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=-5.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,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 1107CC4727E for ; Wed, 30 Sep 2020 13:39:24 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (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 ADCEC206B7 for ; Wed, 30 Sep 2020 13:39:23 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="QpUHEc8F" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org ADCEC206B7 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from list by lists.xenproject.org with outflank-mailman.704.2355 (Exim 4.92) (envelope-from ) id 1kNcKA-0003Pi-KR; Wed, 30 Sep 2020 13:39:14 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 704.2355; Wed, 30 Sep 2020 13:39:14 +0000 X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1kNcKA-0003Pb-HD; Wed, 30 Sep 2020 13:39:14 +0000 Received: by outflank-mailman (input) for mailman id 704; Wed, 30 Sep 2020 13:39:13 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1kNcK8-0003PO-Uo for xen-devel@lists.xenproject.org; Wed, 30 Sep 2020 13:39:13 +0000 Received: from mail-lf1-x142.google.com (unknown [2a00:1450:4864:20::142]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id a7896829-2002-4ee4-822c-b1816c574fd3; Wed, 30 Sep 2020 13:39:12 +0000 (UTC) Received: by mail-lf1-x142.google.com with SMTP id y2so2175309lfy.10 for ; Wed, 30 Sep 2020 06:39:12 -0700 (PDT) Received: from [192.168.1.6] ([212.22.223.21]) by smtp.gmail.com with ESMTPSA id b7sm196832lfi.123.2020.09.30.06.39.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 30 Sep 2020 06:39:10 -0700 (PDT) Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1kNcK8-0003PO-Uo for xen-devel@lists.xenproject.org; Wed, 30 Sep 2020 13:39:13 +0000 X-Inumbo-ID: a7896829-2002-4ee4-822c-b1816c574fd3 Received: from mail-lf1-x142.google.com (unknown [2a00:1450:4864:20::142]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id a7896829-2002-4ee4-822c-b1816c574fd3; Wed, 30 Sep 2020 13:39:12 +0000 (UTC) Received: by mail-lf1-x142.google.com with SMTP id y2so2175309lfy.10 for ; Wed, 30 Sep 2020 06:39:12 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-transfer-encoding:content-language; bh=gYYiQVB5bAau0SLe67LyF0f3OKYgxH8Mgav77ILWZBA=; b=QpUHEc8FK3whsyID6ND5DdCe7Iw9+oXC1RM2OyRkVtdB1QzaXrt8CMGg6t17u7+7c+ FbnW1NX6DlJzVrKPZQgSzdLdXwJhKL/oVR8jpd34BGtXnfgf6fKG0Aok1FZ25wJPN5zg OudC4NAFv/K+Gxby+Smg362JqvzIoHBT/lqMZ8lQu9NAOhuVQq1GCTTMpOHFLZyu1fZy jFcvfTC9ZP5/jcYvi5KqPuwBxAZ4S7lZyScJ5coVFxVntlLop0MfpaRh6XZsHCUKH9gX lLiwy4a8816HeLUai03bVBs4fXFjBPYW7wFU82bUzwgKqGdawFg9UCXfmV+8KRSgTN2p 6zWA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-transfer-encoding :content-language; bh=gYYiQVB5bAau0SLe67LyF0f3OKYgxH8Mgav77ILWZBA=; b=blv8ddrwHEbcAVZNYpsDaOFBt9RddfyfBbIIoanDO75ydy78MgfPvB1Jf6os8venzR uGLnskvuIQxSQGRx/EMS/msDCQ26oDMg5pUKRcLzQhpISWkQ6JFcXDZJBEtqR9R4z05E C5CBNl5RyIoOGowD4KfbLJse7TiQDqjrQCqqn0FyUKLpEjCFOPXZPzuRDgx50b2ycFJi CpWgzSLd+ovG7ufeF3Ya7dU+HFHeZsKYmgt84Hw8vlIV/dS6TS84uVtWNkqGAwU9dhgc yz4lUPcCT1g0cwdvjTh2PVKvhsBsqK0RAw/8PBCdgPASEgDpytwFwiLSMbJSdd6q5vAM q51w== X-Gm-Message-State: AOAM530BVtPi2xAZLx+h3KTNGz56YOiuH/ynJRn6xs2FtsMt3GOEOgcH W3nVDy64TR/9RTOBTFxRmbQ= X-Google-Smtp-Source: ABdhPJzFwf4jfvbaUH4NVC+DFH1MxMC2Yz+APCzy+hGvG3MLQFLg5MDHLDebOrubtGs3bkP+Oz8YIA== X-Received: by 2002:ac2:4c19:: with SMTP id t25mr940139lfq.503.1601473150782; Wed, 30 Sep 2020 06:39:10 -0700 (PDT) Received: from [192.168.1.6] ([212.22.223.21]) by smtp.gmail.com with ESMTPSA id b7sm196832lfi.123.2020.09.30.06.39.