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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 16FCDC7618B for ; Tue, 23 Jul 2019 15:02:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EAA152239F for ; Tue, 23 Jul 2019 15:02:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732908AbfGWPCr (ORCPT ); Tue, 23 Jul 2019 11:02:47 -0400 Received: from mail-qk1-f196.google.com ([209.85.222.196]:45542 "EHLO mail-qk1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730674AbfGWPCr (ORCPT ); Tue, 23 Jul 2019 11:02:47 -0400 Received: by mail-qk1-f196.google.com with SMTP id s22so31373744qkj.12 for ; Tue, 23 Jul 2019 08:02:47 -0700 (PDT) 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; bh=R5M2K4AjBjzXbSZ/zP6imFgwCWLsiDqliCyMwtU6WVA=; b=BpKdl5RDpagdQ2fQG+cPNUJ8jaBG8UnYMKAn19dqrzf8D+6JXQvTqNiALDd6HUoK8f 0iSaBR7HxfNzf7dKKvf6F54E12DBj6cbfyK97aTqqAjXksI1UCLzdAZTQw93uBZWRfKb 0Oi48nKdSyRJbMfB6PobKdLhegwQZ1lps/hETmtjs4UB1HYhsB4exP8Df+Uk1GPO+e4y N4Mwg7GN92dhdTD5v2jlkuD0zI9KPrW/xd4LDIhdHSvW9shafv5hYm7rm7VjlE7wFuSr Sk2rXTrNIhYGZHvxJ5wG5bxZ1WEwmxZV+PSNJe6QD6OGg+xXbQf/W7EAsk6T9svPtGHt x2FA== X-Gm-Message-State: APjAAAXpXxbGI2ie/+XxDBAzUzu5jlhGW0J7kZcDfPbvGlbTMdJvZGMN 4tTzNhsUE/Zu5NHOX1rvVqCD5Q== X-Google-Smtp-Source: APXvYqxzk6SWsTdinjKSsA/de1iMdf+1ZzQW/oUQt2F/o3dsQk8ga4tD5zxAx4DzheYaNy643xaKrA== X-Received: by 2002:ae9:e20c:: with SMTP id c12mr49989037qkc.210.1563894166621; Tue, 23 Jul 2019 08:02:46 -0700 (PDT) Received: from redhat.com (bzq-79-181-91-42.red.bezeqint.net. [79.181.91.42]) by smtp.gmail.com with ESMTPSA id s25sm18898787qkm.130.2019.07.23.08.02.39 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Tue, 23 Jul 2019 08:02:45 -0700 (PDT) Date: Tue, 23 Jul 2019 11:02:37 -0400 From: "Michael S. Tsirkin" To: Jason Wang Cc: syzbot , aarcange@redhat.com, akpm@linux-foundation.org, christian@brauner.io, davem@davemloft.net, ebiederm@xmission.com, elena.reshetova@intel.com, guro@fb.com, hch@infradead.org, james.bottomley@hansenpartnership.com, jglisse@redhat.com, keescook@chromium.org, ldv@altlinux.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-parisc@vger.kernel.org, luto@amacapital.net, mhocko@suse.com, mingo@kernel.org, namit@vmware.com, peterz@infradead.org, syzkaller-bugs@googlegroups.com, viro@zeniv.linux.org.uk, wad@chromium.org Subject: Re: WARNING in __mmdrop Message-ID: <20190723110219-mutt-send-email-mst@kernel.org> References: <20190721044615-mutt-send-email-mst@kernel.org> <75c43998-3a1c-676f-99ff-3d04663c3fcc@redhat.com> <20190722035657-mutt-send-email-mst@kernel.org> <20190723010156-mutt-send-email-mst@kernel.org> <124be1a2-1c53-8e65-0f06-ee2294710822@redhat.com> <20190723032800-mutt-send-email-mst@kernel.org> <20190723062221-mutt-send-email-mst@kernel.org> <9baa4214-67fd-7ad2-cbad-aadf90bbfc20@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <9baa4214-67fd-7ad2-cbad-aadf90bbfc20@redhat.com> Sender: linux-parisc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-parisc@vger.kernel.org On Tue, Jul 23, 2019 at 09:34:29PM +0800, Jason Wang wrote: > > On 2019/7/23 下午6:27, Michael S. Tsirkin wrote: > > > Yes, since there could be multiple co-current invalidation requests. We need > > > count them to make sure we don't pin wrong pages. > > > > > > > > > > I also wonder about ordering. kvm has this: > > > > /* > > > > * Used to check for invalidations in progress, of the pfn that is > > > > * returned by pfn_to_pfn_prot below. > > > > */ > > > > mmu_seq = kvm->mmu_notifier_seq; > > > > /* > > > > * Ensure the read of mmu_notifier_seq isn't reordered with PTE reads in > > > > * gfn_to_pfn_prot() (which calls get_user_pages()), so that we don't > > > > * risk the page we get a reference to getting unmapped before we have a > > > > * chance to grab the mmu_lock without mmu_notifier_retry() noticing. > > > > * > > > > * This smp_rmb() pairs with the effective smp_wmb() of the combination > > > > * of the pte_unmap_unlock() after the PTE is zapped, and the > > > > * spin_lock() in kvm_mmu_notifier_invalidate_() before > > > > * mmu_notifier_seq is incremented. > > > > */ > > > > smp_rmb(); > > > > > > > > does this apply to us? Can't we use a seqlock instead so we do > > > > not need to worry? > > > I'm not familiar with kvm MMU internals, but we do everything under of > > > mmu_lock. > > > > > > Thanks > > I don't think this helps at all. > > > > There's no lock between checking the invalidate counter and > > get user pages fast within vhost_map_prefetch. So it's possible > > that get user pages fast reads PTEs speculatively before > > invalidate is read. > > > > -- > > > In vhost_map_prefetch() we do: > >         spin_lock(&vq->mmu_lock); > >         ... > >         err = -EFAULT; >         if (vq->invalidate_count) >                 goto err; > >         ... > >         npinned = __get_user_pages_fast(uaddr->uaddr, npages, >                                         uaddr->write, pages); > >         ... > >         spin_unlock(&vq->mmu_lock); > > Is this not sufficient? > > Thanks So what orders __get_user_pages_fast wrt invalidate_count read? -- MST 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=-0.