[GIT PULL] x86/asm changes for v3.20

Ingo Molnar
2015-02-09T09:21:59Z

Linus,

Please pull the latest x86-asm-for-linus git tree from:

git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86-asm-for-linus

# HEAD: b57c0b5175ddbe9b477801f9994a5b330702c1ba Merge tag 'pr-20150201-x86-entry' of git://git.kernel.org/pub/scm/linux/kernel/git/luto/linux into x86/asm

[ NOTE: there's a (single) RCU commit this tree depends on
semantically (734d16801349), which is also present in the
RCU tree, which might throw off your diffstat. ]

The main changes in this cycle were the x86/entry and
sysret enhancements from Andy Lutomirski, see merge commits
772a9aca125 and b57c0b5175dd for details.

out-of-topic modifications in x86-asm-for-linus:
--------------------------------------------------
kernel/rcu/tree.c # 734d16801349: rcu: Make rcu_nmi_enter() ha

Thanks,

Ingo

------------------>
Andrey Skvortsov (1):
x86, vdso: teach 'make clean' remove vdso64 binaries

Andy Lutomirski (8):
x86, entry: Switch stacks on a paranoid entry from userspace
x86, traps: Track entry into and exit from IST context
x86: Clean up current_stack_pointer
x86, traps: Add ist_begin_non_atomic and ist_end_non_atomic
x86_64 entry: Fix RCX for ptraced syscalls
x86, traps: Fix ist_enter from userspace
x86_64, entry: Use sysret to return to userspace when possible
x86_64, entry: Remove the syscall exit audit and schedule optimizations

Denys Vlasenko (3):
x86: entry_64.S: delete unused code
x86: ia32entry.S: fix wrong symbolic constant usage: R11->ARGOFFSET
x86: entry_64.S: fold SAVE_ARGS_IRQ macro into its sole user

Paul E. McKenney (1):
rcu: Make rcu_nmi_enter() handle nesting

Tony Luck (1):
x86, mce: Get rid of TIF_MCE_NOTIFY and associated mce tricks

Documentation/x86/entry_64.txt | 18 +-
Documentation/x86/x86_64/kernel-stacks | 8 +-
arch/x86/ia32/ia32entry.S | 4 +-
arch/x86/include/asm/calling.h | 1 -
arch/x86/include/asm/mce.h | 1 -
arch/x86/include/asm/thread_info.h | 15 +-
arch/x86/include/asm/traps.h | 6 +
arch/x86/kernel/cpu/mcheck/mce.c | 114 ++++--------
arch/x86/kernel/cpu/mcheck/p5.c | 6 +
arch/x86/kernel/cpu/mcheck/winchip.c | 5 +
arch/x86/kernel/entry_64.S | 317 +++++++++++++++------------------
arch/x86/kernel/irq_32.c | 13 +-
arch/x86/kernel/signal.c | 6 -
arch/x86/kernel/traps.c | 119 ++++++++++---
arch/x86/vdso/Makefile | 2 +-
kernel/rcu/tree.c | 66 +++++--
16 files changed, 374 insertions(+), 327 deletions(-)

diff --git a/Documentation/x86/entry_64.txt b/Documentation/x86/entry_64.txt
index 4a1c5c2dc5a9..9132b86176a3 100644
--- a/Documentation/x86/entry_64.txt
+++ b/Documentation/x86/entry_64.txt
@@ -78,9 +78,6 @@ The expensive (paranoid) way is to read back the MSR_GS_BASE value
xorl %ebx,%ebx
1: ret

-and the whole paranoid non-paranoid macro complexity is about whether
-to suffer that RDMSR cost.
-
If we are at an interrupt or user-trap/gate-alike boundary then we can
use the faster check: the stack will be a reliable indicator of
whether SWAPGS was already done: if we see that we are a secondary
@@ -93,6 +90,15 @@ which might have triggered right after a normal entry wrote CS to the
stack but before we executed SWAPGS, then the only safe way to check
for GS is the slower method: the RDMSR.

-So we try only to mark those entry methods 'paranoid' that absolutely
-need the more expensive check for the GS base - and we generate all
-'normal' entry points with the regular (faster) entry macros.
+Therefore, super-atomic entries (except NMI, which is handled separately)
+must use idtentry with paranoid=1 to handle gsbase correctly. This
+triggers three main behavior changes:
+
+ - Interrupt entry will use the slower gsbase check.
+ - Interrupt entry from user mode will switch off the IST stack.
+ - Interrupt exit to kernel mode will not attempt to reschedule.
+
+We try to only use IST entries and the paranoid entry code for vectors
+that absolutely need the more expensive check for the GS base - and we
+generate all 'normal' entry points with the regular (faster) paranoid=0
+variant.
diff --git a/Documentation/x86/x86_64/kernel-stacks b/Documentation/x86/x86_64/kernel-stacks
index a01eec5d1d0b..e3c8a49d1a2f 100644
--- a/Documentation/x86/x86_64/kernel-stacks
+++ b/Documentation/x86/x86_64/kernel-stacks
@@ -40,9 +40,11 @@ An IST is selected by a non-zero value in the IST field of an
interrupt-gate descriptor. When an interrupt occurs and the hardware
loads such a descriptor, the hardware automatically sets the new stack
pointer based on the IST value, then invokes the interrupt handler. If
-software wants to allow nested IST interrupts then the handler must
-adjust the IST values on entry to and exit from the interrupt handler.
-(This is occasionally done, e.g. for debug exceptions.)
+the interrupt came from user mode, then the interrupt handler prologue
+will switch back to the per-thread stack. If software wants to allow
+nested IST interrupts then the handler must adjust the IST values on
+entry to and exit from the interrupt handler. (This is occasionally
+done, e.g. for debug exceptions.)

