS_ON_STACK
+	SAVE_C_REGS
+	SAVE_EXTRA_REGS
+	jmp	error_exit
+END(xen_failsafe_callback)
+
+apicinterrupt3 HYPERVISOR_CALLBACK_VECTOR \
+	xen_hvm_callback_vector xen_evtchn_do_upcall
+
+#endif /* CONFIG_XEN */
+
+#if IS_ENABLED(CONFIG_HYPERV)
+apicinterrupt3 HYPERVISOR_CALLBACK_VECTOR \
+	hyperv_callback_vector hyperv_vector_handler
+#endif /* CONFIG_HYPERV */
+
+idtentry debug			do_debug		has_error_code=0	paranoid=1 shift_ist=DEBUG_STACK
+idtentry int3			do_int3			has_error_code=0	paranoid=1 shift_ist=DEBUG_STACK
+idtentry stack_segment		do_stack_segment	has_error_code=1
+
+#ifdef CONFIG_XEN
+idtentry xen_debug		do_debug		has_error_code=0
+idtentry xen_int3		do_int3			has_error_code=0
+idtentry xen_stack_segment	do_stack_segment	has_error_code=1
+#endif
+
+idtentry general_protection	do_general_protection	has_error_code=1
+trace_idtentry page_fault	do_page_fault		has_error_code=1
+
+#ifdef CONFIG_KVM_GUEST
+idtentry async_page_fault	do_async_page_fault	has_error_code=1
+#endif
+
+#ifdef CONFIG_X86_MCE
+idtentry machine_check					has_error_code=0	paranoid=1 do_sym=*machine_check_vector(%rip)
+#endif
+
+/*
+ * Save all registers in pt_regs, and switch gs if needed.
+ * Use slow, but surefire "are we in kernel?" check.
+ * Return: ebx=0: need swapgs on exit, ebx=1: otherwise
+ */
+ENTRY(paranoid_entry)
+	cld
+	SAVE_C_REGS 8
+	SAVE_EXTRA_REGS 8
+	movl	$1, %ebx
+	movl	$MSR_GS_BASE, %ecx
+	rdmsr
+	testl	%edx, %edx
+	js	1f				/* negative -> in kernel */
+	SWAPGS
+	xorl	%ebx, %ebx
+1:	ret
+END(paranoid_entry)
+
+/*
+ * "Paranoid" exit path from exception stack.  This is invoked
+ * only on return from non-NMI IST interrupts that came
+ * from kernel space.
+ *
+ * We may be returning to very strange contexts (e.g. very early
+ * in syscall entry), so checking for preemption here would
+ * be complicated.  Fortunately, we there's no good reason
+ * to try to handle preemption here.
+ *
+ * On entry, ebx is "no swapgs" flag (1: don't need swapgs, 0: need it)
+ */
+ENTRY(paranoid_exit)
+	DISABLE_INTERRUPTS(CLBR_NONE)
+	TRACE_IRQS_OFF_DEBUG
+	testl	%ebx, %ebx			/* swapgs needed? */
+	jnz	paranoid_exit_no_swapgs
+	TRACE_IRQS_IRETQ
+	SWAPGS_UNSAFE_STACK
+	jmp	paranoid_exit_restore
+paranoid_exit_no_swapgs:
+	TRACE_IRQS_IRETQ_DEBUG
+paranoid_exit_restore:
+	RESTORE_EXTRA_REGS
+	RESTORE_C_REGS
+	REMOVE_PT_GPREGS_FROM_STACK 8
+	INTERRUPT_RETURN
+END(paranoid_exit)
+
+/*
+ * Save all registers in pt_regs, and switch gs if needed.
+ * Return: EBX=0: came from user mode; EBX=1: otherwise
+ */
+ENTRY(error_entry)
+	cld
+	SAVE_C_REGS 8
+	SAVE_EXTRA_REGS 8
+	xorl	%ebx, %ebx
+	testb	$3, CS+8(%rsp)
+	jz	error_kernelspace
+
+	/* We entered from user mode */
+	SWAPGS
+
+error_entry_done:
+	TRACE_IRQS_OFF
+	ret
+
+	/*
+	 * There are two places in the kernel that can potentially fault with
+	 * usergs. Handle them here.  B stepping K8s sometimes report a
+	 * truncated RIP for IRET exceptions returning to compat mode. Check
+	 * for these here too.