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 519EDC7618B for ; Tue, 23 Jul 2019 15:02:52 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 27D172239F for ; Tue, 23 Jul 2019 15:02:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="PEC/onSt" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 27D172239F Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=ZGUWzV541/ZxsWL9c0+p5/CmVs78zHFoTeV0N9VgSi0=; b=PEC/onSt7wMIhB +YI6kThwbplgb00IvaJBrz5QSsYbvp5JA91hKyUuHm3eMfbxbx9bWgXtnOYIQAAjkwewkbAhoAukj SHT1dkfwOuo+Xskwj9I0NRMqRbtO5bqYAHYevfVVggbzFYNJPVsRWEzV35o4TFJYdXHPGU/rufm9G NjszAwPH33BvjEK6Z8TxGIylfT3yjVOfr46d84M/lBPoY639hMBEcM5m20VpZa+PAr5iLrCAcaCwo iTk2ZshqyfPI3su6SPyrGbiVNFCF39i8MOndrZYilZQIv5Z5K5zP7xyIhAJCo3Vl2efZbJLjFYRRY E0shiYdG0fKi5c3VOmZA==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hpwJX-0000aj-QQ; Tue, 23 Jul 2019 15:02:51 +0000 Received: from mail-qk1-f196.google.com ([209.85.222.196]) by bombadil.infradead.org with esmtps (Exim 4.92 #3 (Red Hat Linux)) id 1hpwJT-0000Za-N5 for linux-arm-kernel@lists.infradead.org; Tue, 23 Jul 2019 15:02:49 +0000 Received: by mail-qk1-f196.google.com with SMTP id r21so31404385qke.2 for ; Tue, 23 Jul 2019 08:02:47 -0700 (PDT) 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; bh=R5M2K4AjBjzXbSZ/zP6imFgwCWLsiDqliCyMwtU6WVA=; b=e63AOmb6HSfRZxKZw9xDcwzAbAjChufhqedOiDgPNognJ5wEhrwwg3nQdaVWNZi3E0 O+IAqs0HqSdGqYmFUd3/bfHUXOPCBsGZrYDJltaIfOKkV17pQQ/tFgopiIOmGdlxmclu M/5lmkb6WlIgTZjifNVD+NbmJeczUxAgP3YVMFpmEqKbJDC/clr1NPkqLtd7JlkCObvY 9EPXn1KenqYUlt6mKjv8k8iXPA1JRgTuSrMXxnZuDo16JxGDFNmOkm10nMSL3P2I6Kdr DOLtmudOfbRA7bXAwjFPIdM5T6n9CW1phaam+GSxDin/Fmvr5OXL5Vv6x0mvEb/d1u6I zgTA== X-Gm-Message-State: APjAAAVrt5V/EBBHniJNTT+yFiDgsKd60SBnsxcVyEWLN9TcqS60c7Tn J845d4Q9gYFSRRz79lcJY0xpRA== X-Google-Smtp-Source: APXvYqxzk6SWsTdinjKSsA/de1iMdf+1ZzQW/oUQt2F/o3dsQk8ga4tD5zxAx4DzheYaNy643xaKrA== X-Received: by 2002:ae9:e20c:: with SMTP id c12mr49989037qkc.210.1563894166621; Tue, 23 Jul 2019 08:02:46 -0700 (PDT) Received: from redhat.com (bzq-79-181-91-42.red.bezeqint.net. [79.181.91.42]) by smtp.gmail.com with ESMTPSA id s25sm18898787qkm.130.2019.07.23.08.02.39 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Tue, 23 Jul 2019 08:02:45 -0700 (PDT) Date: Tue, 23 Jul 2019 11:02:37 -0400 From: "Michael S. Tsirkin" To: Jason Wang Subject: Re: WARNING in __mmdrop Message-ID: <20190723110219-mutt-send-email-mst@kernel.org> References: <20190721044615-mutt-send-email-mst@kernel.org> <75c43998-3a1c-676f-99ff-3d04663c3fcc@redhat.com> <20190722035657-mutt-send-email-mst@kernel.org> <20190723010156-mutt-send-email-mst@kernel.org> <124be1a2-1c53-8e65-0f06-ee2294710822@redhat.com> <20190723032800-mutt-send-email-mst@kernel.org> <20190723062221-mutt-send-email-mst@kernel.org> <9baa4214-67fd-7ad2-cbad-aadf90bbfc20@redhat.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <9baa4214-67fd-7ad2-cbad-aadf90bbfc20@redhat.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190723_080248_189688_24BB59E7 X-CRM114-Status: GOOD ( 19.03 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: mhocko@suse.com, peterz@infradead.org, ldv@altlinux.org, james.bottomley@hansenpartnership.com, linux-mm@kvack.org, namit@vmware.com, mingo@kernel.org, elena.reshetova@intel.com, keescook@chromium.org, aarcange@redhat.com, davem@davemloft.net, hch@infradead.org, christian@brauner.io, syzbot , syzkaller-bugs@googlegroups.com, jglisse@redhat.com, viro@zeniv.linux.org.uk, linux-arm-kernel@lists.infradead.org, wad@chromium.org, linux-parisc@vger.kernel.org, linux-kernel@vger.kernel.org, luto@amacapital.net, ebiederm@xmission.com, akpm@linux-foundation.org, guro@fb.com Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org T24gVHVlLCBKdWwgMjMsIDIwMTkgYXQgMDk6MzQ6MjlQTSArMDgwMCwgSmFzb24gV2FuZyB3cm90 ZToKPiAKPiBPbiAyMDE5LzcvMjMg5LiL5Y2INjoyNywgTWljaGFlbCBTLiBUc2lya2luIHdyb3Rl Ogo+ID4gPiBZZXMsIHNpbmNlIHRoZXJlIGNvdWxkIGJlIG11bHRpcGxlIGNvLWN1cnJlbnQgaW52 YWxpZGF0aW9uIHJlcXVlc3RzLiBXZSBuZWVkCj4gPiA+IGNvdW50IHRoZW0gdG8gbWFrZSBzdXJl IHdlIGRvbid0IHBpbiB3cm9uZyBwYWdlcy4KPiA+ID4gCj4gPiA+IAo+ID4gPiA+IEkgYWxzbyB3 b25kZXIgYWJvdXQgb3JkZXJpbmcuIGt2bSBoYXMgdGhpczoKPiA+ID4gPiAgICAgICAgICAvKgo+ ID4gPiA+ICAgICAgICAgICAgKiBVc2VkIHRvIGNoZWNrIGZvciBpbnZhbGlkYXRpb25zIGluIHBy b2dyZXNzLCBvZiB0aGUgcGZuIHRoYXQgaXMKPiA+ID4gPiAgICAgICAgICAgICogcmV0dXJuZWQg YnkgcGZuX3RvX3Bmbl9wcm90IGJlbG93Lgo+ID4gPiA+ICAgICAgICAgICAgKi8KPiA+ID4gPiAg ICAgICAgICAgbW11X3NlcSA9IGt2bS0+bW11X25vdGlmaWVyX3NlcTsKPiA+ID4gPiAgICAgICAg ICAgLyoKPiA+ID4gPiAgICAgICAgICAgICogRW5zdXJlIHRoZSByZWFkIG9mIG1tdV9ub3RpZmll cl9zZXEgaXNuJ3QgcmVvcmRlcmVkIHdpdGggUFRFIHJlYWRzIGluCj4gPiA+ID4gICAgICAgICAg ICAqIGdmbl90b19wZm5fcHJvdCgpICh3aGljaCBjYWxscyBnZXRfdXNlcl9wYWdlcygpKSwgc28g dGhhdCB3ZSBkb24ndAo+ID4gPiA+ICAgICAgICAgICAgKiByaXNrIHRoZSBwYWdlIHdlIGdldCBh