From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 72FF8C32750 for ; Tue, 13 Aug 2019 16:41:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4433120651 for ; Tue, 13 Aug 2019 16:41:10 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="MG4m3VyH" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728228AbfHMQlI (ORCPT ); Tue, 13 Aug 2019 12:41:08 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:48470 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726802AbfHMQlI (ORCPT ); Tue, 13 Aug 2019 12:41:08 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=7HlWwLFzCOZ7QQzVMV27bTyBbuYurJG67TdGyoRs0fo=; b=MG4m3VyHxaBDt/hiB/6nJ65WT b9Emowpcs+4HzgPIxmnraEW2+NFya3pXsJqx0S8UbklD6unAQ440ZPfk/zs9iuo2ojw7YF3XpQNqU iWQLBbQAx3tKFWzwOmMqGdgMqVC4dkSROVMEOa+09M/2vCct8HDQwhsXjUpVAkljtlKuwE1fG20VN HJxyfbbJrM+FgMUi0BFqDeZQGMvItaJU5kREdwtYCZTrNVG98Ys6PLgUbVWzroCggRKDKodRocPuB 2a1h94b6GBDUPat/0+u1o1LGSsIScGeECk/QhTkMpWqbOxzKJ6DY4oAmPhzadn3POONzyq6oDZlyI cx9F5vrwg==; Received: from hch by bombadil.infradead.org with local (Exim 4.92 #3 (Red Hat Linux)) id 1hxZr7-0000hw-Tj; Tue, 13 Aug 2019 16:41:05 +0000 Date: Tue, 13 Aug 2019 09:41:05 -0700 From: Christoph Hellwig To: Jason Gunthorpe Cc: Jason Wang , "Michael S. Tsirkin" , kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH V5 0/9] Fixes for vhost metadata acceleration Message-ID: <20190813164105.GD22640@infradead.org> References: <20190809054851.20118-1-jasowang@redhat.com> <20190810134948-mutt-send-email-mst@kernel.org> <360a3b91-1ac5-84c0-d34b-a4243fa748c4@redhat.com> <20190812054429-mutt-send-email-mst@kernel.org> <20190812130252.GE24457@ziepe.ca> <9a9641fe-b48f-f32a-eecc-af9c2f4fbe0e@redhat.com> <20190813115707.GC29508@ziepe.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190813115707.GC29508@ziepe.ca> User-Agent: Mutt/1.11.4 (2019-03-13) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 13, 2019 at 08:57:07AM -0300, Jason Gunthorpe wrote: > On Tue, Aug 13, 2019 at 04:31:07PM +0800, Jason Wang wrote: > > > What kind of issues do you see? Spinlock is to synchronize GUP with MMU > > notifier in this series. > > A GUP that can't sleep can't pagefault which makes it a really weird > pattern get_user_pages/get_user_pages_fast must not be called under a spinlock. We have the somewhat misnamed __get_user_page_fast that just does a lookup for existing pages and never faults for a few places that need to do that lookup from contexts where we can't sleep.