Events with different IST codes (i.e. with different stacks) can be
nested. For example, a debug interrupt can safely be interrupted by an
diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
index 82e8a1d44658..156ebcab4ada 100644
--- a/arch/x86/ia32/ia32entry.S
+++ b/arch/x86/ia32/ia32entry.S
@@ -179,8 +179,8 @@ ENTRY(ia32_sysenter_target)
sysexit_from_sys_call:
andl $~TS_COMPAT,TI_status+THREAD_INFO(%rsp,RIP-ARGOFFSET)
/* clear IF, that popfq doesn't enable interrupts early */
- andl $~0x200,EFLAGS-R11(%rsp)
- movl RIP-R11(%rsp),%edx /* User %eip */
+ andl $~0x200,EFLAGS-ARGOFFSET(%rsp)
+ movl RIP-ARGOFFSET(%rsp),%edx /* User %eip */
CFI_REGISTER rip,rdx
RESTORE_ARGS 0,24,0,0,0,0
xorq %r8,%r8
diff --git a/arch/x86/include/asm/calling.h b/arch/x86/include/asm/calling.h
index 76659b67fd11..1f1297b46f83 100644
--- a/arch/x86/include/asm/calling.h
+++ b/arch/x86/include/asm/calling.h
@@ -83,7 +83,6 @@ For 32-bit we have the following conventions - kernel is built with
#define SS 160

#define ARGOFFSET R11
-#define SWFRAME ORIG_RAX

.macro SAVE_ARGS addskip=0, save_rcx=1, save_r891011=1, rax_enosys=0
subq $9*8+\addskip, %rsp
diff --git a/arch/x86/include/asm/mce.h b/arch/x86/include/asm/mce.h
index 51b26e895933..9b3de99dc004 100644
--- a/arch/x86/include/asm/mce.h
+++ b/arch/x86/include/asm/mce.h
@@ -190,7 +190,6 @@ enum mcp_flags {
void machine_check_poll(enum mcp_flags flags, mce_banks_t *b);

int mce_notify_irq(void);
-void mce_notify_process(void);

DECLARE_PER_CPU(struct mce, injectm);

diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index 547e344a6dc6..e82e95abc92b 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -75,7 +75,6 @@ struct thread_info {
#define TIF_SYSCALL_EMU 6 /* syscall emulation active */
#define TIF_SYSCALL_AUDIT 7 /* syscall auditing active */
#define TIF_SECCOMP 8 /* secure computing */
-#define TIF_MCE_NOTIFY 10 /* notify userspace of an MCE */
#define TIF_USER_RETURN_NOTIFY 11 /* notify kernel of userspace return */
#define TIF_UPROBE 12 /* breakpointed or singlestepping */
#define TIF_NOTSC 16 /* TSC is not accessible in userland */
@@ -100,7 +99,6 @@ struct thread_info {
#define _TIF_SYSCALL_EMU (1 << TIF_SYSCALL_EMU)
#define _TIF_SYSCALL_AUDIT (1 << TIF_SYSCALL_AUDIT)
#define _TIF_SECCOMP (1 << TIF_SECCOMP)
-#define _TIF_MCE_NOTIFY (1 << TIF_MCE_NOTIFY)
#define _TIF_USER_RETURN_NOTIFY (1 << TIF_USER_RETURN_NOTIFY)
#define _TIF_UPROBE (1 << TIF_UPROBE)
#define _TIF_NOTSC (1 << TIF_NOTSC)
@@ -140,7 +138,7 @@ struct thread_info {

/* Only used for 64 bit */
#define _TIF_DO_NOTIFY_MASK \
- (_TIF_SIGPENDING | _TIF_MCE_NOTIFY | _TIF_NOTIFY_RESUME | \
+ (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | \
_TIF_USER_RETURN_NOTIFY | _TIF_UPROBE)

/* flags to check in __switch_to() */
@@ -170,6 +168,17 @@ static inline struct thread_info *current_thread_info(void)
return ti;
}

+static inline unsigned long current_stack_pointer(void)
+{
+ unsigned long sp;
+#ifdef CONFIG_X86_64
+ asm("mov %%rsp,%0" : "=g" (sp));
+#else
+ asm("mov %%esp,%0" : "=g" (sp));
+#endif
+ return sp;
+}
+
#else /* !__ASSEMBLY__ */

/* how to get the thread information struct from ASM */
diff --git a/arch/x86/include/asm/traps.h b/arch/x86/include/asm/traps.h
index 707adc6549d8..4e49d7dff78e 100644
--- a/arch/x86/include/asm/traps.h
+++ b/arch/x86/include/asm/traps.h
@@ -1,6 +1,7 @@
#ifndef _ASM_X86_TRAPS_H
#define _ASM_X86_TRAPS_H

+#include <linux/context_tracking_state.h>
#include <linux/kprobes.h>

#include <asm/debugreg.h>
@@ -110,6 +111,11 @@ asmlinkage void smp_thermal_interrupt(void);
asmlinkage void mce_threshold_interrupt(void);
#endif

+extern enum ctx_state ist_enter(struct pt_regs *regs);
+extern void ist_exit(struct pt_regs *regs, enum ctx_state prev_state);
+extern void ist_begin_non_atomic(struct pt_regs *regs);
+extern void ist_end_non_atomic(void);
+
/* Interrupts/Exceptions */
enum {
X86_TRAP_DE = 0, /* 0, Divide-by-zero */
diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index d2c611699cd9..d23179900755 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -43,6 +43,7 @@
#include <linux/export.h>

#include <asm/processor.h>
+#include <asm/traps.h>
#include <asm/mce.h>
#include <asm/msr.h>

