From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail191.messagelabs.com (mail191.messagelabs.com [216.82.242.19]) by kanga.kvack.org (Postfix) with SMTP id 7BF356B004A for ; Thu, 7 Oct 2010 09:10:56 -0400 (EDT) Message-ID: <4CADC6C3.3040305@redhat.com> Date: Thu, 07 Oct 2010 15:10:27 +0200 From: Avi Kivity MIME-Version: 1.0 Subject: Re: [PATCH v6 08/12] Handle async PF in a guest. References: <1286207794-16120-1-git-send-email-gleb@redhat.com> <1286207794-16120-9-git-send-email-gleb@redhat.com> In-Reply-To: <1286207794-16120-9-git-send-email-gleb@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Gleb Natapov Cc: kvm@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, mingo@elte.hu, a.p.zijlstra@chello.nl, tglx@linutronix.de, hpa@zytor.com, riel@redhat.com, cl@linux-foundation.org, mtosatti@redhat.com List-ID: On 10/04/2010 05:56 PM, Gleb Natapov wrote: > When async PF capability is detected hook up special page fault handler > that will handle async page fault events and bypass other page faults to > regular page fault handler. Also add async PF handling to nested SVM > emulation. Async PF always generates exit to L1 where vcpu thread will > be scheduled out until page is available. > Please separate guest and host changes. > +void kvm_async_pf_task_wait(u32 token) > +{ > + u32 key = hash_32(token, KVM_TASK_SLEEP_HASHBITS); > + struct kvm_task_sleep_head *b =&async_pf_sleepers[key]; > + struct kvm_task_sleep_node n, *e; > + DEFINE_WAIT(wait); > + > + spin_lock(&b->lock); > + e = _find_apf_task(b, token); > + if (e) { > + /* dummy entry exist -> wake up was delivered ahead of PF */ > + hlist_del(&e->link); > + kfree(e); > + spin_unlock(&b->lock); > + return; > + } > + > + n.token = token; > + n.cpu = smp_processor_id(); > + init_waitqueue_head(&n.wq); > + hlist_add_head(&n.link,&b->list); > + spin_unlock(&b->lock); > + > + for (;;) { > + prepare_to_wait(&n.wq,&wait, TASK_UNINTERRUPTIBLE); > + if (hlist_unhashed(&n.link)) > + break; > + local_irq_enable(); Suppose we take another apf here. And another, and another (for different pages, while executing schedule()). What's to prevent kernel stack overflow? > + schedule(); > + local_irq_disable(); > + } > + finish_wait(&n.wq,&wait); > + > + return; > +} > +EXPORT_SYMBOL_GPL(kvm_async_pf_task_wait); > + I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org