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 30 Sep 2020 06:39:10 -0700 (PDT) Subject: Re: [PATCH V1 02/16] xen/ioreq: Make x86's IOREQ feature common To: 'Julien Grall' , xen-devel@lists.xenproject.org Cc: paul@xen.org, 'Oleksandr Tyshchenko' , 'Andrew Cooper' , 'George Dunlap' , 'Ian Jackson' , 'Jan Beulich' , 'Stefano Stabellini' , 'Wei Liu' , =?UTF-8?B?J1JvZ2VyIFBhdSBNb25uw6kn?= , 'Jun Nakajima' , 'Kevin Tian' , 'Tim Deegan' , 'Julien Grall' References: <1599769330-17656-1-git-send-email-olekstysh@gmail.com> <1599769330-17656-3-git-send-email-olekstysh@gmail.com> <3997a705-ccb1-4b8f-41ca-c5507360c759@xen.org> <000201d69314$97bd8fa0$c738aee0$@xen.org> From: Oleksandr Message-ID: Date: Wed, 30 Sep 2020 16:39:09 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <000201d69314$97bd8fa0$c738aee0$@xen.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Hi Julien On 25.09.20 11:19, Paul Durrant wrote: >> -----Original Message----- >> From: Julien Grall >> Sent: 24 September 2020 19:01 >> To: Oleksandr Tyshchenko ; xen-devel@lists.xenproject.org >> Cc: Oleksandr Tyshchenko ; Andrew Cooper ; >> George Dunlap ; Ian Jackson ; Jan Beulich >> ; Stefano Stabellini ; Wei Liu ; Roger Pau >> Monné ; Paul Durrant ; Jun Nakajima ; >> Kevin Tian ; Tim Deegan ; Julien Grall >> Subject: Re: [PATCH V1 02/16] xen/ioreq: Make x86's IOREQ feature common >> >> >> >> On 10/09/2020 21:21, Oleksandr Tyshchenko wrote: >>> +static bool hvm_wait_for_io(struct hvm_ioreq_vcpu *sv, ioreq_t *p) >>> +{ >>> + unsigned int prev_state = STATE_IOREQ_NONE; >>> + unsigned int state = p->state; >>> + uint64_t data = ~0; >>> + >>> + smp_rmb(); >>> + >>> + /* >>> + * The only reason we should see this condition be false is when an >>> + * emulator dying races with I/O being requested. >>> + */ >>> + while ( likely(state != STATE_IOREQ_NONE) ) >>> + { >>> + if ( unlikely(state < prev_state) ) >>> + { >>> + gdprintk(XENLOG_ERR, "Weird HVM ioreq state transition %u -> %u\n", >>> + prev_state, state); >>> + sv->pending = false; >>> + domain_crash(sv->vcpu->domain); >>> + return false; /* bail */ >>> + } >>> + >>> + switch ( prev_state = state ) >>> + { >>> + case STATE_IORESP_READY: /* IORESP_READY -> NONE */ >>> + p->state = STATE_IOREQ_NONE; >>> + data = p->data; >>> + break; >>> + >>> + case STATE_IOREQ_READY: /* IOREQ_{READY,INPROCESS} -> IORESP_READY */ >>> + case STATE_IOREQ_INPROCESS: >>> + wait_on_xen_event_channel(sv->ioreq_evtchn, >>> + ({ state = p->state; >>> + smp_rmb(); >>> + state != prev_state; })); >>> + continue; >> As I pointed out previously [1], this helper was implemented with the >> expectation that wait_on_xen_event_channel() will not return if the vCPU >> got rescheduled. >> >> However, this assumption doesn't hold on Arm. >> >> I can see two solution: >> 1) Re-execute the caller >> 2) Prevent an IOREQ to disappear until the loop finish. >> >> @Paul any opinions? > The ioreq control plane is largely predicated on there being no pending I/O when the state of a server is modified, and it is assumed that domain_pause() is sufficient to achieve this. If that assumption doesn't hold then we need additional synchronization. > > Paul > May I please clarify whether a concern still stands (with what was said above) and we need an additional synchronization on Arm? -- Regards, Oleksandr Tyshchenko