@@ -1003,51 +1004,6 @@ static void mce_clear_state(unsigned long *toclear)
}

/*
- * Need to save faulting physical address associated with a process
- * in the machine check handler some place where we can grab it back
- * later in mce_notify_process()
- */
-#define MCE_INFO_MAX 16
-
-struct mce_info {
- atomic_t inuse;
- struct task_struct *t;
- __u64 paddr;
- int restartable;
-} mce_info[MCE_INFO_MAX];
-
-static void mce_save_info(__u64 addr, int c)
-{
- struct mce_info *mi;
-
- for (mi = mce_info; mi < &mce_info[MCE_INFO_MAX]; mi++) {
- if (atomic_cmpxchg(&mi->inuse, 0, 1) == 0) {
- mi->t = current;
- mi->paddr = addr;
- mi->restartable = c;
- return;
- }
- }
-
- mce_panic("Too many concurrent recoverable errors", NULL, NULL);
-}
-
-static struct mce_info *mce_find_info(void)
-{
- struct mce_info *mi;
-
- for (mi = mce_info; mi < &mce_info[MCE_INFO_MAX]; mi++)
- if (atomic_read(&mi->inuse) && mi->t == current)
- return mi;
- return NULL;
-}
-
-static void mce_clear_info(struct mce_info *mi)
-{
- atomic_set(&mi->inuse, 0);
-}
-
-/*
* The actual machine check handler. This only handles real
* exceptions when something got corrupted coming in through int 18.
*
@@ -1063,6 +1019,7 @@ void do_machine_check(struct pt_regs *regs, long error_code)
{
struct mca_config *cfg = &mca_cfg;
struct mce m, *final;
+ enum ctx_state prev_state;
int i;
int worst = 0;
int severity;
@@ -1084,6 +1041,10 @@ void do_machine_check(struct pt_regs *regs, long error_code)
DECLARE_BITMAP(toclear, MAX_NR_BANKS);
DECLARE_BITMAP(valid_banks, MAX_NR_BANKS);
char *msg = "Unknown";
+ u64 recover_paddr = ~0ull;
+ int flags = MF_ACTION_REQUIRED;
+
+ prev_state = ist_enter(regs);

this_cpu_inc(mce_exception_count);

@@ -1203,9 +1164,9 @@ void do_machine_check(struct pt_regs *regs, long error_code)
if (no_way_out)
mce_panic("Fatal machine check on current CPU", &m, msg);
if (worst == MCE_AR_SEVERITY) {
- /* schedule action before return to userland */
- mce_save_info(m.addr, m.mcgstatus & MCG_STATUS_RIPV);
- set_thread_flag(TIF_MCE_NOTIFY);
+ recover_paddr = m.addr;
+ if (!(m.mcgstatus & MCG_STATUS_RIPV))
+ flags |= MF_MUST_KILL;
} else if (kill_it) {
force_sig(SIGBUS, current);
}
@@ -1216,6 +1177,27 @@ void do_machine_check(struct pt_regs *regs, long error_code)
mce_wrmsrl(MSR_IA32_MCG_STATUS, 0);
out:
sync_core();
+
+ if (recover_paddr == ~0ull)
+ goto done;
+
+ pr_err("Uncorrected hardware memory error in user-access at %llx",
+ recover_paddr);
+ /*
+ * We must call memory_failure() here even if the current process is
+ * doomed. We still need to mark the page as poisoned and alert any
+ * other users of the page.
+ */
+ ist_begin_non_atomic(regs);
+ local_irq_enable();
+ if (memory_failure(recover_paddr >> PAGE_SHIFT, MCE_VECTOR, flags) < 0) {
+ pr_err("Memory error not recovered");
+ force_sig(SIGBUS, current);
+ }
+ local_irq_disable();
+ ist_end_non_atomic();
+done:
+ ist_exit(regs, prev_state);
}
EXPORT_SYMBOL_GPL(do_machine_check);

@@ -1233,42 +1215,6 @@ int memory_failure(unsigned long pfn, int vector, int flags)
#endif

/*
- * Called in process context that interrupted by MCE and marked with
- * TIF_MCE_NOTIFY, just before returning to erroneous userland.
- * This code is allowed to sleep.
- * Attempt possible recovery such as calling the high level VM handler to
- * process any corrupted pages, and kill/signal current process if required.
- * Action required errors are handled here.
- */
-void mce_notify_process(void)
-{
- unsigned long pfn;
- struct mce_info *mi = mce_find_info();
- int flags = MF_ACTION_REQUIRED;
-
- if (!mi)
- mce_panic("Lost physical address for unconsumed uncorrectable error", NULL, NULL);
- pfn = mi->paddr >> PAGE_SHIFT;
-
- clear_thread_flag(TIF_MCE_NOTIFY);
-
- pr_err("Uncorrected hardware memory error in user-access at %llx",
- mi->paddr);
- /*
- * We must call memory_failure() here even if the current process is
- * doomed. We still need to mark the page as poisoned and alert any
- * other users of the page.
- */
- if (!mi->restartable)
- flags |= MF_MUST_KILL;
- if (memory_failure(pfn, MCE_VECTOR, flags) < 0) {
- pr_err("Memory error not recovered");
- force_sig(SIGBUS, current);
- }
- mce_clear_info(mi);
-}
-
-/*
* Action optional processing happens here (picking up
* from the list of faulting pages that do_machine_check()
* placed into the "ring").
diff --git a/arch/x86/kernel/cpu/mcheck/p5.c b/arch/x86/kernel/cpu/mcheck/p5.c
index a3042989398c..ec2663a708e4 100644
--- a/arch/x86/kernel/cpu/mcheck/p5.c
+++ b/arch/x86/kernel/cpu/mcheck/p5.c
@@ -8,6 +8,7 @@
#include <linux/smp.h>

#include <asm/processor.h>
+#include <asm/traps.h>
#include <asm/mce.h>
#include <asm/msr.h>

@@ -17,8 +18,11 @@ int mce_p5_enabled __read_mostly;
/* Machine check handler for Pentium class Intel CPUs: */
static void pentium_machine_check(struct pt_regs *regs, long error_code)
{
+ enum ctx_state prev_state;
u32 loaddr, hi, lotype;

