From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with SMTP id 5F2816B004A for ; Thu, 7 Oct 2010 14:03:52 -0400 (EDT) Date: Thu, 7 Oct 2010 20:03:40 +0200 From: Gleb Natapov Subject: Re: [PATCH v6 08/12] Handle async PF in a guest. Message-ID: <20101007180340.GI2397@redhat.com> References: <1286207794-16120-1-git-send-email-gleb@redhat.com> <1286207794-16120-9-git-send-email-gleb@redhat.com> <4CADC6C3.3040305@redhat.com> <20101007171418.GA2397@redhat.com> <4CAE00CB.1070400@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4CAE00CB.1070400@redhat.com> Sender: owner-linux-mm@kvack.org To: Avi Kivity 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 Thu, Oct 07, 2010 at 07:18:03PM +0200, Avi Kivity wrote: > On 10/07/2010 07:14 PM, Gleb Natapov wrote: > >On Thu, Oct 07, 2010 at 03:10:27PM +0200, Avi Kivity wrote: > >> 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? > >> > >Host side keeps track of outstanding apfs and will not send apf for the > >same phys address twice. It will halt vcpu instead. > > What about different pages, running the scheduler code? > We can get couple of nested apfs, just like we can get nested interrupts. Since scheduler disables preemption second apf will halt. > Oh, and we'll run the scheduler recursively. > As rick said scheduler disables preemption. And this is actually first thing it does. Otherwise any interrupt may cause recursive scheduler invocation. -- Gleb. -- 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