From patchwork Wed Nov 2 23:18:40 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sean Christopherson X-Patchwork-Id: 13029171 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 C2482C43217 for ; Wed, 2 Nov 2022 23:20:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230222AbiKBXUo (ORCPT ); Wed, 2 Nov 2022 19:20:44 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34080 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230376AbiKBXUN (ORCPT ); Wed, 2 Nov 2022 19:20:13 -0400 Received: from mail-yb1-xb4a.google.com (mail-yb1-xb4a.google.com [IPv6:2607:f8b0:4864:20::b4a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D47AF2DE6 for ; Wed, 2 Nov 2022 16:19:40 -0700 (PDT) Received: by mail-yb1-xb4a.google.com with SMTP id m200-20020a25d4d1000000b006cb7e26b93cso403857ybf.1 for ; Wed, 02 Nov 2022 16:19:40 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:reply-to:from:to:cc:subject:date:message-id:reply-to; bh=ny13H9j4cIjKO1SZwLLCS8PC9upQWvRm8VxGRZ8ZYmk=; b=aJLuaf2vXfUATM8W1/jE2OXBe4WAQ8dl1SISKNHYxZm6XYiaEQEldvLhewXR2eoETv Fw/jD0wjvKzFfk4tKXiMdcaQANZjBOqWFwpUTkCiYrS1KoWMoASaSZ1AAVRSXXWHKzcy J5winaqMDM1M55OWGJMjEIBCPn6rmyyWEn4JEc/So2d0X3wfww0UB3fpj4xWGWuHGH+o bs6a+b61s/pjW8I+hfWKEAZojN69i8ynJ5A/X5/CrkMV2FiIZWRTDzucxZRStyDIQPKv ZMaWAm5aAaOoUdh/mazRbnD+v8xZzK1hmty4pgDvHoXILXiliGAwX6BXN0kBESciCUz4 3jqg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:reply-to:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=ny13H9j4cIjKO1SZwLLCS8PC9upQWvRm8VxGRZ8ZYmk=; b=vtl2gJIzJfRZrPTKizD0xDs9847kMTZWt77KUtZIX2dtdOr9/l5w0Q4cOdrNhMXJex EYHHu9bIegx0XkUXRimeMG0hxNPvoFbl2c2YFFia0WNZvRSYR2/VN2ydeIngvO6n6cNX GfXbps7bBzsnmXgnV8fTF/gWaLBmSN2757ezxi+0lfArXuIQ/fyNVNrB6lEn0D+5R5z8 M8LndrqLaLOALKugOiTBBIRH1LPxIBK3UxYjC84gttMIXhWuwwChQH5N6rKrnkRkxr0J Q+tjbk38h7lObDe2vS4o02xtKtBu55YHglzSYIEBZ/En5wN53eBKfJ1bDWKfOrYC+7sQ Be5Q== X-Gm-Message-State: ACrzQf38cglk3BCDyNQ3FvvoymeoYzfQw+FEgklfcRh1U/QfuPp29D3u 4G6ebPJd3k/7Rzx1RDLDBY+VuIxHQGU= X-Google-Smtp-Source: AMsMyM4ziWAoxK3B7TTCH6W4aFyoFb3DGw1decUo8flpRCJHJwk9oxmuretGO0t2fbQiTdSn9tHNgCtS0bI= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a05:6902:703:b0:6ca:a928:159f with SMTP id k3-20020a056902070300b006caa928159fmr25507895ybt.303.1667431176012; Wed, 02 Nov 2022 16:19:36 -0700 (PDT) Reply-To: Sean Christopherson Date: Wed, 2 Nov 2022 23:18:40 +0000 In-Reply-To: <20221102231911.3107438-1-seanjc@google.com> Mime-Version: 1.0 References: <20221102231911.3107438-1-seanjc@google.com> X-Mailer: git-send-email 2.38.1.431.g37b22c650d-goog Message-ID: <20221102231911.3107438-14-seanjc@google.com> Subject: [PATCH 13/44] KVM: x86: Serialize vendor module initialization (hardware setup) From: Sean Christopherson To: Paolo Bonzini , Marc Zyngier , Huacai Chen , Aleksandar Markovic , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Christian Borntraeger , Janosch Frank , Claudio Imbrenda , Matthew Rosato , Eric Farman , Sean Christopherson , Vitaly Kuznetsov Cc: James Morse , Alexandru Elisei , Suzuki K Poulose , Oliver Upton , Atish Patra , David Hildenbrand , kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, kvmarm@lists.cs.columbia.edu, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, Isaku Yamahata , Fabiano Rosas , Michael Ellerman , Chao Gao , Thomas Gleixner , Yuan Yao Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org Acquire a new mutex, vendor_module_lock, in kvm_x86_vendor_init() while doing hardware setup to ensure that concurrent calls are fully serialized. KVM rejects attempts to load vendor modules if a different module has already been loaded, but doesn't handle the case where multiple vendor modules are loaded at the same time, and module_init() doesn't run under the global module_mutex. Note, in practice, this is likely a benign bug as no platform exists that supports both SVM and VMX, i.e. barring a weird VM setup, one of the vendor modules is guaranteed to fail a support check before modifying common KVM state. Alternatively, KVM could perform an atomic CMPXCHG on .hardware_enable, but that comes with its own ugliness as it would require setting .hardware_enable before success is guaranteed, e.g. attempting to load the "wrong" could result