+ prev_state = ist_enter(regs);
+
rdmsr(MSR_IA32_P5_MC_ADDR, loaddr, hi);
rdmsr(MSR_IA32_P5_MC_TYPE, lotype, hi);

@@ -33,6 +37,8 @@ static void pentium_machine_check(struct pt_regs *regs, long error_code)
}

add_taint(TAINT_MACHINE_CHECK, LOCKDEP_NOW_UNRELIABLE);
+
+ ist_exit(regs, prev_state);
}

/* Set up machine check reporting for processors with Intel style MCE: */
diff --git a/arch/x86/kernel/cpu/mcheck/winchip.c b/arch/x86/kernel/cpu/mcheck/winchip.c
index 7dc5564d0cdf..bd5d46a32210 100644
--- a/arch/x86/kernel/cpu/mcheck/winchip.c
+++ b/arch/x86/kernel/cpu/mcheck/winchip.c
@@ -7,14 +7,19 @@
#include <linux/types.h>

#include <asm/processor.h>
+#include <asm/traps.h>
#include <asm/mce.h>
#include <asm/msr.h>

/* Machine check handler for WinChip C6: */
static void winchip_machine_check(struct pt_regs *regs, long error_code)
{
+ enum ctx_state prev_state = ist_enter(regs);
+
printk(KERN_EMERG "CPU0: Machine Check Exception.\n");
add_taint(TAINT_MACHINE_CHECK, LOCKDEP_NOW_UNRELIABLE);
+
+ ist_exit(regs, prev_state);
}

/* Set up machine check reporting on the Winchip C6 series */
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 9ebaf63ba182..db13655c3a2a 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -143,7 +143,8 @@ ENDPROC(native_usergs_sysret64)
movq \tmp,RSP+\offset(%rsp)
movq $__USER_DS,SS+\offset(%rsp)
movq $__USER_CS,CS+\offset(%rsp)
- movq $-1,RCX+\offset(%rsp)
+ movq RIP+\offset(%rsp),\tmp /* get rip */
+ movq \tmp,RCX+\offset(%rsp) /* copy it to rcx as sysret would do */
movq R11+\offset(%rsp),\tmp /* get eflags */
movq \tmp,EFLAGS+\offset(%rsp)
.endm
@@ -155,27 +156,6 @@ ENDPROC(native_usergs_sysret64)
movq \tmp,R11+\offset(%rsp)
.endm

- .macro FAKE_STACK_FRAME child_rip
- /* push in order ss, rsp, eflags, cs, rip */
- xorl %eax, %eax
- pushq_cfi $__KERNEL_DS /* ss */
- /*CFI_REL_OFFSET ss,0*/
- pushq_cfi %rax /* rsp */
- CFI_REL_OFFSET rsp,0
- pushq_cfi $(X86_EFLAGS_IF|X86_EFLAGS_FIXED) /* eflags - interrupts on */
- /*CFI_REL_OFFSET rflags,0*/
- pushq_cfi $__KERNEL_CS /* cs */
- /*CFI_REL_OFFSET cs,0*/
- pushq_cfi \child_rip /* rip */
- CFI_REL_OFFSET rip,0
- pushq_cfi %rax /* orig rax */
- .endm
-
- .macro UNFAKE_STACK_FRAME
- addq $8*6, %rsp
- CFI_ADJUST_CFA_OFFSET -(6*8)
- .endm
-
/*
* initial frame state for interrupts (and exceptions without error code)
*/
@@ -238,51 +218,6 @@ ENDPROC(native_usergs_sysret64)
CFI_REL_OFFSET r15, R15+\offset
.endm

-/* save partial stack frame */
- .macro SAVE_ARGS_IRQ
- cld
- /* start from rbp in pt_regs and jump over */
- movq_cfi rdi, (RDI-RBP)
- movq_cfi rsi, (RSI-RBP)
- movq_cfi rdx, (RDX-RBP)
- movq_cfi rcx, (RCX-RBP)
- movq_cfi rax, (RAX-RBP)
- movq_cfi r8, (R8-RBP)
- movq_cfi r9, (R9-RBP)
- movq_cfi r10, (R10-RBP)
- movq_cfi r11, (R11-RBP)
-
- /* Save rbp so that we can unwind from get_irq_regs() */
- movq_cfi rbp, 0
-
- /* Save previous stack value */
- movq %rsp, %rsi
-
- leaq -RBP(%rsp),%rdi /* arg1 for handler */
- testl $3, CS-RBP(%rsi)
- je 1f
- SWAPGS
- /*
- * 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)
- */
-1: incl PER_CPU_VAR(irq_count)
- cmovzq PER_CPU_VAR(irq_stack_ptr),%rsp
- CFI_DEF_CFA_REGISTER rsi
-
- /* Store previous stack value */
- pushq %rsi
- CFI_ESCAPE 0x0f /* DW_CFA_def_cfa_expression */, 6, \
- 0x77 /* DW_OP_breg7 */, 0, \
- 0x06 /* DW_OP_deref */, \
- 0x08 /* DW_OP_const1u */, SS+8-RBP, \
- 0x22 /* DW_OP_plus */
- /* We entered an interrupt context - irqs are off: */
- TRACE_IRQS_OFF
- .endm
-
ENTRY(save_paranoid)
XCPT_FRAME 1 RDI+8
cld
@@ -426,15 +361,12 @@ GLOBAL(system_call_after_swapgs)
* Has incomplete stack frame and undefined top of stack.
*/
ret_from_sys_call:
- movl $_TIF_ALLWORK_MASK,%edi
- /* edi: flagmask */
-sysret_check:
+ testl $_TIF_ALLWORK_MASK,TI_flags+THREAD_INFO(%rsp,RIP-ARGOFFSET)
+ jnz int_ret_from_sys_call_fixup /* Go the the slow path */
+
LOCKDEP_SYS_EXIT
DISABLE_INTERRUPTS(CLBR_NONE)
TRACE_IRQS_OFF
- movl TI_flags+THREAD_INFO(%rsp,RIP-ARGOFFSET),%edx
- andl %edi,%edx
- jnz sysret_careful
CFI_REMEMBER_STATE
/*
* sysretq will re-enable interrupts:
@@ -448,49 +380,10 @@ GLOBAL(system_call_after_swapgs)
USERGS_SYSRET64

