From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751735Ab2LDCf3 (ORCPT ); Mon, 3 Dec 2012 21:35:29 -0500 Received: from e28smtp04.in.ibm.com ([122.248.162.4]:55632 "EHLO e28smtp04.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751705Ab2LDCf1 (ORCPT ); Mon, 3 Dec 2012 21:35:27 -0500 Message-ID: <1354588513.2649.10.camel@ThinkPad-T5421.cn.ibm.com> Subject: [ PATCH] Add rcu user eqs exception hooks for async page fault From: Li Zhong To: Gleb Natapov Cc: Frederic Weisbecker , linux-next list , LKML , paulmck@linux.vnet.ibm.com, sasha.levin@oracle.com, avi@redhat.com Date: Tue, 04 Dec 2012 10:35:13 +0800 In-Reply-To: <20121203095708.GO8731@redhat.com> References: <1353993325.14050.49.camel@ThinkPad-T5421.cn.ibm.com> <1354090704.3054.13.camel@ThinkPad-T5421.cn.ibm.com> <20121128135345.GG928@redhat.com> <20121129110717.GA9711@redhat.com> <1354267121.2552.65.camel@ThinkPad-T5421.cn.ibm.com> <20121203095708.GO8731@redhat.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3-0ubuntu6 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12120402-5564-0000-0000-0000059F478D Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This patch adds user eqs exception hooks for async page fault page not present code path, to exit the user eqs and re-enter it as necessary. Async page fault is different from other exceptions that it may be triggered from idle process, so we still need rcu_irq_enter() and rcu_irq_exit() to exit cpu idle eqs when needed, to protect the code that needs use rcu. As Frederic pointed out it would be safest and simplest to protect the whole kvm_async_pf_task_wait(). Otherwise, "we need to check all the code there deeply for potential RCU uses and ensure it will never be extended later to use RCU.". However, We'd better re-enter the cpu idle eqs if we get the exception in cpu idle eqs, by calling rcu_irq_exit() before native_safe_halt(). So the patch does what Frederic suggested for rcu_irq_*() API usage here, except that I moved the rcu_irq_*() pair originally in do_async_page_fault() into kvm_async_pf_task_wait(). That's because, I think it's better to have rcu_irq_*() pairs to be in one function ( rcu_irq_exit() after rcu_irq_enter() ), especially here, kvm_async_pf_task_wait() has other callers, which might cause rcu_irq_exit() be called without a matching rcu_irq_enter() before it, which is illegal if the cpu happens to be in rcu idle state. Signed-off-by: Li Zhong --- arch/x86/kernel/kvm.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c index 08b973f..e99af60 100644 --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -43,6 +43,7 @@ #include #include #include +#include static int kvmapf = 1; @@ -121,6 +122,8 @@ void kvm_async_pf_task_wait(u32 token) struct kvm_task_sleep_node n, *e; DEFINE_WAIT(wait); + rcu_irq_enter(); + spin_lock(&b->lock); e = _find_apf_task(b, token); if (e) { @@ -128,6 +131,8 @@ void kvm_async_pf_task_wait(u32 token) hlist_del(&e->link); kfree(e); spin_unlock(&b->lock); + + rcu_irq_exit(); return; } @@ -152,13 +157,16 @@ void kvm_async_pf_task_wait(u32 token) /* * We cannot reschedule. So halt. */ + rcu_irq_exit(); native_safe_halt(); + rcu_irq_enter(); local_irq_disable(); } } if (!n.halted) finish_wait(&n.wq, &wait); + rcu_irq_exit(); return; } EXPORT_SYMBOL_GPL(kvm_async_pf_task_wait); @@ -252,10 +260,10 @@ do_async_page_fault(struct pt_regs *regs, unsigned long error_code) break; case KVM_PV_REASON_PAGE_NOT_PRESENT: /* page is swapped out by the host. */ - rcu_irq_enter(); + exception_enter(regs); exit_idle(); kvm_async_pf_task_wait((u32)read_cr2()); - rcu_irq_exit(); + exception_exit(regs); break; case KVM_PV_REASON_PAGE_READY: rcu_irq_enter(); -- 1.7.11.4