+	 */
+error_kernelspace:
+	incl	%ebx
+	leaq	native_irq_return_iret(%rip), %rcx
+	cmpq	%rcx, RIP+8(%rsp)
+	je	error_bad_iret
+	movl	%ecx, %eax			/* zero extend */
+	cmpq	%rax, RIP+8(%rsp)
+	je	bstep_iret
+	cmpq	$gs_change, RIP+8(%rsp)
+	jne	error_entry_done
+
+	/*
+	 * hack: gs_change can fail with user gsbase.  If this happens, fix up
+	 * gsbase and proceed.  We'll fix up the exception and land in
+	 * gs_change's error handler with kernel gsbase.
+	 */
+	SWAPGS
+	jmp	error_entry_done
+
+bstep_iret:
+	/* Fix truncated RIP */
+	movq	%rcx, RIP+8(%rsp)
+	/* fall through */
+
+error_bad_iret:
+	/*
+	 * We came from an IRET to user mode, so we have user gsbase.
+	 * Switch to kernel gsbase:
+	 */
+	SWAPGS
+
+	/*
+	 * Pretend that the exception came from user mode: set up pt_regs
+	 * as if we faulted immediately after IRET and clear EBX so that
+	 * error_exit knows that we will be returning to user mode.
+	 */
+	mov	%rsp, %rdi
+	call	fixup_bad_iret
+	mov	%rax, %rsp
+	decl	%ebx
+	jmp	error_entry_done
+END(error_entry)
+
+
+/*
+ * On entry, EBS is a "return to kernel mode" flag:
+ *   1: already in kernel mode, don't need SWAPGS
+ *   0: user gsbase is loaded, we need SWAPGS and standard preparation for return to usermode
+ */
+ENTRY(error_exit)
+	movl	%ebx, %eax
+	RESTORE_EXTRA_REGS
+	DISABLE_INTERRUPTS(CLBR_NONE)
+	TRACE_IRQS_OFF
+	testl	%eax, %eax
+	jnz	retint_kernel
+	jmp	retint_user
+END(error_exit)
+
+/* Runs on exception stack */
+ENTRY(nmi)
+	PARAVIRT_ADJUST_EXCEPTION_FRAME
+	/*
+	 * We allow breakpoints in NMIs. If a breakpoint occurs, then
+	 * the iretq it performs will take us out of NMI context.
+	 * This means that we can have nested NMIs where the next
+	 * NMI is using the top of the stack of the previous NMI. We
+	 * can't let it execute because the nested NMI will corrupt the
+	 * stack of the previous NMI. NMI handlers are not re-entrant
+	 * anyway.
+	 *
+	 * To handle this case we do the following:
+	 *  Check the a special location on the stack that contains
+	 *  a variable that is set when NMIs are executing.
+	 *  The interrupted task's stack is also checked to see if it
+	 *  is an NMI stack.
+	 *  If the variable is not set and the stack is not the NMI
+	 *  stack then:
+	 *    o Set the special variable on the stack
+	 *    o Copy the interrupt frame into an "outermost" location on the
+	 *      stack
+	 *    o Copy the interrupt frame into an "iret" location on the stack
+	 *    o Continue processing the NMI
+	 *  If the variable is set or the previous stack is the NMI stack:
+	 *    o Modify the "iret" location to jump to the repeat_nmi
+	 *    o return back to the first NMI
+	 *
+	 * Now on exit of the first NMI, we first clear the stack variable
+	 * The NMI stack will tell any nested NMIs at that point that it is
+	 * nested. Then we pop the stack normally with iret, and if there was
+	 * a nested NMI that updated the copy interrupt stack frame, a
+	 * jump will be made to the repeat_nmi code that will handle the second
+	 * NMI.
