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 84D11C433FE for ; Wed, 16 Nov 2022 03:09:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231869AbiKPDJC (ORCPT ); Tue, 15 Nov 2022 22:09:02 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36750 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230244AbiKPDI4 (ORCPT ); Tue, 15 Nov 2022 22:08:56 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4F87D10056; Tue, 15 Nov 2022 19:08:55 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id EC941B818E0; Wed, 16 Nov 2022 03:08:53 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8F2B1C433D6; Wed, 16 Nov 2022 03:08:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1668568132; bh=Zd6O46v+aOYouGnAna4jIIJwIb+cPMsXGDMUfy7dDc0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=n8zFaBT8FSrppdZnfPmFvvxlCBHBydmyVNfoo/OChYwOrnOBkjltj3DTJWd363Tv1 WSOhxfcntqPbc/cHA5UJfqPkm9SkDKTxgFDEZ0sLGP4alGnEcmCjNzcJhY8VdVxMSG nd8wk6qhWl141iiJhkM3b5NJaFHrONNKYP//Wc2Qa3AhytabEUseOUWS+Wo78pmkSx qB6f/F/eP0qziMdvYyDd4mPJ9rxVGM9zRt4ZSU0K5T1l2dJx/0m40HNs9oyxiHbaqN SMniSji+W31VO0hskljfBfWd2m74AzVOnZ7BmpAgj3fGdNwgyV9bOsuTLXAbaMQOnt celo2gvZygaLQ== Received: from sofa.misterjones.org ([185.219.108.64] helo=goblin-girl.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.95) (envelope-from ) id 1ov8nC-006Lpn-4m; Wed, 16 Nov 2022 03:08:50 +0000 Date: Wed, 16 Nov 2022 03:08:49 +0000 Message-ID: <868rkbppdq.wl-maz@kernel.org> From: Marc Zyngier To: Oliver Upton Cc: James Morse , Alexandru Elisei , Suzuki K Poulose , Catalin Marinas , Will Deacon , linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, kvmarm@lists.linux.dev, Marek Szyprowski , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] KVM: arm64: Don't acquire RCU read lock for exclusive table walks In-Reply-To: <20221115225502.2240227-1-oliver.upton@linux.dev> References: <20221115225502.2240227-1-oliver.upton@linux.dev> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: oliver.upton@linux.dev, james.morse@arm.com, alexandru.elisei@arm.com, suzuki.poulose@arm.com, catalin.marinas@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, kvmarm@lists.linux.dev, m.szyprowski@samsung.com, linux-kernel@vger.kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 15 Nov 2022 22:55:02 +0000, Oliver Upton wrote: > > Marek reported a BUG resulting from the recent parallel faults changes, > as the hyp stage-1 map walker attempted to allocate table memory while > holding the RCU read lock: > > BUG: sleeping function called from invalid context at > include/linux/sched/mm.h:274 > in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid: 1, name: swapper/0 > preempt_count: 0, expected: 0 > RCU nest depth: 1, expected: 0 > 2 locks held by swapper/0/1: > #0: ffff80000a8a44d0 (kvm_hyp_pgd_mutex){+.+.}-{3:3}, at: > __create_hyp_mappings+0x80/0xc4 > #1: ffff80000a927720 (rcu_read_lock){....}-{1:2}, at: > kvm_pgtable_walk+0x0/0x1f4 > CPU: 2 PID: 1 Comm: swapper/0 Not tainted 6.1.0-rc3+ #5918 > Hardware name: Raspberry Pi 3 Model B (DT) > Call trace: > dump_backtrace.part.0+0xe4/0xf0 > show_stack+0x18/0x40 > dump_stack_lvl+0x8c/0xb8 > dump_stack+0x18/0x34 > __might_resched+0x178/0x220 > __might_sleep+0x48/0xa0 > prepare_alloc_pages+0x178/0x1a0 > __alloc_pages+0x9c/0x109c > alloc_page_interleave+0x1c/0xc4 > alloc_pages+0xec/0x160 > get_zeroed_page+0x1c/0x44 > kvm_hyp_zalloc_page+0x14/0x20 > hyp_map_walker+0xd4/0x134 > kvm_pgtable_visitor_cb.isra.0+0x38/0x5c > __kvm_pgtable_walk+0x1a4/0x220 > kvm_pgtable_walk+0x104/0x1f4 > kvm_pgtable_hyp_map+0x80/0xc4 > __create_hyp_mappings+0x9c/0xc4 > kvm_mmu_init+0x144/0x1cc > kvm_arch_init+0xe4/0xef4 > kvm_init+0x3c/0x3d0 > arm_init+0x20/0x30 > do_one_initcall+0x74/0x400 > kernel_init_freeable+0x2e0/0x350 > kernel_init+0x24/0x130 > ret_from_fork+0x10/0x20 > > Since the hyp stage-1 table walkers are serialized by kvm_hyp_pgd_mutex, > RCU protection really doesn't add anything. Don't acquire the RCU read > lock for an exclusive walk. While at it, add a warning which codifies > the lack of support for shared walks in the hypervisor code. > > Reported-by: Marek Szyprowski > Signed-off-by: Oliver Upton > --- > > Applies on top of the parallel faults series that was picked up last > week. Tested with kvm-arm.mode={nvhe,protected} on an Ampere Altra > system. > > v1 -> v2: > - Took Will's suggestion of conditioning RCU on a flag, small tweak to > use existing bit instead (Thanks!) > > arch/arm64/include/asm/kvm_pgtable.h | 22 ++++++++++++++++------ > arch/arm64/kvm/hyp/pgtable.c | 5 +++-- > 2 files changed, 19 insertions(+), 8 deletions(-) > > diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h > index a874ce0ce7b5..d4c7321fa652 100644 > --- a/arch/arm64/include/asm/kvm_pgtable.h > +++ b/arch/arm64/include/asm/kvm_pgtable.h > @@ -51,8 +51,16 @@ static inline kvm_pte_t *kvm_dereference_pteref(kvm_pteref_t pteref, bool shared > return pteref; > } > > -static inline void kvm_pgtable_walk_begin(void) {} > -static inline void kvm_pgtable_walk_end(void) {} > +static inline void kvm_pgtable_walk_begin(bool shared) > +{ > + /* > + * Due to the lack of RCU (or a similar protection scheme), only > + * non-shared table walkers are allowed in the hypervisor. > + */ > + WARN_ON(shared); > +} > + > +static inline void kvm_pgtable_walk_end(bool shared) {} > > static inline bool kvm_pgtable_walk_lock_held(void) > { > @@ -68,14 +76,16 @@ static inline kvm_pte_t *kvm_dereference_pteref(kvm_pteref_t pteref, bool shared > return rcu_dereference_check(pteref, !shared); > } > > -static inline void kvm_pgtable_walk_begin(void) > +static inline void kvm_pgtable_walk_begin(bool shared) I'm not crazy about this sort of parameters. I think it would make a lot more sense to pass a pointer to the walker structure and do the flag check inside the helper. That way, we avoid extra churn if/when we need extra state or bookkeeping around the walk. Thanks, M. -- Without deviation from the norm, progress is not possible.