CFI_RESTORE_STATE
- /* Handle reschedules */
- /* edx: work, edi: workmask */
-sysret_careful:
- bt $TIF_NEED_RESCHED,%edx
- jnc sysret_signal
- TRACE_IRQS_ON
- ENABLE_INTERRUPTS(CLBR_NONE)
- pushq_cfi %rdi
- SCHEDULE_USER
- popq_cfi %rdi
- jmp sysret_check

- /* Handle a signal */
-sysret_signal:
- TRACE_IRQS_ON
- ENABLE_INTERRUPTS(CLBR_NONE)
-#ifdef CONFIG_AUDITSYSCALL
- bt $TIF_SYSCALL_AUDIT,%edx
- jc sysret_audit
-#endif
- /*
- * We have a signal, or exit tracing or single-step.
- * These all wind up with the iret return path anyway,
- * so just join that path right now.
- */
+int_ret_from_sys_call_fixup:
FIXUP_TOP_OF_STACK %r11, -ARGOFFSET
- jmp int_check_syscall_exit_work
-
-#ifdef CONFIG_AUDITSYSCALL
- /*
- * Return fast path for syscall audit. Call __audit_syscall_exit()
- * directly and then jump back to the fast path with TIF_SYSCALL_AUDIT
- * masked off.
- */
-sysret_audit:
- movq RAX-ARGOFFSET(%rsp),%rsi /* second arg, syscall return value */
- cmpq $-MAX_ERRNO,%rsi /* is it < -MAX_ERRNO? */
- setbe %al /* 1 if so, 0 if not */
- movzbl %al,%edi /* zero-extend that into %edi */
- call __audit_syscall_exit
- movl $(_TIF_ALLWORK_MASK & ~_TIF_SYSCALL_AUDIT),%edi
- jmp sysret_check
-#endif /* CONFIG_AUDITSYSCALL */
+ jmp int_ret_from_sys_call

/* Do syscall tracing */
tracesys:
@@ -626,19 +519,6 @@ END(\label)
FORK_LIKE vfork
FIXED_FRAME stub_iopl, sys_iopl

-ENTRY(ptregscall_common)
- DEFAULT_FRAME 1 8 /* offset 8: return address */
- RESTORE_TOP_OF_STACK %r11, 8
- movq_cfi_restore R15+8, r15
- movq_cfi_restore R14+8, r14
- movq_cfi_restore R13+8, r13
- movq_cfi_restore R12+8, r12
- movq_cfi_restore RBP+8, rbp
- movq_cfi_restore RBX+8, rbx
- ret $REST_SKIP /* pop extended registers */
- CFI_ENDPROC
-END(ptregscall_common)
-
ENTRY(stub_execve)
CFI_STARTPROC
addq $8, %rsp
@@ -779,7 +659,48 @@ END(interrupt)
/* reserve pt_regs for scratch regs and rbp */
subq $ORIG_RAX-RBP, %rsp
CFI_ADJUST_CFA_OFFSET ORIG_RAX-RBP
- SAVE_ARGS_IRQ
+ cld
+ /* start from rbp in pt_regs and jump over */
+ movq_cfi rdi, (RDI-RBP)
+ movq_cfi rsi, (RSI-RBP)
+ movq_cfi rdx, (RDX-RBP)
+ movq_cfi rcx, (RCX-RBP)
+ movq_cfi rax, (RAX-RBP)
+ movq_cfi r8, (R8-RBP)
+ movq_cfi r9, (R9-RBP)
+ movq_cfi r10, (R10-RBP)
+ movq_cfi r11, (R11-RBP)
+
+ /* Save rbp so that we can unwind from get_irq_regs() */
+ movq_cfi rbp, 0
+
+ /* Save previous stack value */
+ movq %rsp, %rsi
+
+ leaq -RBP(%rsp),%rdi /* arg1 for handler */
+ testl $3, CS-RBP(%rsi)
+ je 1f
+ SWAPGS
+ /*
+ * 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)
+ */
+1: incl PER_CPU_VAR(irq_count)
+ cmovzq PER_CPU_VAR(irq_stack_ptr),%rsp
+ CFI_DEF_CFA_REGISTER rsi
+
+ /* Store previous stack value */
+ pushq %rsi
+ CFI_ESCAPE 0x0f /* DW_CFA_def_cfa_expression */, 6, \
+ 0x77 /* DW_OP_breg7 */, 0, \
+ 0x06 /* DW_OP_deref */, \
+ 0x08 /* DW_OP_const1u */, SS+8-RBP, \
+ 0x22 /* DW_OP_plus */
+ /* We entered an interrupt context - irqs are off: */
+ TRACE_IRQS_OFF
+
call \func
.endm