+	 *
+	 * However, espfix prevents us from directly returning to userspace
+	 * with a single IRET instruction.  Similarly, IRET to user mode
+	 * can fault.  We therefore handle NMIs from user space like
+	 * other IST entries.
+	 */
+
+	/* Use %rdx as our temp variable throughout */
+	pushq	%rdx
+
+	testb	$3, CS-RIP+8(%rsp)
+	jz	.Lnmi_from_kernel
+
+	/*
+	 * NMI from user mode.  We need to run on the thread stack, but we
+	 * can't go through the normal entry paths: NMIs are masked, and
+	 * we don't want to enable interrupts, because then we'll end
+	 * up in an awkward situation in which IRQs are on but NMIs
+	 * are off.
+	 */
+
+	SWAPGS
+	cld
+	movq	%rsp, %rdx
+	movq	PER_CPU_VAR(cpu_current_top_of_stack), %rsp
+	pushq	5*8(%rdx)	/* pt_regs->ss */
+	pushq	4*8(%rdx)	/* pt_regs->rsp */
+	pushq	3*8(%rdx)	/* pt_regs->flags */
+	pushq	2*8(%rdx)	/* pt_regs->cs */
+	pushq	1*8(%rdx)	/* pt_regs->rip */
+	pushq   $-1		/* pt_regs->orig_ax */
+	pushq   %rdi		/* pt_regs->di */
+	pushq   %rsi		/* pt_regs->si */
+	pushq   (%rdx)		/* pt_regs->dx */
+	pushq   %rcx		/* pt_regs->cx */
+	pushq   %rax		/* pt_regs->ax */
+	pushq   %r8		/* pt_regs->r8 */
+	pushq   %r9		/* pt_regs->r9 */
+	pushq   %r10		/* pt_regs->r10 */
+	pushq   %r11		/* pt_regs->r11 */
+	pushq	%rbx		/* pt_regs->rbx */
+	pushq	%rbp		/* pt_regs->rbp */
+	pushq	%r12		/* pt_regs->r12 */
+	pushq	%r13		/* pt_regs->r13 */
+	pushq	%r14		/* pt_regs->r14 */
+	pushq	%r15		/* pt_regs->r15 */
+
+	/*
+	 * At this point we no longer need to worry about stack damage
+	 * due to nesting -- we're on the normal thread stack and we're
+	 * done with the NMI stack.
+	 */
+
+	movq	%rsp, %rdi
+	movq	$-1, %rsi
+	call	do_nmi
+
+	/*
+	 * Return back to user mode.  We must *not* do the normal exit
+	 * work, because we don't want to enable interrupts.  Fortunately,
+	 * do_nmi doesn't modify pt_regs.
+	 */
+	SWAPGS
+	jmp	restore_c_regs_and_iret
+
+.Lnmi_from_kernel:
+	/*
+	 * Here's what our stack frame will look like:
+	 * +---------------------------------------------------------+
+	 * | original SS                                             |
+	 * | original Return RSP                                     |
+	 * | original RFLAGS                                         |
+	 * | original CS                                             |
+	 * | original RIP                                            |
+	 * +---------------------------------------------------------+
+	 * | temp storage for rdx                                    |
+	 * +---------------------------------------------------------+
+	 * | "NMI executing" variable                                |
+	 * +---------------------------------------------------------+
+	 * | iret SS          } Copied from "outermost" frame        |
+	 * | iret Return RSP  } on each loop iteration; overwritten  |
+	 * | iret RFLAGS      } by a nested NMI to force another     |
+	 * | iret CS          } iteration if needed.                 |
+	 * | iret RIP         }                                      |
+	 * +---------------------------------------------------------+
+	 * | outermost SS          } initialized in first_nmi;       |
+	 * | outermost Return RSP  } will not be changed before      |
+	 * | outermost RFLAGS      } NMI processing is done.         |
+	 * | outermost CS          } Copied to "iret" frame on each  |
+	 * | outermost RIP         } iteration.                      |
+	 * +---------------------------------------------------------+
+	 * | pt_regs                                                 |
+	 * +---------------------------------------------------------+
+	 *
+	 * The "original" frame is used by hardware.  Before re-enabling
+	 * NMIs, we need to be done with it, and we need to leave enough
+	 * space for the asm code here.
