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=-7.1 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,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 62522C433DF for ; Thu, 23 Jul 2020 06:24:57 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (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 11241206C1 for ; Thu, 23 Jul 2020 06:24:57 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=ozlabs.org header.i=@ozlabs.org header.b="STIApXPn" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 11241206C1 Authentication-Results: mail.kernel.org; dmarc=pass (p=none dis=none) header.from=ozlabs.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 4BC2PL3tGZzDr1f for ; Thu, 23 Jul 2020 16:24:54 +1000 (AEST) Received: from ozlabs.org (bilbo.ozlabs.org [203.11.71.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4BC2KB5Km2zDq94 for ; Thu, 23 Jul 2020 16:21:18 +1000 (AEST) Authentication-Results: lists.ozlabs.org; dmarc=pass (p=none dis=none) header.from=ozlabs.org Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; secure) header.d=ozlabs.org header.i=@ozlabs.org header.a=rsa-sha256 header.s=201707 header.b=STIApXPn; dkim-atps=neutral Received: by ozlabs.org (Postfix, from userid 1003) id 4BC2KB2xDyz9sRk; Thu, 23 Jul 2020 16:21:18 +1000 (AEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ozlabs.org; s=201707; t=1595485278; bh=Hng+7vJtSFdsdAyaoYogZg96Z3E9Fp8ldUBgLr4JUIg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=STIApXPneoXxhoQFSZ5MpmTejJzmzvfiGr7sM25Fw/5Ah0M8s79IeWSWT50pKiez2 T+j+LtWnMeW1BQ6qgMw/KEcAjJXnLsA9cIBjJhbF/BL06+nGKNDSJcCNUhdu/8vgIW 41TYg/WTi7/xYRdmwjDuIQHjIRqzAlE8lApfCbAoHFUdoOBvYlBbf0b4cov2oMrVAf 08ukd8vtqfod2plDsam++HO/TSJUNYOGy/XPNguJtKXaKiTWsDphjC5+FrY3tqHF82 +fzwPE90goyF6i8sMym9vvD0llr/fbVTO4dHVY6UZAK2qawBQECDrmCTPzc15wK60B 2Y7KW4Sv+Fnrw== Date: Thu, 23 Jul 2020 16:19:42 +1000 From: Paul Mackerras To: Alexey Kardashevskiy Subject: Re: [PATCH kernel] KVM: PPC: Protect kvm_vcpu_read_guest with srcu locks Message-ID: <20200723061942.GD213782@thinks.paulus.ozlabs.org> References: <20200609021230.103494-1-aik@ozlabs.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200609021230.103494-1-aik@ozlabs.ru> X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linuxppc-dev@lists.ozlabs.org, kvm-ppc@vger.kernel.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Tue, Jun 09, 2020 at 12:12:29PM +1000, Alexey Kardashevskiy wrote: > The kvm_vcpu_read_guest/kvm_vcpu_write_guest used for nested guests > eventually call srcu_dereference_check to dereference a memslot and > lockdep produces a warning as neither kvm->slots_lock nor > kvm->srcu lock is held and kvm->users_count is above zero (>100 in fact). > > This wraps mentioned VCPU read/write helpers in srcu read lock/unlock as > it is done in other places. This uses vcpu->srcu_idx when possible. > > These helpers are only used for nested KVM so this may explain why > we did not see these before. > > Here is an example of a warning: > > ============================= > WARNING: suspicious RCU usage > 5.7.0-rc3-le_dma-bypass.3.2_a+fstn1 #897 Not tainted > ----------------------------- > include/linux/kvm_host.h:633 suspicious rcu_dereference_check() usage! > > other info that might help us debug this: > > rcu_scheduler_active = 2, debug_locks = 1 > 1 lock held by qemu-system-ppc/2752: > #0: c000200359016be0 (&vcpu->mutex){+.+.}-{3:3}, at: kvm_vcpu_ioctl+0x144/0xd80 [kvm] > > stack backtrace: > CPU: 80 PID: 2752 Comm: qemu-system-ppc Not tainted 5.7.0-rc3-le_dma-bypass.3.2_a+fstn1 #897 > Call Trace: > [c0002003591ab240] [c000000000b23ab4] dump_stack+0x190/0x25c (unreliable) > [c0002003591ab2b0] [c00000000023f954] lockdep_rcu_suspicious+0x140/0x164 > [c0002003591ab330] [c008000004a445f8] kvm_vcpu_gfn_to_memslot+0x4c0/0x510 [kvm] > [c0002003591ab3a0] [c008000004a44c18] kvm_vcpu_read_guest+0xa0/0x180 [kvm] > [c0002003591ab410] [c008000004ff9bd8] kvmhv_enter_nested_guest+0x90/0xb80 [kvm_hv] > [c0002003591ab980] [c008000004fe07bc] kvmppc_pseries_do_hcall+0x7b4/0x1c30 [kvm_hv] > [c0002003591aba10] [c008000004fe5d30] kvmppc_vcpu_run_hv+0x10a8/0x1a30 [kvm_hv] > [c0002003591abae0] [c008000004a5d954] kvmppc_vcpu_run+0x4c/0x70 [kvm] > [c0002003591abb10] [c008000004a56e54] kvm_arch_vcpu_ioctl_run+0x56c/0x7c0 [kvm] > [c0002003591abba0] [c008000004a3ddc4] kvm_vcpu_ioctl+0x4ac/0xd80 [kvm] > [c0002003591abd20] [c0000000006ebb58] ksys_ioctl+0x188/0x210 > [c0002003591abd70] [c0000000006ebc28] sys_ioctl+0x48/0xb0 > [c0002003591abdb0] [c000000000042764] system_call_exception+0x1d4/0x2e0 > [c0002003591abe20] [c00000000000cce8] system_call_common+0xe8/0x214 > > Signed-off-by: Alexey Kardashevskiy Thanks, patch applied to my kvm-ppc-next branch. Paul.