in spurious failure to load the "right" module. Introduce a new mutex as using kvm_lock is extremely deadlock prone due to kvm_lock being taken under cpus_write_lock(), and in the future, under under cpus_read_lock(). Any operation that takes cpus_read_lock() while holding kvm_lock would potentially deadlock, e.g. kvm_timer_init() takes cpus_read_lock() to register a callback. In theory, KVM could avoid such problematic paths, i.e. do less setup under kvm_lock, but avoiding all calls to cpus_read_lock() is subtly difficult and thus fragile. E.g. updating static calls also acquires cpus_read_lock(). Inverting the lock ordering, i.e. always taking kvm_lock outside cpus_read_lock(), is not a viable option, e.g. kvm_online_cpu() takes kvm_lock and is called under cpus_write_lock(). The lockdep splat below is dependent on future patches to take cpus_read_lock() in hardware_enable_all(), but as above, deadlock is already is already possible. ====================================================== WARNING: possible circular locking dependency detected 6.0.0-smp--7ec93244f194-init2 #27 Tainted: G O ------------------------------------------------------ stable/251833 is trying to acquire lock: ffffffffc097ea28 (kvm_lock){+.+.}-{3:3}, at: hardware_enable_all+0x1f/0xc0 [kvm] but task is already holding lock: ffffffffa2456828 (cpu_hotplug_lock){++++}-{0:0}, at: hardware_enable_all+0xf/0xc0 [kvm] which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (cpu_hotplug_lock){++++}-{0:0}: cpus_read_lock+0x2a/0xa0 __cpuhp_setup_state+0x2b/0x60 __kvm_x86_vendor_init+0x16a/0x1870 [kvm] kvm_x86_vendor_init+0x23/0x40 [kvm] 0xffffffffc0a4d02b do_one_initcall+0x110/0x200 do_init_module+0x4f/0x250 load_module+0x1730/0x18f0 __se_sys_finit_module+0xca/0x100 __x64_sys_finit_module+0x1d/0x20 do_syscall_64+0x3d/0x80 entry_SYSCALL_64_after_hwframe+0x63/0xcd -> #0 (kvm_lock){+.+.}-{3:3}: __lock_acquire+0x16f4/0x30d0 lock_acquire+0xb2/0x190 __mutex_lock+0x98/0x6f0 mutex_lock_nested+0x1b/0x20 hardware_enable_all+0x1f/0xc0 [kvm] kvm_dev_ioctl+0x45e/0x930 [kvm] __se_sys_ioctl+0x77/0xc0 __x64_sys_ioctl+0x1d/0x20 do_syscall_64+0x3d/0x80 entry_SYSCALL_64_after_hwframe+0x63/0xcd other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(cpu_hotplug_lock); lock(kvm_lock); lock(cpu_hotplug_lock); lock(kvm_lock); *** DEADLOCK *** 1 lock held by stable/251833: #0: ffffffffa2456828 (cpu_hotplug_lock){++++}-{0:0}, at: hardware_enable_all+0xf/0xc0 [kvm] Signed-off-by: Sean Christopherson --- arch/x86/kvm/x86.c | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index a0ca401d3cdf..218707597bea 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -128,6 +128,7 @@ static int kvm_vcpu_do_singlestep(struct kvm_vcpu *vcpu); static int __set_sregs2(struct kvm_vcpu *vcpu, struct kvm_sregs2 *sregs2); static void __get_sregs2(struct kvm_vcpu *vcpu, struct kvm_sregs2 *sregs2); +static DEFINE_MUTEX(vendor_module_lock); struct kvm_x86_ops kvm_x86_ops __read_mostly; #define KVM_X86_OP(func) \ @@ -9280,7 +9281,7 @@ void kvm_arch_exit(void) } -int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops) +static int __kvm_x86_vendor_init(struct kvm_x86_init_ops *ops) { u64 host_pat; int r; @@ -9413,6 +9414,17 @@ int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops) kmem_cache_destroy(x86_emulator_cache); return r; } + +int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops) +{ + int r; + + mutex_lock(&vendor_module_lock); + r = __kvm_x86_vendor_init(ops); + mutex_unlock(&vendor_module_lock); + + return r; +} EXPORT_SYMBOL_GPL(kvm_x86_vendor_init); void kvm_x86_vendor_exit(void) @@ -9435,7 +9447,6 @@ void kvm_x86_vendor_exit(void) cancel_work_sync(&pvclock_gtod_work); #endif static_call(kvm_x86_hardware_unsetup)(); - kvm_x86_ops.hardware_enable = NULL; kvm_mmu_vendor_module_exit(); free_percpu(user_return_msrs); kmem_cache_destroy(x86_emulator_cache); @@ -9443,6 +9454,9 @@ void kvm_x86_vendor_exit(void) static_key_deferred_flush(&kvm_xen_enabled); WARN_ON(static_branch_unlikely(&kvm_xen_enabled.key)); #endif + mutex_lock(&vendor_module_lock); + kvm_x86_ops.hardware_enable = NULL; + mutex_unlock(&vendor_module_lock); } EXPORT_SYMBOL_GPL(kvm_x86_vendor_exit);