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=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,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 C55A8C3A59C for ; Thu, 15 Aug 2019 19:33:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 99B4120656 for ; Thu, 15 Aug 2019 19:33:09 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=ziepe.ca header.i=@ziepe.ca header.b="DSQnzP2b" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732567AbfHOTdJ (ORCPT ); Thu, 15 Aug 2019 15:33:09 -0400 Received: from mail-qt1-f194.google.com ([209.85.160.194]:42858 "EHLO mail-qt1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732499AbfHOTdE (ORCPT ); Thu, 15 Aug 2019 15:33:04 -0400 Received: by mail-qt1-f194.google.com with SMTP id t12so3543093qtp.9 for ; Thu, 15 Aug 2019 12:33:03 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ziepe.ca; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:content-transfer-encoding:in-reply-to :user-agent; bh=d/Vs2YH0f5xNou4jHOnIZOohEAfDIJUopBMHuRVrEaM=; b=DSQnzP2boVVz05frK9Rf9m+2jw7zFPx+9AUXj2jqSyufMDNrAKls4vo+Fb+WrAEgvO ktfk/TjL4ijraP2CEooza64EfLjaFdcqjeQ5Vv3suWLQE3AFJsd5YcPid89lanEu0ZoG VOQYC/bNeGf1IZi2CVdyacQhQw7JiSZnXckYhCGW/PB/p43g8HasbOXkyAfk/T5vpF3D xiyWjGC5nu7KpcLH5DDONB00uambPQIgUVk3jQbczWBzrPFHJZNpEMI+ZlEgjUg+75rH LjzpVx3i2jLsC6X0ifOF/LcBrXk/+s6IlAd5gRScNQG9jSmLI4mn6ct4mUNoFB6ybWFo /qdg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:content-transfer-encoding :in-reply-to:user-agent; bh=d/Vs2YH0f5xNou4jHOnIZOohEAfDIJUopBMHuRVrEaM=; b=r5nE5B33COTMUnM1WtTDEeqhU5x6rcPE6C2UUxInWaNEE+AcL0kWwwj9d+kttTeJjf haxFEsvGjpGv6iJl7kzkueLgAGiMP738M72uQsJGNKbYwy4U7WNytoyWB+1Sj9ru3bir TNGgCidEt3V9TzXAfaE7zYFvD8dLzDs9RtnOuz5MOuH8df0OyhtzDRA04RkHYOTunGyW gqUQKrZ3722Oa5jAKu2LWSEhyUQTDciQwRSyvCp1w2z+4QuS2Avq0aV3G4is+X5ZzlAg SFq4xJ8FAsO2XJ+lKCv6/qvIPxeppx0zKlrLRCQahie/AnquUrcEwXsCoGoTnxOI5j+t 8bQA== X-Gm-Message-State: APjAAAVI6zF8HMgrpo0RDYbt60ekM0FeVor4WzA3si6AfL43pZAkdHA6 VsThmP+zi0CQTYtBvneHuqu8bQ== X-Google-Smtp-Source: APXvYqzizPYl2LrtkxXjbmjRPnD30yqIwKDY6KgNsz0NbhIueWjJnIkysTmtYLAdQWA6iei+yUmzJQ== X-Received: by 2002:ac8:5343:: with SMTP id d3mr5516461qto.50.1565897583402; Thu, 15 Aug 2019 12:33:03 -0700 (PDT) Received: from ziepe.ca (hlfxns017vw-156-34-55-100.dhcp-dynamic.fibreop.ns.bellaliant.net. [156.34.55.100]) by smtp.gmail.com with ESMTPSA id s4sm1862094qkb.130.2019.08.15.12.33.02 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 15 Aug 2019 12:33:03 -0700 (PDT) Received: from jgg by mlx.ziepe.ca with local (Exim 4.90_1) (envelope-from ) id 1hyLUc-0008Aa-AF; Thu, 15 Aug 2019 16:33:02 -0300 Date: Thu, 15 Aug 2019 16:33:02 -0300 From: Jason Gunthorpe To: Jason Wang Cc: "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: <20190815193302.GT21596@ziepe.ca> 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> <74838e61-3a5e-0f51-2092-f4a16d144b45@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <74838e61-3a5e-0f51-2092-f4a16d144b45@redhat.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Thu, Aug 15, 2019 at 11:26:46AM +0800, Jason Wang wrote: > > On 2019/8/13 下午7:57, 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 > > > My understanding is __get_user_pages_fast() assumes caller can fail or have > fallback. And we have graceful fallback to copy_{to|from}_user(). My point is that if you can fall back to copy_user then it is weird to call the special non-sleeping GUP under a spinlock. AFAIK the only reason this is done is because of the way the notifier is being locked... Jason