@@ -831,6 +752,60 @@ retint_swapgs: /* return to user-space */
*/
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-R11)(%rsp), %rcx
+ cmpq %rcx,(RIP-R11)(%rsp) /* 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. It's not worth
+ * testing for canonicalness exactly -- this check detects any
+ * of the 17 high bits set, which is true for non-canonical
+ * or kernel addresses. (This will pessimize vsyscall=native.
+ * Big deal.)
+ *
+ * If virtual addresses ever become wider, 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
+ shr $__VIRTUAL_MASK_SHIFT, %rcx
+ jnz opportunistic_sysret_failed
+
+ cmpq $__USER_CS,(CS-R11)(%rsp) /* CS must match SYSRET */
+ jne opportunistic_sysret_failed
+
+ movq (R11-ARGOFFSET)(%rsp), %r11
+ cmpq %r11,(EFLAGS-ARGOFFSET)(%rsp) /* R11 == RFLAGS */
+ jne opportunistic_sysret_failed
+
+ testq $X86_EFLAGS_RF,%r11 /* sysret can't restore RF */
+ jnz opportunistic_sysret_failed
+
+ /* nothing to check for RSP */
+
+ cmpq $__USER_DS,(SS-ARGOFFSET)(%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.
+ */
+irq_return_via_sysret:
+ CFI_REMEMBER_STATE
+ RESTORE_ARGS 1,8,1
+ movq (RSP-RIP)(%rsp),%rsp
+ USERGS_SYSRET64
+ CFI_RESTORE_STATE
+
+opportunistic_sysret_failed:
SWAPGS
jmp restore_args

@@ -1048,6 +1023,11 @@ ENTRY(\sym)
CFI_ADJUST_CFA_OFFSET ORIG_RAX-R15

.if \paranoid
+ .if \paranoid == 1
+ CFI_REMEMBER_STATE
+ testl $3, CS(%rsp) /* If coming from userspace, switch */
+ jnz 1f /* stacks. */
+ .endif
call save_paranoid
.else
call error_entry
@@ -1088,6 +1068,36 @@ ENTRY(\sym)
jmp error_exit /* %ebx: no swapgs flag */
.endif

+ .if \paranoid == 1
+ CFI_RESTORE_STATE
+ /*
+ * 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
+
+ DEFAULT_FRAME 0
+
+ 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
+
CFI_ENDPROC
END(\sym)
.endm
@@ -1108,7 +1118,7 @@ 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=1
+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
@@ -1289,16 +1299,14 @@ idtentry machine_check has_error_code=0 paranoid=1 do_sym=*machine_check_vector(
#endif

/*
- * "Paranoid" exit path from exception stack.
- * Paranoid because this is used by NMIs and cannot take
- * any kernel state for granted.
- * We don't do kernel preemption checks here, because only
- * NMI should be common and it does not enable IRQs and
- * cannot get reschedule ticks.
+ * "Paranoid" exit path from exception stack. This is invoked
+ * only on return from non-NMI IST interrupts that came
+ * from kernel space.
*
- * "trace" is 0 for the NMI handler only, because irq-tracing
- * is fundamentally NMI-unsafe. (we cannot change the soft and
- * hard flags at once, atomically)
+ * 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.
*/

/* ebx: no swapgs flag */
@@ -1308,43 +1316,14 @@ ENTRY(paranoid_exit)
TRACE_IRQS_OFF_DEBUG
testl %ebx,%ebx /* swapgs needed? */
jnz paranoid_restore
- testl $3,CS(%rsp)
- jnz paranoid_userspace
-paranoid_swapgs:
TRACE_IRQS_IRETQ 0
SWAPGS_UNSAFE_STACK
RESTORE_ALL 8
- jmp irq_return
+ INTERRUPT_RETURN
paranoid_restore:
TRACE_IRQS_IRETQ_DEBUG 0
RESTORE_ALL 8
- jmp irq_return
-paranoid_userspace:
- GET_THREAD_INFO(%rcx)
- movl TI_flags(%rcx),%ebx
- andl $_TIF_WORK_MASK,%ebx
- jz paranoid_swapgs
- movq %rsp,%rdi /* &pt_regs */
- call sync_regs
- movq %rax,%rsp /* switch stack for scheduling */
- testl $_TIF_NEED_RESCHED,%ebx
- jnz paranoid_schedule
- movl %ebx,%edx /* arg3: thread flags */
- TRACE_IRQS_ON
- ENABLE_INTERRUPTS(CLBR_NONE)
- xorl %esi,%esi /* arg2: oldset */
- movq %rsp,%rdi /* arg1: &pt_regs */
- call do_notify_resume
- DISABLE_INTERRUPTS(CLBR_NONE)
- TRACE_IRQS_OFF
- jmp paranoid_userspace
-paranoid_schedule:
- TRACE_IRQS_ON
- ENABLE_INTERRUPTS(CLBR_ANY)
- SCHEDULE_USER
- DISABLE_INTERRUPTS(CLBR_ANY)
- TRACE_IRQS_OFF
- jmp paranoid_userspace
+ INTERRUPT_RETURN
CFI_ENDPROC
END(paranoid_exit)

diff --git a/arch/x86/kernel/irq_32.c b/arch/x86/kernel/irq_32.c
index 63ce838e5a54..28d28f5eb8f4 100644
--- a/arch/x86/kernel/irq_32.c
+++ b/arch/x86/kernel/irq_32.c
@@ -69,16 +69,9 @@ static void call_on_stack(void *func, void *stack)
: "memory", "cc", "edx", "ecx", "eax");
}

-/* how to get the current stack pointer from C */
-#define current_stack_pointer ({ \
- unsigned long sp; \
- asm("mov %%esp,%0" : "=g" (sp)); \
- sp; \
-})
-
static inline void *current_stack(void)
{
- return (void *)(current_stack_pointer & ~(THREAD_SIZE - 1));
+ return (void *)(current_stack_pointer() & ~(THREAD_SIZE - 1));
}

static inline int
@@ -103,7 +96,7 @@ execute_on_irq_stack(int overflow, struct irq_desc *desc, int irq)

/* Save the next esp at the bottom of the stack */
prev_esp = (u32 *)irqstk;
- *prev_esp = current_stack_pointer;
+ *prev_esp = current_stack_pointer();

if (unlikely(overflow))
call_on_stack(print_stack_overflow, isp);
@@ -156,7 +149,7 @@ void do_softirq_own_stack(void)

