| Message ID | 20201022222701.887660-7-ira.weiny@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | PKS: Add Protection Keys Supervisor (PKS) support | expand |
On Thu, Oct 22 2020 at 15:26, ira weiny wrote: > From: Thomas Gleixner <tglx@linutronix.de> > > Lockdep state handling on NMI enter and exit is nothing specific to X86. It's > not any different on other architectures. Also the extra state type is not > necessary, irqentry_state_t can carry the necessary information as well. > > Move it to common code and extend irqentry_state_t to carry lockdep > state. This lacks something like: [ Ira: Made the states a union as they are mutually exclusive and added the missing kernel doc ] Hrm. > #ifndef irqentry_state > typedef struct irqentry_state { > - bool exit_rcu; > + union { > + bool exit_rcu; > + bool lockdep; > + }; > } irqentry_state_t; > #endif -E_NO_KERNELDOC Thanks, tglx
On Fri, Oct 23, 2020 at 11:50:11PM +0200, Thomas Gleixner wrote: > On Thu, Oct 22 2020 at 15:26, ira weiny wrote: > > > From: Thomas Gleixner <tglx@linutronix.de> > > > > Lockdep state handling on NMI enter and exit is nothing specific to X86. It's > > not any different on other architectures. Also the extra state type is not > > necessary, irqentry_state_t can carry the necessary information as well. > > > > Move it to common code and extend irqentry_state_t to carry lockdep > > state. > > This lacks something like: > > [ Ira: Made the states a union as they are mutually exclusive and added > the missing kernel doc ] Fair enough. done. > > Hrm. > > > #ifndef irqentry_state > > typedef struct irqentry_state { > > - bool exit_rcu; > > + union { > > + bool exit_rcu; > > + bool lockdep; > > + }; > > } irqentry_state_t; > > #endif > > -E_NO_KERNELDOC Adding: Paul McKenney I'm happy to write something but I'm very unfamiliar with this code. So I'm getting confused what exactly exit_rcu is flagging. I can see that exit_rcu is a bad name for the state used in irqentry_nmi_[enter|exit](). Furthermore, I see why 'lockdep' is a better name. But similar lockdep handling is used in irqentry_exit() if exit_rcu is true... Given my limited knowledge; here is my proposed text: /** * struct irqentry_state - Opaque object for exception state storage * @exit_rcu: Used exclusively in the irqentry_*() calls; tracks if the * exception hit the idle task which requires special handling, * including calling rcu_irq_exit(), when the exception exits. * @lockdep: Used exclusively in the irqentry_nmi_*() calls; ensures lockdep * tracking is maintained if hardirqs were already enabled * * This opaque object is filled in by the irqentry_*_enter() functions and * should be passed back into the corresponding irqentry_*_exit() functions * when the exception is complete. * * Callers of irqentry_*_[enter|exit]() should consider this structure opaque * and all members private. Descriptions of the members are provided to aid in * the maintenance of the irqentry_*() functions. */ Perhaps Paul can enlighten me on how exit_rcu is used beyond just flagging a call to rcu_irq_exit()? Why do we call lockdep_hardirqs_off() only when in the idle task? That implies that regs_irqs_disabled() can only be false if we were in the idle task to match up the lockdep on/off calls. This does not make sense to me because why do we need the extra check for exit_rcu? I'm still trying to understand when regs_irqs_disabled() is false. } else if (!regs_irqs_disabled(regs)) { ... } else { /* * IRQ flags state is correct already. Just tell RCU if it * was not watching on entry. */ if (state.exit_rcu) rcu_irq_exit(); } Also, the comment in irqentry_enter() refers to irq_enter_from_user_mode() which does not seem to exist anymore. So I'm not sure what careful sequence it is referring to. /* * If RCU is not watching then the same careful * sequence vs. lockdep and tracing is required * as in irq_enter_from_user_mode(). */ ? Ira