+	 *
+	 * We return by executing IRET while RSP points to the "iret" frame.
+	 * That will either return for real or it will loop back into NMI
+	 * processing.
+	 *
+	 * The "outermost" frame is copied to the "iret" frame on each
+	 * iteration of the loop, so each iteration starts with the "iret"
+	 * frame pointing to the final return target.
+	 */
+
+	/*
+	 * Determine whether we're a nested NMI.
+	 *
+	 * If we interrupted kernel code between repeat_nmi and
+	 * end_repeat_nmi, then we are a nested NMI.  We must not
+	 * modify the "iret" frame because it's being written by
+	 * the outer NMI.  That's okay; the outer NMI handler is
+	 * about to about to call do_nmi anyway, so we can just
+	 * resume the outer NMI.
+	 */
+
+	movq	$repeat_nmi, %rdx
+	cmpq	8(%rsp), %rdx
+	ja	1f
+	movq	$end_repeat_nmi, %rdx
+	cmpq	8(%rsp), %rdx
+	ja	nested_nmi_out
+1:
+
+	/*
+	 * Now check "NMI executing".  If it's set, then we're nested.
+	 * This will not detect if we interrupted an outer NMI just
+	 * before IRET.
+	 */
+	cmpl	$1, -8(%rsp)
+	je	nested_nmi
+
+	/*
+	 * Now test if the previous stack was an NMI stack.  This covers
+	 * the case where we interrupt an outer NMI after it clears
+	 * "NMI executing" but before IRET.  We need to be careful, though:
+	 * there is one case in which RSP could point to the NMI stack
+	 * despite there being no NMI active: naughty userspace controls
+	 * RSP at the very beginning of the SYSCALL targets.  We can
+	 * pull a fast one on naughty userspace, though: we program
+	 * SYSCALL to mask DF, so userspace cannot cause DF to be set
+	 * if it controls the kernel's RSP.  We set DF before we clear
+	 * "NMI executing".
+	 */
+	lea	6*8(%rsp), %rdx
+	/* Compare the NMI stack (rdx) with the stack we came from (4*8(%rsp)) */
+	cmpq	%rdx, 4*8(%rsp)
+	/* If the stack pointer is above the NMI stack, this is a normal NMI */
+	ja	first_nmi
+
+	subq	$EXCEPTION_STKSZ, %rdx
+	cmpq	%rdx, 4*8(%rsp)
+	/* If it is below the NMI stack, it is a normal NMI */
+	jb	first_nmi
+
+	/* Ah, it is within the NMI stack. */
+
+	testb	$(X86_EFLAGS_DF >> 8), (3*8 + 1)(%rsp)
+	jz	first_nmi	/* RSP was user controlled. */
+
+	/* This is a nested NMI. */
+
+nested_nmi:
+	/*
+	 * Modify the "iret" frame to point to repeat_nmi, forcing another
+	 * iteration of NMI handling.
+	 */
+	subq	$8, %rsp
+	leaq	-10*8(%rsp), %rdx
+	pushq	$__KERNEL_DS
+	pushq	%rdx
+	pushfq
+	pushq	$__KERNEL_CS
+	pushq	$repeat_nmi
+
+	/* Put stack back */
+	addq	$(6*8), %rsp
+
+nested_nmi_out:
+	popq	%rdx
+
+	/* We are returning to kernel mode, so this cannot result in a fault. */
+	INTERRUPT_RETURN
+
+first_nmi:
+	/* Restore rdx. */
+	movq	(%rsp), %rdx
+
+	/* Make room for "NMI executing". */
+	pushq	$0
+
+	/* Leave room for the "iret" frame */
+	subq	$(5*8), %rsp
+
+	/* Copy the "original" frame to the "outermost" frame */
+	.rept 5
+	pushq	11*8(%rsp)
+	.endr
+
+	/* Everything up to here is safe from nested NMIs */
+
+#ifdef CONFIG_DEBUG_ENTRY
+	/*
+	 * For ease of testing, unmask NMIs right away.  Disabled by
+	 * default because IRET is very expensive.