/* Push the previous esp onto the stack */
prev_esp = (u32 *)irqstk;
- *prev_esp = current_stack_pointer;
+ *prev_esp = current_stack_pointer();

call_on_stack(__do_softirq, isp);
}
diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index ed37a768d0fc..2a33c8f68319 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -740,12 +740,6 @@ do_notify_resume(struct pt_regs *regs, void *unused, __u32 thread_info_flags)
{
user_exit();

-#ifdef CONFIG_X86_MCE
- /* notify userspace of pending MCEs */
- if (thread_info_flags & _TIF_MCE_NOTIFY)
- mce_notify_process();
-#endif /* CONFIG_X86_64 && CONFIG_X86_MCE */
-
if (thread_info_flags & _TIF_UPROBE)
uprobe_notify_resume(regs);

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 88900e288021..c74f2f5652da 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -108,6 +108,88 @@ static inline void preempt_conditional_cli(struct pt_regs *regs)
preempt_count_dec();
}

+enum ctx_state ist_enter(struct pt_regs *regs)
+{
+ enum ctx_state prev_state;
+
+ if (user_mode_vm(regs)) {
+ /* Other than that, we're just an exception. */
+ prev_state = exception_enter();
+ } else {
+ /*
+ * We might have interrupted pretty much anything. In
+ * fact, if we're a machine check, we can even interrupt
+ * NMI processing. We don't want in_nmi() to return true,
+ * but we need to notify RCU.
+ */
+ rcu_nmi_enter();
+ prev_state = IN_KERNEL; /* the value is irrelevant. */
+ }
+
+ /*
+ * We are atomic because we're on the IST stack (or we're on x86_32,
+ * in which case we still shouldn't schedule).
+ *
+ * This must be after exception_enter(), because exception_enter()
+ * won't do anything if in_interrupt() returns true.
+ */
+ preempt_count_add(HARDIRQ_OFFSET);
+
+ /* This code is a bit fragile. Test it. */
+ rcu_lockdep_assert(rcu_is_watching(), "ist_enter didn't work");
+
+ return prev_state;
+}
+
+void ist_exit(struct pt_regs *regs, enum ctx_state prev_state)
+{
+ /* Must be before exception_exit. */
+ preempt_count_sub(HARDIRQ_OFFSET);
+
+ if (user_mode_vm(regs))
+ return exception_exit(prev_state);
+ else
+ rcu_nmi_exit();
+}
+
+/**
+ * ist_begin_non_atomic() - begin a non-atomic section in an IST exception
+ * @regs: regs passed to the IST exception handler
+ *
+ * IST exception handlers normally cannot schedule. As a special
+ * exception, if the exception interrupted userspace code (i.e.
+ * user_mode_vm(regs) would return true) and the exception was not
+ * a double fault, it can be safe to schedule. ist_begin_non_atomic()
+ * begins a non-atomic section within an ist_enter()/ist_exit() region.
+ * Callers are responsible for enabling interrupts themselves inside
+ * the non-atomic section, and callers must call is_end_non_atomic()
+ * before ist_exit().
+ */
+void ist_begin_non_atomic(struct pt_regs *regs)
+{
+ BUG_ON(!user_mode_vm(regs));
+
+ /*
+ * Sanity check: we need to be on the normal thread stack. This
+ * will catch asm bugs and any attempt to use ist_preempt_enable
+ * from double_fault.
+ */
+ BUG_ON(((current_stack_pointer() ^ this_cpu_read_stable(kernel_stack))
+ & ~(THREAD_SIZE - 1)) != 0);
+
+ preempt_count_sub(HARDIRQ_OFFSET);
+}
+
+/**
+ * ist_end_non_atomic() - begin a non-atomic section in an IST exception
+ *
+ * Ends a non-atomic section started with ist_begin_non_atomic().
+ */
+void ist_end_non_atomic(void)
+{
+ preempt_count_add(HARDIRQ_OFFSET);
+}
+
static nokprobe_inline int
do_trap_no_signal(struct task_struct *tsk, int trapnr, char *str,
struct pt_regs *regs, long error_code)
@@ -251,6 +333,8 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code)
* end up promoting it to a doublefault. In that case, modify
* the stack to make it look like we just entered the #GP
* handler from user space, similar to bad_iret.
+ *
+ * No need for ist_enter here because we don't use RCU.
*/
if (((long)regs->sp >> PGDIR_SHIFT) == ESPFIX_PGD_ENTRY &&
regs->cs == __KERNEL_CS &&
@@ -263,12 +347,12 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code)
normal_regs->orig_ax = 0; /* Missing (lost) #GP error code */
regs->ip = (unsigned long)general_protection;
regs->sp = (unsigned long)&normal_regs->orig_ax;
+
return;
}
#endif

- exception_enter();
- /* Return not checked because double check cannot be ignored */
+ ist_enter(regs); /* Discard prev_state because we won't return. */
notify_die(DIE_TRAP, str, regs, error_code, X86_TRAP_DF, SIGSEGV);

tsk->thread.error_code = error_code;
@@ -434,7 +518,7 @@ dotraplinkage void notrace do_int3(struct pt_regs *regs, long error_code)
if (poke_int3_handler(regs))
return;

- prev_state = exception_enter();
+ prev_state = ist_enter(regs);
#ifdef CONFIG_KGDB_LOW_LEVEL_TRAP
if (kgdb_ll_trap(DIE_INT3, "int3", regs, error_code, X86_TRAP_BP,
SIGTRAP) == NOTIFY_STOP)
@@ -460,33 +544,20 @@ dotraplinkage void notrace do_int3(struct pt_regs *regs, long error_code)
preempt_conditional_cli(regs);
debug_stack_usage_dec();
exit:
- exception_exit(prev_state);
+ ist_exit(regs, prev_state);
}
NOKPROBE_SYMBOL(do_int3);