On Tue, Oct 27 2020 at 00:07, Ira Weiny wrote: > On Fri, Oct 23, 2020 at 11:50:11PM +0200, Thomas Gleixner wrote: >> > #ifndef irqentry_state >> > typedef struct irqentry_state { >> > - bool exit_rcu; >> > + union { >> > + bool exit_rcu; >> > + bool lockdep; >> > + }; >> > } irqentry_state_t; >> > #endif >> >> -E_NO_KERNELDOC > > Adding: Paul McKenney > > I'm happy to write something but I'm very unfamiliar with this code. So I'm > getting confused what exactly exit_rcu is flagging. > > I can see that exit_rcu is a bad name for the state used in > irqentry_nmi_[enter|exit](). Furthermore, I see why 'lockdep' is a better > name. But similar lockdep handling is used in irqentry_exit() if exit_rcu is > true... No, it's not similar at all. Lockdep state vs. interrupts and regular exceptions is always consistent. In the NMI case, that's not guaranteed because of local_irq_disable() arch_local_irq_disable() <- NMI race window trace_hardirqs_off() same the other way round local_irq_enable() trace_hardirqs_on() <- NMI race window arch_local_irq_enable() IOW, the hardware state and the lockdep state are not consistent. > /** > * struct irqentry_state - Opaque object for exception state storage > * @exit_rcu: Used exclusively in the irqentry_*() calls; tracks if the > * exception hit the idle task which requires special handling, > * including calling rcu_irq_exit(), when the exception > exits. calls; signals whether the exit path has to invoke rcu_irq_exit(). > * @lockdep: Used exclusively in the irqentry_nmi_*() calls; ensures lockdep > * tracking is maintained if hardirqs were already enabled ensures that lockdep state is restored correctly on exit from nmi. > * > * This opaque object is filled in by the irqentry_*_enter() functions and > * should be passed back into the corresponding irqentry_*_exit() > functions s/should/must/ > * when the exception is complete. > * > * Callers of irqentry_*_[enter|exit]() should consider this structure > opaque s/should/must/ > * and all members private. Descriptions of the members are provided to aid in > * the maintenance of the irqentry_*() functions. > */ > > Perhaps Paul can enlighten me on how exit_rcu is used beyond just flagging a > call to rcu_irq_exit()? I can do that as well :) The only purpose is to invoke rcu_irq_exit() conditionally. > Why do we call lockdep_hardirqs_off() only when in the idle task? That implies > that regs_irqs_disabled() can only be false if we were in the idle task to > match up the lockdep on/off calls. You're reading the code slightly wrong. > This does not make sense to me because why do we need the extra check > for exit_rcu? I'm still trying to understand when regs_irqs_disabled() is false. It's false when the interrupted context had interrupts enabled. So we have the following scenarios: Usermode Idletask irqs enabled RCU entry RCU exit Y N Y Y Y N N Y N N N N N N N N Y Y Y Y N Y N Y Y Now you might wonder about irqs enabled/disabled. This code is not only used for interrupts (device, ipi, local timer...) where interrupts are obviously enabled, it's also used for exception entry/exit. You can have e.g. pagefaults in interrupt disabled regions. > Also, the comment in irqentry_enter() refers to irq_enter_from_user_mode() which > does not seem to exist anymore. So I'm not sure what careful sequence it is > referring to. That was renamed to irqentry_enter_from_user_mode() and the comment was not updated. Sorry for leaving this hard to solve puzzle around. Thanks, tglx
diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c index 870efeec8bda..18d8f17f755c 100644 --- a/arch/x86/entry/common.c +++ b/arch/x86/entry/common.c @@ -209,40 +209,6 @@ SYSCALL_DEFINE0(ni_syscall) return -ENOSYS; } -noinstr bool idtentry_enter_nmi(struct pt_regs *regs) -{ - bool irq_state = lockdep_hardirqs_enabled(); - - __nmi_enter(); - lockdep_hardirqs_off(CALLER_ADDR0); - lockdep_hardirq_enter(); - rcu_nmi_enter(); - - instrumentation_begin(); - trace_hardirqs_off_finish(); - ftrace_nmi_enter(); - instrumentation_end(); - - return irq_state; -} - -noinstr void idtentry_exit_nmi(struct pt_regs *regs, bool restore) -{ - instrumentation_begin(); - ftrace_nmi_exit(); - if (restore) { - trace_hardirqs_on_prepare(); - lockdep_hardirqs_on_prepare(CALLER_ADDR0); - } - instrumentation_end(); - - rcu_nmi_exit(); - lockdep_hardirq_exit(); - if (restore) - lockdep_hardirqs_on(CALLER_ADDR0); - __nmi_exit(); -} - #ifdef CONFIG_XEN_PV #ifndef CONFIG_PREEMPTION /* diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h index b2442eb0ac2f..247a60a47331 100644 --- a/arch/x86/include/asm/idtentry.h +++ b/arch/x86/include/asm/idtentry.h @@ -11,9 +11,6 @@ #include <asm/irq_stack.h> -bool idtentry_enter_nmi(struct pt_regs *regs); -void idtentry_exit_nmi(struct pt_regs *regs, bool irq_state); - /** * DECLARE_IDTENTRY - Declare functions for simple IDT entry points * No error code pushed by hardware diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c index 1c08cb9eb9f6..eb3338c0bbc1 100644 --- a/arch/x86/kernel/cpu/mce/core.c +++ b/arch/x86/kernel/cpu/mce/core.c @@ -1983,7 +1983,7 @@ void (*machine_check_vector)(struct pt_regs *) = unexpected_machine_check; static __always_inline void exc_machine_check_kernel(struct pt_regs *regs) { - bool irq_state; + irqentry_state_t irq_state; WARN_ON_ONCE(user_mode(regs)); @@ -1995,7 +1995,7 @@ static __always_inline void exc_machine_check_kernel(struct pt_regs *regs) mce_check_crashing_cpu()) return; - irq_state = idtentry_enter_nmi(regs); + irq_state = irqentry_nmi_enter(regs); /* * The call targets are marked noinstr, but objtool can't figure * that out because it's an indirect call. Annotate it. @@ -2006,7 +2006,7 @@ static __always_inline void exc_machine_check_kernel(struct pt_regs *regs) if (regs->flags & X86_EFLAGS_IF) trace_hardirqs_on_prepare(); instrumentation_end(); - idtentry_exit_nmi(regs, irq_state); + irqentry_nmi_exit(regs, irq_state); } static __always_inline void exc_machine_check_user(struct pt_regs *regs) diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c index 4bc77aaf1303..bf250a339655 100644 --- a/arch/x86/kernel/nmi.c +++ b/arch/x86/kernel/nmi.c @@ -475,7 +475,7 @@ static DEFINE_PER_CPU(unsigned long, nmi_dr7); DEFINE_IDTENTRY_RAW(exc_nmi) { - bool irq_state; + irqentry_state_t irq_state; /* * Re-enable NMIs right here when running as an SEV-ES guest. This might @@ -502,14 +502,14 @@ DEFINE_IDTENTRY_RAW(exc_nmi) this_cpu_write(nmi_dr7, local_db_save()); - irq_state = idtentry_enter_nmi(regs); + irq_state = irqentry_nmi_enter(regs); inc_irq_stat(__nmi_count); if (!ignore_nmis) default_do_nmi(regs); - idtentry_exit_nmi(regs, irq_state); + irqentry_nmi_exit(regs, irq_state); local_db_restore(this_cpu_read(nmi_dr7)); diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index 3c70fb34028b..bffbbe29fc8c 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -405,7 +405,7 @@ DEFINE_IDTENTRY_DF(exc_double_fault) } #endif - idtentry_enter_nmi(regs); + irqentry_nmi_enter(regs); instrumentation_begin(); notify_die(DIE_TRAP, str, regs, error_code, X86_TRAP_DF, SIGSEGV); @@ -651,12 +651,13 @@ DEFINE_IDTENTRY_RAW(exc_int3) instrumentation_end(); irqentry_exit_to_user_mode(regs); } else { - bool irq_state = idtentry_enter_nmi(regs); + irqentry_state_t irq_state = irqentry_nmi_enter(regs); + instrumentation_begin(); if (!do_int3(regs)) die("int3", regs, 0); instrumentation_end(); - idtentry_exit_nmi(regs, irq_state); + irqentry_nmi_exit(regs, irq_state); } } @@ -864,7 +865,7 @@ static __always_inline void exc_debug_kernel(struct pt_regs *regs, * includes the entry stack is excluded for everything. */ unsigned long dr7 = local_db_save(); - bool irq_state = idtentry_enter_nmi(regs); + irqentry_state_t irq_state = irqentry_nmi_enter(regs); instrumentation_begin(); /* @@ -907,7 +908,7 @@ static __always_inline void exc_debug_kernel(struct pt_regs *regs, regs->flags &= ~X86_EFLAGS_TF; out: instrumentation_end(); - idtentry_exit_nmi(regs, irq_state); + irqentry_nmi_exit(regs, irq_state); local_db_restore(dr7); } @@ -925,7 +926,7 @@ static __always_inline void exc_debug_user(struct pt_regs *regs, /* * NB: We can't easily clear DR7 here because - * idtentry_exit_to_usermode() can invoke ptrace, schedule, access + * irqentry_exit_to_usermode() can invoke ptrace, schedule, access * user memory, etc. This means that a recursive #DB is possible. If * this happens, that #DB will hit exc_debug_kernel() and clear DR7. * Since we're not on the IST stack right now, everything will be diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h index 474f29638d2c..47f9a0658acf 100644 --- a/include/linux/entry-common.h +++ b/include/linux/entry-common.h @@ -342,7 +342,10 @@ void irqentry_exit_to_user_mode(struct pt_regs *regs); #ifndef irqentry_state typedef struct irqentry_state { - bool exit_rcu; + union { + bool exit_rcu; + bool lockdep; + }; } irqentry_state_t; #endif @@ -402,4 +405,23 @@ void irqentry_exit_cond_resched(void); */ void noinstr irqentry_exit(struct pt_regs *regs, irqentry_state_t state); +/** + * irqentry_nmi_enter - Handle NMI entry + * @regs: Pointer to currents pt_regs + * + * Similar to irqentry_enter() but taking care of the NMI constraints. + */ +irqentry_state_t noinstr irqentry_nmi_enter(struct pt_regs *regs); + +/** + * irqentry_nmi_exit - Handle return from NMI handling + * @regs: Pointer to pt_regs (NMI entry regs) + * @irq_state: Return value from matching call to irqentry_nmi_enter() + * + * Last action before returning to the low level assmenbly code. + * + * Counterpart to irqentry_nmi_enter(). + */ +void noinstr irqentry_nmi_exit(struct pt_regs *regs, irqentry_state_t irq_state); + #endif diff --git a/kernel/entry/common.c b/kernel/entry/common.c index 0a1e20f8d4e8..5cc2e4174d7c 100644 --- a/kernel/entry/common.c +++ b/kernel/entry/common.c @@ -398,3 +398,39 @@ noinstr void irqentry_exit(struct pt_regs *regs, irqentry_state_t state) rcu_irq_exit(); } } + +irqentry_state_t noinstr irqentry_nmi_enter(struct pt_regs *regs) +{ + irqentry_state_t irq_state; + + irq_state.lockdep = lockdep_hardirqs_enabled(); + + __nmi_enter(); + lockdep_hardirqs_off(CALLER_ADDR0); + lockdep_hardirq_enter(); + rcu_nmi_enter(); + + instrumentation_begin(); + trace_hardirqs_off_finish(); + ftrace_nmi_enter(); + instrumentation_end(); + + return irq_state; +} + +void noinstr irqentry_nmi_exit(struct pt_regs *regs, irqentry_state_t irq_state) +{ + instrumentation_begin(); + ftrace_nmi_exit(); + if (irq_state.lockdep) { + trace_hardirqs_on_prepare(); + lockdep_hardirqs_on_prepare(CALLER_ADDR0); + } + instrumentation_end(); + + rcu_nmi_exit(); + lockdep_hardirq_exit(); + if (irq_state.lockdep) + lockdep_hardirqs_on(CALLER_ADDR0); + __nmi_exit(); +}