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=-7.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,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 8139DC4361B for ; Tue, 15 Dec 2020 07:28:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3490220791 for ; Tue, 15 Dec 2020 07:28:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726408AbgLOH2S (ORCPT ); Tue, 15 Dec 2020 02:28:18 -0500 Received: from mx2.suse.de ([195.135.220.15]:39676 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725816AbgLOH2S (ORCPT ); Tue, 15 Dec 2020 02:28:18 -0500 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=1608017251; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=nj9ihax1/LrptfS9HSC1+VTxcZq+NVNUTCtfqAvgkPo=; b=FozNUbfhAKc8ap0AvXU0MWeqHO0YYsbgxBpCqBLfwmZdg26YtFCRWG+CzdTZ+voDttAXG4 Cgea/51PqVE0bNbQ9w6SSKS327Oocp2np39zl9AApNdl+Ucec2sjKOJSyHImcnzP6+x9dw sPWSaMCky4j69xCMPosIrJmduYpkEec= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 59F13AC7F; Tue, 15 Dec 2020 07:27:31 +0000 (UTC) To: Julien Grall , aams@amazon.de Cc: linux-kernel@vger.kernel.org, "xen-devel@lists.xenproject.org" , foersleo@amazon.de References: From: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= Subject: Re: xen/evtchn: Interrupt for port 34, but apparently not enabled; per-user 00000000a86a4c1b on 5.10 Message-ID: Date: Tue, 15 Dec 2020 08:27:30 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 In-Reply-To: Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="aZ8yJ9HMcgUBjSDsb6zsumgc5RgbItXS0" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --aZ8yJ9HMcgUBjSDsb6zsumgc5RgbItXS0 Content-Type: multipart/mixed; boundary="ykQYKCMfBobgZ4ASufJVLpgcjHbZd6Ss7"; protected-headers="v1" From: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= To: Julien Grall , aams@amazon.de Cc: linux-kernel@vger.kernel.org, "xen-devel@lists.xenproject.org" , foersleo@amazon.de Message-ID: Subject: Re: xen/evtchn: Interrupt for port 34, but apparently not enabled; per-user 00000000a86a4c1b on 5.10 References: In-Reply-To: --ykQYKCMfBobgZ4ASufJVLpgcjHbZd6Ss7 Content-Type: multipart/mixed; boundary="------------BFD7A9977F6A02DCE726E85E" Content-Language: en-US This is a multi-part message in MIME format. --------------BFD7A9977F6A02DCE726E85E Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable On 14.12.20 22:25, Julien Grall wrote: > Hi Juergen, >=20 > When testing Linux 5.10 dom0, I could reliably hit the following warnin= g=20 > with using event 2L ABI: >=20 > [=C2=A0 589.591737] Interrupt for port 34, but apparently not enabled; = > per-user 00000000a86a4c1b > [=C2=A0 589.593259] WARNING: CPU: 0 PID: 1111 at=20 > /home/ANT.AMAZON.COM/jgrall/works/oss/linux/drivers/xen/evtchn.c:170=20 > evtchn_interrupt+0xeb/0x100 > [=C2=A0 589.595514] Modules linked in: > [=C2=A0 589.596145] CPU: 0 PID: 1111 Comm: qemu-system-i38 Tainted: G=20 > W=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 5.10.0+ #180 > [=C2=A0 589.597708] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009),= BIOS=20 > rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014 > [=C2=A0 589.599782] RIP: e030:evtchn_interrupt+0xeb/0x100 > [=C2=A0 589.600698] Code: 48 8d bb d8 01 00 00 ba 01 00 00 00 be 1d 00 = 00 00=20 > e8 d9 10 ca ff eb b2 8b 75 20 48 89 da 48 c7 c7 a8 31 3d 82 e8 65 29 a0= =20 > ff <0f> 0b e9 42 ff ff ff 0f 1f 40 00 66 2e 0f 1f 84 00 00 00 00 00 0f > [=C2=A0 589.604087] RSP: e02b:ffffc90040003e70 EFLAGS: 00010086 > [=C2=A0 589.605102] RAX: 0000000000000000 RBX: ffff888102091800 RCX:=20 > 0000000000000027 > [=C2=A0 589.606445] RDX: 0000000000000000 RSI: ffff88817fe19150 RDI:=20 > ffff88817fe19158 > [=C2=A0 589.607790] RBP: ffff88810f5ab980 