+	 */
+	pushq	$0		/* SS */
+	pushq	%rsp		/* RSP (minus 8 because of the previous push) */
+	addq	$8, (%rsp)	/* Fix up RSP */
+	pushfq			/* RFLAGS */
+	pushq	$__KERNEL_CS	/* CS */
+	pushq	$1f		/* RIP */
+	INTERRUPT_RETURN	/* continues at repeat_nmi below */
+1:
+#endif
+
+repeat_nmi:
+	/*
+	 * If there was a nested NMI, the first NMI's iret will return
+	 * here. But NMIs are still enabled and we can take another
+	 * nested NMI. The nested NMI checks the interrupted RIP to see
+	 * if it is between repeat_nmi and end_repeat_nmi, and if so
+	 * it will just return, as we are about to repeat an NMI anyway.
+	 * This makes it safe to copy to the stack frame that a nested
+	 * NMI will update.
+	 *
+	 * RSP is pointing to "outermost RIP".  gsbase is unknown, but, if
+	 * we're repeating an NMI, gsbase has the same value that it had on
+	 * the first iteration.  paranoid_entry will load the kernel
+	 * gsbase if needed before we call do_nmi.  "NMI executing"
+	 * is zero.
+	 */
+	movq	$1, 10*8(%rsp)		/* Set "NMI executing". */
+
+	/*
+	 * Copy the "outermost" frame to the "iret" frame.  NMIs that nest
+	 * here must not modify the "iret" frame while we're writing to
+	 * it or it will end up containing garbage.
+	 */
+	addq	$(10*8), %rsp
+	.rept 5
+	pushq	-6*8(%rsp)
+	.endr
+	subq	$(5*8), %rsp
+end_repeat_nmi:
+
+	/*
+	 * Everything below this point can be preempted by a nested NMI.
+	 * If this happens, then the inner NMI will change the "iret"
+	 * frame to point back to repeat_nmi.
+	 */
+	pushq	$-1				/* ORIG_RAX: no syscall to restart */
+	ALLOC_PT_GPREGS_ON_STACK
+
+	/*
+	 * Use paranoid_entry to handle SWAPGS, but no need to use paranoid_exit
+	 * as we should not be calling schedule in NMI context.
+	 * Even with normal interrupts enabled. An NMI should not be
+	 * setting NEED_RESCHED or anything that normal interrupts and
+	 * exceptions might do.
+	 */
+	call	paranoid_entry
+
+	/* paranoidentry do_nmi, 0; without TRACE_IRQS_OFF */
+	movq	%rsp, %rdi
+	movq	$-1, %rsi
+	call	do_nmi
+
+	testl	%ebx, %ebx			/* swapgs needed? */
+	jnz	nmi_restore
+nmi_swapgs:
+	SWAPGS_UNSAFE_STACK
+nmi_restore:
+	RESTORE_EXTRA_REGS
+	RESTORE_C_REGS
+
+	/* Point RSP at the "iret" frame. */
+	REMOVE_PT_GPREGS_FROM_STACK 6*8
+
+	/*
+	 * Clear "NMI executing".  Set DF first so that we can easily
+	 * distinguish the remaining code between here and IRET from
+	 * the SYSCALL entry and exit paths.  On a native kernel, we
+	 * could just inspect RIP, but, on paravirt kernels,
+	 * INTERRUPT_RETURN can translate into a jump into a
+	 * hypercall page.
+	 */
+	std
+	movq	$0, 5*8(%rsp)		/* clear "NMI executing" */
+
+	/*
+	 * INTERRUPT_RETURN reads the "iret" frame and exits the NMI
+	 * stack in a single instruction.  We are returning to kernel
+	 * mode, so this cannot result in a fault.
+	 */
+	INTERRUPT_RETURN
+END(nmi)
+
+ENTRY(ignore_sysret)
+	mov	$-ENOSYS, %eax
+	sysret
+END(ignore_sysret)