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=-12.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 34C96C433B4 for ; Thu, 8 Apr 2021 06:35:07 +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 DB6686113B for ; Thu, 8 Apr 2021 06:35:06 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DB6686113B Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=suse.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.107058.204637 (Exim 4.92) (envelope-from ) id 1lUOFe-0003SU-9Y; Thu, 08 Apr 2021 06:34:50 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 107058.204637; Thu, 08 Apr 2021 06:34:50 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lUOFe-0003SN-6U; Thu, 08 Apr 2021 06:34:50 +0000 Received: by outflank-mailman (input) for mailman id 107058; Thu, 08 Apr 2021 06:34:48 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lUOFc-0003SI-Sz for xen-devel@lists.xenproject.org; Thu, 08 Apr 2021 06:34:48 +0000 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id 27c5cfa3-6d0e-44d5-aabd-c97cfeb1a925; Thu, 08 Apr 2021 06:34:47 +0000 (UTC) Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id E4795AFF0; Thu, 8 Apr 2021 06:34:46 +0000 (UTC) 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" X-Inumbo-ID: 27c5cfa3-6d0e-44d5-aabd-c97cfeb1a925 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1617863687; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=KoUIvLOfvNrykFIBuyDXFZG0FOvWgNiAZRFCjRfpXyg=; b=hWauGpSueEOD/RMbpRwBtSPYMR8VqcvWC+qNcygNBfOK9QMElqbtoQh9GPOMJz1SiqLE/p SdP39wqCeNkkwa+G1oXmVuvrlMbGPvnebQckX/ehU17nkvOQnT5apS0ORciemZTqXZeiDD sa4JiRXjHhnUEOVayAYmr/GGWxcSQNU= Subject: Re: [PATCH v3 06/11] x86/hvm: allowing registering EOI callbacks for GSIs To: =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= Cc: Andrew Cooper , Wei Liu , xen-devel@lists.xenproject.org References: <20210331103303.79705-1-roger.pau@citrix.com> <20210331103303.79705-7-roger.pau@citrix.com> From: Jan Beulich Message-ID: <06192f36-dae3-9626-3fe5-98722d2753f5@suse.com> Date: Thu, 8 Apr 2021 08:34:46 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.9.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit On 07.04.2021 19:08, Roger Pau Monné wrote: > On Wed, Apr 07, 2021 at 05:51:14PM +0200, Jan Beulich wrote: >> On 31.03.2021 12:32, Roger Pau Monne wrote: >>> +bool hvm_gsi_has_callbacks(const struct domain *d, unsigned int gsi) >>> +{ >>> + struct hvm_irq *hvm_irq = hvm_domain_irq(d); >>> + bool has_callbacks; >>> + >>> + read_lock(&hvm_irq->gsi_callbacks_lock); >>> + has_callbacks = !list_empty(&hvm_irq->gsi_callbacks[gsi]); >>> + read_unlock(&hvm_irq->gsi_callbacks_lock); >>> + >>> + return has_callbacks; >>> +} >> >> What use is this function? Its result is stale by the time the >> caller can look at it, as you've dropped the lock. > > Right, that function is only used to decide whether the vIOAPIC needs > to register an EOI callback when injecting a vector to the vlapic. The > workflow is to first register a callback with the vIOAPIC and > afterwards inject an interrupt which will trigger the callback > logic. > > Playing with the callback registration while interrupts can be > injected will likely result in a malfunction of the device that relies > on those callbacks, but that's to be expected anyway when playing such > games. > > That said multiple users sharing a vIOAPIC pin should be fine as long > as they follow the logic above: always register a callback before > attempting to inject an interrupt. May I ask that you add a comment ahead of this function pointing out the restriction? >>> @@ -443,7 +457,8 @@ static void ioapic_inj_irq( >>> struct vlapic *target, >>> uint8_t vector, >>> uint8_t trig_mode, >>> - uint8_t delivery_mode) >>> + uint8_t delivery_mode, >>> + bool callback) >>> { >>> HVM_DBG_LOG(DBG_LEVEL_IOAPIC, "irq %d trig %d deliv %d", >>> vector, trig_mode, delivery_mode); >>> @@ -452,7 +467,7 @@ static void ioapic_inj_irq( >>> (delivery_mode == dest_LowestPrio)); >>> >>> vlapic_set_irq_callback(target, vector, trig_mode, >>> - trig_mode ? eoi_callback : NULL, NULL); >>> + callback ? eoi_callback : NULL, NULL); >> >> I think you'd better use trig_mode || callback here and ... >> >>> @@ -466,6 +481,7 @@ static void vioapic_deliver(struct hvm_vioapic *vioapic, unsigned int pin) >>> struct vlapic *target; >>> struct vcpu *v; >>> unsigned int irq = vioapic->base_gsi + pin; >>> + bool callback = trig_mode || hvm_gsi_has_callbacks(d, irq); >>> >>> ASSERT(spin_is_locked(&d->arch.hvm.irq_lock)); >>> >>> @@ -492,7 +508,8 @@ static void vioapic_deliver(struct hvm_vioapic *vioapic, unsigned int pin) >>> target = vlapic_lowest_prio(d, NULL, 0, dest, dest_mode); >>> if ( target != NULL ) >>> { >>> - ioapic_inj_irq(vioapic, target, vector, trig_mode, delivery_mode); >>> + ioapic_inj_irq(vioapic, target, vector, trig_mode, delivery_mode, >>> + callback); >> >> ... invoke hvm_gsi_has_callbacks() right here and ... >> >>> @@ -507,7 +524,7 @@ static void vioapic_deliver(struct hvm_vioapic *vioapic, unsigned int pin) >>> for_each_vcpu ( d, v ) >>> if ( vlapic_match_dest(vcpu_vlapic(v), NULL, 0, dest, dest_mode) ) >>> ioapic_inj_irq(vioapic, vcpu_vlapic(v), vector, trig_mode, >>> - delivery_mode); >>> + delivery_mode, callback); >> >> ... here, avoiding to call the function when you don't need the >> result. > > I think there's a slim chance of not needing to use the callback local > variable, and hence didn't consider limiting it. I can do, but I'm > unsure this will bring any real benefit while making the code more > complex IMO. Really the variable remaining unused in a minor set of cases was only a secondary observation. What I first stumbled over is the moving of the decision whether a callback is wanted from ioapic_inj_irq() to its caller. Since the function clearly is intended as a helper of vioapic_deliver(), I guess in the end it's fine the way you have it. Jan