From ebaac1736245e78109cd47d453a86a18dcfc94b8 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Wed, 15 Jun 2016 15:09:28 +0200 Subject: context_tracking: move rcu_virt_note_context_switch out of kvm_host.h Make kvm_guest_{enter,exit} and __kvm_guest_{enter,exit} trivial wrappers around the code in context_tracking.h. Name the context_tracking.h functions consistently with what those for kernel<->user switch. Cc: Andy Lutomirski Cc: Peter Zijlstra Cc: H. Peter Anvin Cc: Ingo Molnar Cc: Thomas Gleixner Reviewed-by: Rik van Riel Signed-off-by: Paolo Bonzini --- include/linux/context_tracking.h | 38 ++++++++++++++++++++++++++++++++++---- 1 file changed, 34 insertions(+), 4 deletions(-) (limited to 'include/linux/context_tracking.h') diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h index d259274238db..ff4a32d24d56 100644 --- a/include/linux/context_tracking.h +++ b/include/linux/context_tracking.h @@ -84,7 +84,8 @@ static inline void context_tracking_init(void) { } #ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN -static inline void guest_enter(void) +/* must be called with irqs disabled */ +static inline void guest_enter_irqoff(void) { if (vtime_accounting_cpu_enabled()) vtime_guest_enter(current); @@ -93,9 +94,19 @@ static inline void guest_enter(void) if (context_tracking_is_enabled()) __context_tracking_enter(CONTEXT_GUEST); + + /* KVM does not hold any references to rcu protected data when it + * switches CPU into a guest mode. In fact switching to a guest mode + * is very similar to exiting to userspace from rcu point of view. In + * addition CPU may stay in a guest mode for quite a long time (up to + * one time slice). Lets treat guest mode as quiescent state, just like + * we do with user-mode execution. + */ + if (!context_tracking_cpu_is_enabled()) + rcu_virt_note_context_switch(smp_processor_id()); } -static inline void guest_exit(void) +static inline void guest_exit_irqoff(void) { if (context_tracking_is_enabled()) __context_tracking_exit(CONTEXT_GUEST); @@ -107,7 +118,7 @@ static inline void guest_exit(void) } #else -static inline void guest_enter(void) +static inline void guest_enter_irqoff(void) { /* * This is running in ioctl context so its safe @@ -116,9 +127,10 @@ static inline void guest_enter(void) */ vtime_account_system(current); current->flags |= PF_VCPU; + rcu_virt_note_context_switch(smp_processor_id()); } -static inline void guest_exit(void) +static inline void guest_exit_irqoff(void) { /* Flush the guest cputime we spent on the guest */ vtime_account_system(current); @@ -126,4 +138,22 @@ static inline void guest_exit(void) } #endif /* CONFIG_VIRT_CPU_ACCOUNTING_GEN */ +static inline void guest_enter(void) +{ + unsigned long flags; + + local_irq_save(flags); + guest_enter_irqoff(); + local_irq_restore(flags); +} + +static inline void guest_exit(void) +{ + unsigned long flags; + + local_irq_save(flags); + guest_exit_irqoff(); + local_irq_restore(flags); +} + #endif -- cgit v1.2.3 From 2e9d1e150abf88cb63e5d34ca286edbb95b4c53d Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Mon, 20 Jun 2016 16:58:29 +0200 Subject: x86/entry: Avoid interrupt flag save and restore Thanks to all the work that was done by Andy Lutomirski and others, enter_from_user_mode() and prepare_exit_to_usermode() are now called only with interrupts disabled. Let's provide them a version of user_enter()/user_exit() that skips saving and restoring the interrupt flag. On an AMD-based machine I tested this patch on, with force-enabled context tracking, the speed-up in system calls was 90 clock cycles or 6%, measured with the following simple benchmark: #include #include #include #include unsigned long rdtsc() { unsigned long result; asm volatile("rdtsc; shl $32, %%rdx; mov %%eax, %%eax\n" "or %%rdx, %%rax" : "=a" (result) : : "rdx"); return result; } int main() { unsigned long tsc1, tsc2; int pid = getpid(); int i; tsc1 = rdtsc(); for (i = 0; i < 100000000; i++) kill(pid, SIGWINCH); tsc2 = rdtsc(); printf("%ld\n", tsc2 - tsc1); } Signed-off-by: Paolo Bonzini Reviewed-by: Rik van Riel Reviewed-by: Andy Lutomirski Acked-by: Paolo Bonzini Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Josh Poimboeuf Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: kvm@vger.kernel.org Link: http://lkml.kernel.org/r/1466434712-31440-2-git-send-email-pbonzini@redhat.com Signed-off-by: Ingo Molnar --- arch/x86/entry/common.c | 4 ++-- include/linux/context_tracking.h | 15 +++++++++++++++ 2 files changed, 17 insertions(+), 2 deletions(-) (limited to 'include/linux/context_tracking.h') diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c index ec138e538c44..618bc61d35b7 100644 --- a/arch/x86/entry/common.c +++ b/arch/x86/entry/common.c @@ -43,7 +43,7 @@ static struct thread_info *pt_regs_to_thread_info(struct pt_regs *regs) __visible void enter_from_user_mode(void) { CT_WARN_ON(ct_state() != CONTEXT_USER); - user_exit(); + user_exit_irqoff(); } #else static inline void enter_from_user_mode(void) {} @@ -274,7 +274,7 @@ __visible inline void prepare_exit_to_usermode(struct pt_regs *regs) ti->status &= ~TS_COMPAT; #endif - user_enter(); + user_enter_irqoff(); } #define SYSCALL_EXIT_WORK_FLAGS \ diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h index d259274238db..d9aef2a0ec8e 100644 --- a/include/linux/context_tracking.h +++ b/include/linux/context_tracking.h @@ -31,6 +31,19 @@ static inline void user_exit(void) context_tracking_exit(CONTEXT_USER); } +/* Called with interrupts disabled. */ +static inline void user_enter_irqoff(void) +{ + if (context_tracking_is_enabled()) + __context_tracking_enter(CONTEXT_USER); + +} +static inline void user_exit_irqoff(void) +{ + if (context_tracking_is_enabled()) + __context_tracking_exit(CONTEXT_USER); +} + static inline enum ctx_state exception_enter(void) { enum ctx_state prev_ctx; @@ -69,6 +82,8 @@ static inline enum ctx_state ct_state(void) #else static inline void user_enter(void) { } static inline void user_exit(void) { } +static inline void user_enter_irqoff(void) { } +static inline void user_exit_irqoff(void) { } static inline enum ctx_state exception_enter(void) { return 0; } static inline void exception_exit(enum ctx_state prev_ctx) { } static inline enum ctx_state ct_state(void) { return CONTEXT_DISABLED; } -- cgit v1.2.3