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[2620:137:e000::1:20]) by mx.google.com with ESMTP id nb4-20020a1709071c8400b007add6be8c86si12933419ejc.762.2022.11.15.15.04.26; Tue, 15 Nov 2022 15:05:03 -0800 (PST) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@linux.dev header.s=key1 header.b=i3gwY0qO; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=linux.dev Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231921AbiKOWzb (ORCPT + 99 others); Tue, 15 Nov 2022 17:55:31 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50376 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229797AbiKOWz2 (ORCPT ); Tue, 15 Nov 2022 17:55:28 -0500 Received: from out2.migadu.com (out2.migadu.com [188.165.223.204]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DF4652B274; Tue, 15 Nov 2022 14:55:25 -0800 (PST) X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1668552924; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=J7Rn9AcjldUeqhlwEDEwZXF5DiyqtkiLk+SNwNoYnn8=; b=i3gwY0qOHEiKLr/7Eozm9b/dwBtR5PMSaV0FLOuJDH80ckVgOWUSKYpqrg70BCkvDdaDeb 7Ttaim5m5itJ0tI9qE041GkR4+9U3LwrB3pamGnpIfSSVFKmmP1dUDNeLLdwiCHHtqKg2r gcx3XBAFZb7kCeJFkwkvI05chdIotwA= From: Oliver Upton To: Marc Zyngier , James Morse , Alexandru Elisei , Suzuki K Poulose , Oliver Upton , Catalin Marinas , Will Deacon Cc: 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: [PATCH v2] KVM: arm64: Don't acquire RCU read lock for exclusive table walks Date: Tue, 15 Nov 2022 22:55:02 +0000 Message-Id: <20221115225502.2240227-1-oliver.upton@linux.dev> MIME-Version: 1.0 X-Migadu-Flow: FLOW_OUT X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1749605158157134163?= X-GMAIL-MSGID: =?utf-8?q?1749605158157134163?= 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) { - rcu_read_lock(); + if (shared) + rcu_read_lock(); } -static inline void kvm_pgtable_walk_end(void) +static inline void kvm_pgtable_walk_end(bool shared) { - rcu_read_unlock(); + if (shared) + rcu_read_unlock(); } static inline bool kvm_pgtable_walk_lock_held(void) diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c index 5bca9610d040..16aed10e7e59 100644 --- a/arch/arm64/kvm/hyp/pgtable.c +++ b/arch/arm64/kvm/hyp/pgtable.c @@ -287,11 +287,12 @@ int kvm_pgtable_walk(struct kvm_pgtable *pgt, u64 addr, u64 size, .end = PAGE_ALIGN(walk_data.addr + size), .walker = walker, }; + bool shared = walker->flags & KVM_PGTABLE_WALK_SHARED; int r; - kvm_pgtable_walk_begin(); + kvm_pgtable_walk_begin(shared); r = _kvm_pgtable_walk(pgt, &walk_data); - kvm_pgtable_walk_end(); + kvm_pgtable_walk_end(shared); return r; }