R08: 0000000000000001 R09:=20 > 0000000000328980 > [=C2=A0 589.609134] R10: 0000000000000000 R11: ffffc90040003c70 R12:=20 > ffff888107fd3c00 > [=C2=A0 589.610484] R13: ffffc90040003ed4 R14: 0000000000000000 R15:=20 > ffff88810f5ffd80 > [=C2=A0 589.611828] FS:=C2=A0 00007f960c4b8ac0(0000) GS:ffff88817fe0000= 0(0000)=20 > knlGS:0000000000000000 > [=C2=A0 589.613348] CS:=C2=A0 10000e030 DS: 0000 ES: 0000 CR0: 00000000= 80050033 > [=C2=A0 589.614525] CR2: 00007f17ee72e000 CR3: 000000010f5b6000 CR4:=20 > 0000000000050660 > [=C2=A0 589.615874] Call Trace: > [=C2=A0 589.616402]=C2=A0 > [=C2=A0 589.616855]=C2=A0 __handle_irq_event_percpu+0x4e/0x2c0 > [=C2=A0 589.617784]=C2=A0 handle_irq_event_percpu+0x30/0x80 > [=C2=A0 589.618660]=C2=A0 handle_irq_event+0x3a/0x60 > [=C2=A0 589.619428]=C2=A0 handle_edge_irq+0x9b/0x1f0 > [=C2=A0 589.620209]=C2=A0 generic_handle_irq+0x4f/0x60 > [=C2=A0 589.621008]=C2=A0 evtchn_2l_handle_events+0x160/0x280 > [=C2=A0 589.621913]=C2=A0 __xen_evtchn_do_upcall+0x66/0xb0 > [=C2=A0 589.622767]=C2=A0 __xen_pv_evtchn_do_upcall+0x11/0x20 > [=C2=A0 589.623665]=C2=A0 asm_call_irq_on_stack+0x12/0x20 > [=C2=A0 589.624511]=C2=A0 > [=C2=A0 589.624978]=C2=A0 xen_pv_evtchn_do_upcall+0x77/0xf0 > [=C2=A0 589.625848]=C2=A0 exc_xen_hypervisor_callback+0x8/0x10 >=20 > This can be reproduced when creating/destroying guest in a loop.=20 > Although, I have struggled to reproduce it on a vanilla Xen. >=20 > After several hours of debugging, I think I have found the root cause. >=20 > While we only expect the unmask to happen when the event channel is=20 > EOIed, there is an unmask happening as part of handle_edge_irq() becaus= e=20 > the interrupt was seen as pending by another vCPU (IRQS_PENDING is set)= =2E >=20 > It turns out that the event channel is set for multiple vCPU is in=20 > cpu_evtchn_mask. This is happening because the affinity is not cleared = > when freeing an event channel. >=20 > The implementation of evtchn_2l_handle_events() will look for all the=20 > active interrupts for the current vCPU and later on clear the pending=20 > bit (via the ack() callback). IOW, I believe, this is not an atomic=20 > operation. >=20 > Even if Xen will notify the event to a single vCPU, evtchn_pending_sel = > may still be set on the other vCPU (thanks to a different event=20 > channel). Therefore, there is a chance that two vCPUs will try to handl= e=20 > the same interrupt. >=20 > The IRQ handler handle_edge_irq() is able to deal with that and will=20 > mask/unmask the interrupt. This will mess us with the lateeoi logic=20 > (although, I managed to reproduce it once without XSA-332). Thanks for the analysis! > My initial idea to fix the problem was to switch the affinity from CPU = X=20 > to CPU0 when the event channel is freed. >=20 > However, I am not sure this is enough because I haven't found anything = > yet preventing a race between evtchn_2l_handle_events9) and=20 > evtchn_2l_bind_vcpu(). >=20 > So maybe we want to introduce a refcounting (if there is nothing=20 > provided by the IRQ framework) and only unmask when the counter drop to= 0. >=20 > Any opinions? I think we don't need a refcount, but just the internal states "masked" and "eoi_pending" and unmask only if both are false. "masked" will be set when the event is being masked. When delivering a lateeoi irq "eoi_pending" will be set and "masked "reset. "masked" will be reset when a normal unmask is happening. And "eoi_pending" will be reset when a lateeoi is signaled. Any reset of "masked" and "eoi_pending" will check the other flag and do an unmask if both are false. I'll write a patch. 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