#ifdef CONFIG_X86_64
/*
- * Help handler running on IST stack to switch back to user stack
- * for scheduling or signal handling. The actual stack switch is done in
- * entry.S
+ * Help handler running on IST stack to switch off the IST stack if the
+ * interrupted code was in user mode. The actual stack switch is done in
+ * entry_64.S
*/
asmlinkage __visible notrace struct pt_regs *sync_regs(struct pt_regs *eregs)
{
- struct pt_regs *regs = eregs;
- /* Did already sync */
- if (eregs == (struct pt_regs *)eregs->sp)
- ;
- /* Exception from user space */
- else if (user_mode(eregs))
- regs = task_pt_regs(current);
- /*
- * Exception from kernel and interrupts are enabled. Move to
- * kernel process stack.
- */
- else if (eregs->flags & X86_EFLAGS_IF)
- regs = (struct pt_regs *)(eregs->sp -= sizeof(struct pt_regs));
- if (eregs != regs)
- *regs = *eregs;
+ struct pt_regs *regs = task_pt_regs(current);
+ *regs = *eregs;
return regs;
}
NOKPROBE_SYMBOL(sync_regs);
@@ -554,7 +625,7 @@ dotraplinkage void do_debug(struct pt_regs *regs, long error_code)
unsigned long dr6;
int si_code;

- prev_state = exception_enter();
+ prev_state = ist_enter(regs);

get_debugreg(dr6, 6);

@@ -629,7 +700,7 @@ dotraplinkage void do_debug(struct pt_regs *regs, long error_code)
debug_stack_usage_dec();

exit:
- exception_exit(prev_state);
+ ist_exit(regs, prev_state);
}
NOKPROBE_SYMBOL(do_debug);

diff --git a/arch/x86/vdso/Makefile b/arch/x86/vdso/Makefile
index 5a4affe025e8..09297c8e1fcd 100644
--- a/arch/x86/vdso/Makefile
+++ b/arch/x86/vdso/Makefile
@@ -205,4 +205,4 @@ $(vdso_img_insttargets): install_%: $(obj)/%.dbg $(MODLIB)/vdso FORCE
PHONY += vdso_install $(vdso_img_insttargets)
vdso_install: $(vdso_img_insttargets) FORCE

-clean-files := vdso32-syscall* vdso32-sysenter* vdso32-int80*
+clean-files := vdso32-syscall* vdso32-sysenter* vdso32-int80* vdso64*
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 7680fc275036..4c106fcc0d54 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -759,39 +759,71 @@ void rcu_irq_enter(void)
/**
* rcu_nmi_enter - inform RCU of entry to NMI context
*
- * If the CPU was idle with dynamic ticks active, and there is no
- * irq handler running, this updates rdtp->dynticks_nmi to let the
- * RCU grace-period handling know that the CPU is active.
+ * If the CPU was idle from RCU's viewpoint, update rdtp->dynticks and
+ * rdtp->dynticks_nmi_nesting to let the RCU grace-period handling know
+ * that the CPU is active. This implementation permits nested NMIs, as
+ * long as the nesting level does not overflow an int. (You will probably
+ * run out of stack space first.)
*/
void rcu_nmi_enter(void)
{
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
+ int incby = 2;

- if (rdtp->dynticks_nmi_nesting == 0 &&
- (atomic_read(&rdtp->dynticks) & 0x1))
- return;
- rdtp->dynticks_nmi_nesting++;
- smp_mb__before_atomic(); /* Force delay from prior write. */
- atomic_inc(&rdtp->dynticks);
- /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
- smp_mb__after_atomic(); /* See above. */
- WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
+ /* Complain about underflow. */
+ WARN_ON_ONCE(rdtp->dynticks_nmi_nesting < 0);
+
+ /*
+ * If idle from RCU viewpoint, atomically increment ->dynticks
+ * to mark non-idle and increment ->dynticks_nmi_nesting by one.
+ * Otherwise, increment ->dynticks_nmi_nesting by two. This means
+ * if ->dynticks_nmi_nesting is equal to one, we are guaranteed
+ * to be in the outermost NMI handler that interrupted an RCU-idle
+ * period (observation due to Andy Lutomirski).
+ */
+ if (!(atomic_read(&rdtp->dynticks) & 0x1)) {
+ smp_mb__before_atomic(); /* Force delay from prior write. */
+ atomic_inc(&rdtp->dynticks);
+ /* atomic_inc() before later RCU read-side crit sects */
+ smp_mb__after_atomic(); /* See above. */
+ WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
+ incby = 1;
+ }
+ rdtp->dynticks_nmi_nesting += incby;
+ barrier();
}

/**
* rcu_nmi_exit - inform RCU of exit from NMI context
*
- * If the CPU was idle with dynamic ticks active, and there is no
- * irq handler running, this updates rdtp->dynticks_nmi to let the
- * RCU grace-period handling know that the CPU is no longer active.
+ * If we are returning from the outermost NMI handler that interrupted an
+ * RCU-idle period, update rdtp->dynticks and rdtp->dynticks_nmi_nesting
+ * to let the RCU grace-period handling know that the CPU is back to
+ * being RCU-idle.
*/
void rcu_nmi_exit(void)
{
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);

- if (rdtp->dynticks_nmi_nesting == 0 ||
- --rdtp->dynticks_nmi_nesting != 0)
+ /*
+ * Check for ->dynticks_nmi_nesting underflow and bad ->dynticks.
+ * (We are exiting an NMI handler, so RCU better be paying attention
+ * to us!)
+ */
+ WARN_ON_ONCE(rdtp->dynticks_nmi_nesting <= 0);
+ WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
+
+ /*
+ * If the nesting level is not 1, the CPU wasn't RCU-idle, so
+ * leave it in non-RCU-idle state.
+ */
+ if (rdtp->dynticks_nmi_nesting != 1) {
+ rdtp->dynticks_nmi_nesting -= 2;
return;
+ }
+
+ /* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
+ rdtp->dynticks_nmi_nesting = 0;
/* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
smp_mb__before_atomic(); /* See above. */
atomic_inc(&rdtp->dynticks);