IHJlZmVyZW5jZSB0byBnZXR0aW5nIHVubWFwcGVkIGJlZm9yZSB3ZSBoYXZlIGEKPiA+ID4gPiAg ICAgICAgICAgICogY2hhbmNlIHRvIGdyYWIgdGhlIG1tdV9sb2NrIHdpdGhvdXQgbW11X25vdGlm aWVyX3JldHJ5KCkgbm90aWNpbmcuCj4gPiA+ID4gICAgICAgICAgICAqCj4gPiA+ID4gICAgICAg ICAgICAqIFRoaXMgc21wX3JtYigpIHBhaXJzIHdpdGggdGhlIGVmZmVjdGl2ZSBzbXBfd21iKCkg b2YgdGhlIGNvbWJpbmF0aW9uCj4gPiA+ID4gICAgICAgICAgICAqIG9mIHRoZSBwdGVfdW5tYXBf dW5sb2NrKCkgYWZ0ZXIgdGhlIFBURSBpcyB6YXBwZWQsIGFuZCB0aGUKPiA+ID4gPiAgICAgICAg ICAgICogc3Bpbl9sb2NrKCkgaW4ga3ZtX21tdV9ub3RpZmllcl9pbnZhbGlkYXRlXzxwYWdlfHJh bmdlX2VuZD4oKSBiZWZvcmUKPiA+ID4gPiAgICAgICAgICAgICogbW11X25vdGlmaWVyX3NlcSBp cyBpbmNyZW1lbnRlZC4KPiA+ID4gPiAgICAgICAgICAgICovCj4gPiA+ID4gICAgICAgICAgIHNt cF9ybWIoKTsKPiA+ID4gPiAKPiA+ID4gPiBkb2VzIHRoaXMgYXBwbHkgdG8gdXM/IENhbid0IHdl IHVzZSBhIHNlcWxvY2sgaW5zdGVhZCBzbyB3ZSBkbwo+ID4gPiA+IG5vdCBuZWVkIHRvIHdvcnJ5 Pwo+ID4gPiBJJ20gbm90IGZhbWlsaWFyIHdpdGgga3ZtIE1NVSBpbnRlcm5hbHMsIGJ1dCB3ZSBk byBldmVyeXRoaW5nIHVuZGVyIG9mCj4gPiA+IG1tdV9sb2NrLgo+ID4gPiAKPiA+ID4gVGhhbmtz Cj4gPiBJIGRvbid0IHRoaW5rIHRoaXMgaGVscHMgYXQgYWxsLgo+ID4gCj4gPiBUaGVyZSdzIG5v IGxvY2sgYmV0d2VlbiBjaGVja2luZyB0aGUgaW52YWxpZGF0ZSBjb3VudGVyIGFuZAo+ID4gZ2V0 IHVzZXIgcGFnZXMgZmFzdCB3aXRoaW4gdmhvc3RfbWFwX3ByZWZldGNoLiBTbyBpdCdzIHBvc3Np YmxlCj4gPiB0aGF0IGdldCB1c2VyIHBhZ2VzIGZhc3QgcmVhZHMgUFRFcyBzcGVjdWxhdGl2ZWx5 IGJlZm9yZQo+ID4gaW52YWxpZGF0ZSBpcyByZWFkLgo+ID4gCj4gPiAtLSAKPiAKPiAKPiBJbiB2 aG9zdF9tYXBfcHJlZmV0Y2goKSB3ZSBkbzoKPiAKPiDCoMKgwqDCoMKgwqDCoCBzcGluX2xvY2so JnZxLT5tbXVfbG9jayk7Cj4gCj4gwqAgwqAgwqAgwqAgLi4uCj4gCj4gwqDCoMKgwqDCoMKgwqAg ZXJyID0gLUVGQVVMVDsKPiDCoMKgwqDCoMKgwqDCoCBpZiAodnEtPmludmFsaWRhdGVfY291bnQp Cj4gwqDCoMKgwqDCoMKgwqDCoMKgwqDCoMKgwqDCoMKgIGdvdG8gZXJyOwo+IAo+IMKgwqDCoMKg wqDCoMKgIC4uLgo+IAo+IMKgwqDCoMKgwqDCoMKgIG5waW5uZWQgPSBfX2dldF91c2VyX3BhZ2Vz X2Zhc3QodWFkZHItPnVhZGRyLCBucGFnZXMsCj4gwqDCoMKgwqDCoMKgwqDCoMKgwqDCoMKgwqDC oMKgwqDCoMKgwqDCoMKgwqDCoMKgwqDCoMKgwqDCoMKgwqDCoMKgwqDCoMKgwqDCoMKgIHVhZGRy LT53cml0ZSwgcGFnZXMpOwo+IAo+IMKgwqDCoMKgwqDCoMKgIC4uLgo+IAo+IMKgwqDCoCDCoMKg wqAgc3Bpbl91bmxvY2soJnZxLT5tbXVfbG9jayk7Cj4gCj4gSXMgdGhpcyBub3Qgc3VmZmljaWVu dD8KPiAKPiBUaGFua3MKClNvIHdoYXQgb3JkZXJzIF9fZ2V0X3VzZXJfcGFnZXNfZmFzdCB3cnQg aW52YWxpZGF0ZV9jb3VudCByZWFkPwoKLS0gCk1TVAoKX19fX19fX19fX19fX19fX19fX19fX19f X19fX19fX19fX19fX19fX19fX19fX18KbGludXgtYXJtLWtlcm5lbCBtYWlsaW5nIGxpc3QKbGlu dXgtYXJtLWtlcm5lbEBsaXN0cy5pbmZyYWRlYWQub3JnCmh0dHA6Ly9saXN0cy5pbmZyYWRlYWQu b3JnL21haWxtYW4vbGlzdGluZm8vbGludXgtYXJtLWtlcm5lbAo=