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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 00723C433F5 for ; Wed, 19 Jan 2022 19:22:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239741AbiASTW1 (ORCPT ); Wed, 19 Jan 2022 14:22:27 -0500 Received: from foss.arm.com ([217.140.110.172]:35976 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237071AbiASTW0 (ORCPT ); Wed, 19 Jan 2022 14:22:26 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 514811FB; Wed, 19 Jan 2022 11:22:25 -0800 (PST) Received: from C02TD0UTHF1T.local (unknown [10.57.36.53]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id CF5673F73D; Wed, 19 Jan 2022 11:22:19 -0800 (PST) Date: Wed, 19 Jan 2022 19:22:17 +0000 From: Mark Rutland To: Christian Borntraeger Cc: linux-kernel@vger.kernel.org, Paolo Bonzini , Michael Ellerman , aleksandar.qemu.devel@gmail.com, alexandru.elisei@arm.com, anup.patel@wdc.com, aou@eecs.berkeley.edu, atish.patra@wdc.com, bp@alien8.de, catalin.marinas@arm.com, chenhuacai@kernel.org, dave.hansen@linux.intel.com, frankja@linux.ibm.com, frederic@kernel.org, gor@linux.ibm.com, hca@linux.ibm.com, james.morse@arm.com, jmattson@google.com, joro@8bytes.org, luto@kernel.org, maz@kernel.org, mingo@redhat.com, nsaenzju@redhat.com, palmer@dabbelt.com, paulmck@kernel.org, paul.walmsley@sifive.com, peterz@infradead.org, seanjc@google.com, suzuki.poulose@arm.com, svens@linux.ibm.com, tglx@linutronix.de, tsbogend@alpha.franken.de, vkuznets@redhat.com, wanpengli@tencent.com, will@kernel.org, Anup Patel , Atish Patra Subject: Re: [PATCH v2 0/7] kvm: fix latent guest entry/exit bugs Message-ID: <20220119192217.GD43919@C02TD0UTHF1T.local> References: <20220119105854.3160683-1-mark.rutland@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 19, 2022 at 07:25:20PM +0100, Christian Borntraeger wrote: > Am 19.01.22 um 11:58 schrieb Mark Rutland: > > > CCing new emails for Anup and Atish so that they are aware of this thread. Ah; whoops. I'd meant to fix the Ccs on the patches. Thanks! [...] > I just gave this a spin on s390 with debugging on and I got the following: > > [ 457.151295] ------------[ cut here ]------------ > [ 457.151311] WARNING: CPU: 14 PID: 0 at kernel/rcu/tree.c:613 rcu_eqs_enter.constprop.0+0xf8/0x118 Hmm, so IIUC that's: WARN_ON_ONCE(rdp->dynticks_nmi_nesting != DYNTICK_IRQ_NONIDLE); ... and we're clearly in the idle thread here. I wonder, is the s390 guest entry/exit *preemptible* ? If a timer IRQ can preempt in the middle of the EQS, we wouldn't balance things before a ctx-switch to the idle thread, which would then be able to hit this. I'll need to go audit the other architectures for similar. Thanks, Mark. > [ 457.151324] Modules linked in: vhost_vsock vmw_vsock_virtio_transport_common vsock vhost vhost_iotlb xt_CHECKSUM xt_MASQUERADE xt_conntrack ipt_REJECT xt_tcpudp nft_compat nf_nat_tftp nft_objref nf_conntrack_tftp nft_counter kvm nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct nft_chain_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 ip_set nf_tables nfnetlink sunrpc mlx5_ib ib_uverbs s390_trng ib_core genwqe_card crc_itu_t vfio_ccw mdev vfio_iommu_type1 eadm_sch vfio zcrypt_cex4 sch_fq_codel configfs ip_tables x_tables mlx5_core ghash_s390 prng aes_s390 des_s390 libdes sha3_512_s390 sha3_256_s390 sha512_s390 sha256_s390 sha1_s390 sha_common pkey zcrypt rng_core autofs4 > [ 457.151422] CPU: 14 PID: 0 Comm: swapper/14 Not tainted 5.16.0-00007-g89e9021389e2 #3 > [ 457.151428] Hardware name: IBM 3906 M04 704 (LPAR) > [ 457.151432] Krnl PSW : 0404d00180000000 00000000a7c0495c (rcu_eqs_enter.constprop.0+0xfc/0x118) > [ 457.151440] R:0 T:1 IO:0 EX:0 Key:0 M:1 W:0 P:0 AS:3 CC:1 PM:0 RI:0 EA:3 > [ 457.151445] Krnl GPRS: ffffffffebd81d31 4000000000000000 0000000000000070 00000000a7fd7024 > [ 457.151450] 0000000000000000 0000000000000001 0000000000000000 0000000000000000 > [ 457.151454] 000000000000000e 000000000000000e 00000000a84d3a88 0000001fd8645c00 > [ 457.151458] 0000000000000000 0000000000000000 00000000a7c04882 0000038000653dc0 > [ 457.151468] Krnl Code: 00000000a7c0494c: ebaff0a00004 lmg %r10,%r15,160(%r15) > 00000000a7c04952: c0f4fffffef7 brcl 15,00000000a7c04740 > #00000000a7c04958: af000000 mc 0,0 > >00000000a7c0495c: a7f4ffa3 brc 15,00000000a7c048a2 > 00000000a7c04960: c0e500003f70 brasl %r14,00000000a7c0c840 > 00000000a7c04966: a7f4ffcd brc 15,00000000a7c04900 > 00000000a7c0496a: c0e500003f6b brasl %r14,00000000a7c0c840 > 00000000a7c04970: a7f4ffde brc 15,00000000a7c0492c > [ 457.151527] Call Trace: > [ 457.151530] [<00000000a7c0495c>] rcu_eqs_enter.constprop.0+0xfc/0x118 > [ 457.151536] ([<00000000a7c04882>] rcu_eqs_enter.constprop.0+0x22/0x118) > [ 457.151540] [<00000000a7c14cd2>] default_idle_call+0x62/0xd8 > [ 457.151545] [<00000000a6f816c6>] do_idle+0xf6/0x1b0 > [ 457.151553] [<00000000a6f81a06>] cpu_startup_entry+0x36/0x40 > [ 457.151558] [<00000000a7c16abe>] restart_int_handler+0x6e/0x90 > [ 457.151563] no locks held by swapper/14/0. > [ 457.151567] Last Breaking-Event-Address: > [ 457.151570] [<00000000a7c0489e>] rcu_eqs_enter.constprop.0+0x3e/0x118 > [ 457.151574] irq event stamp: 608654 > [ 457.151578] hardirqs last enabled at (608653): [<00000000a70190d8>] tick_nohz_idle_enter+0xb0/0x130 > [ 457.151584] hardirqs last disabled at (608654): [<00000000a6f8173e>] do_idle+0x16e/0x1b0 > [ 457.151589] softirqs last enabled at (608586): [<00000000a7c1861a>] __do_softirq+0x4ba/0x668 > [ 457.151594] softirqs last disabled at (608581): [<00000000a6f367c6>] __irq_exit_rcu+0x13e/0x170 > [ 457.151600] ---[ end trace 2ae2154f9724de86 ]--- > > I can not see right now whats wrong, your patches look sane.