From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Woodhouse Subject: [PATCH v2] kvm/x86: Inform RCU of quiescent state when entering guest mode Date: Wed, 11 Jul 2018 19:01:01 +0100 Message-ID: <20180711180101.3711464-1-dwmw2@infradead.org> References: <20180711174843.GX3593@linux.vnet.ibm.com> To: peterz@infradead.org, mhillenb@amazon.de, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, paulmck@linux.vnet.ibm.com Return-path: In-Reply-To: <20180711174843.GX3593@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org From: David Woodhouse RCU can spend long periods of time waiting for a CPU which is actually in KVM guest mode, entirely pointlessly. Treat it like the idle and userspace modes, and don't wait for it. Signed-off-by: David Woodhouse --- arch/x86/kvm/x86.c | 2 ++ include/linux/rcupdate.h | 7 +++++++ kernel/rcu/tree.c | 2 ++ 3 files changed, 11 insertions(+) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 0046aa70205a..b0c82f70afa7 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -7458,7 +7458,9 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) vcpu->arch.switch_db_regs &= ~KVM_DEBUGREG_RELOAD; } + rcu_kvm_enter(); kvm_x86_ops->run(vcpu); + rcu_kvm_exit(); /* * Do this here before restoring debug registers on the host. And diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 65163aa0bb04..1325f9d9ce00 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -212,6 +212,13 @@ do { \ #error "Unknown RCU implementation specified to kernel configuration" #endif +/* + * These are currently identical to the _idle_ versions but let's + * explicitly have separate copies to keep Paul honest in future. + */ +static inline void rcu_kvm_enter(void) { rcu_idle_enter(); } +static inline void rcu_kvm_exit(void) { rcu_idle_exit(); } + /* * The init_rcu_head_on_stack() and destroy_rcu_head_on_stack() calls * are needed for dynamic initialization and destruction of rcu_head diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index aa7cade1b9f3..d38c381bf4e3 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -760,6 +760,7 @@ void rcu_idle_enter(void) lockdep_assert_irqs_disabled(); rcu_eqs_enter(false); } +EXPORT_SYMBOL_GPL(rcu_idle_enter); #ifdef CONFIG_NO_HZ_FULL /** @@ -913,6 +914,7 @@ void rcu_idle_exit(void) rcu_eqs_exit(false); local_irq_restore(flags); } +EXPORT_SYMBOL_GPL(rcu_idle_exit); #ifdef CONFIG_NO_HZ_FULL /** -- 2.17.1