From patchwork Fri Aug 30 04:35:51 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sean Christopherson X-Patchwork-Id: 13784246 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id DAEACCA0EDF for ; Fri, 30 Aug 2024 04:37:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:Reply-To:List-Subscribe: List-Help:List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Type:Cc:To: From:Subject:Message-ID:References:Mime-Version:In-Reply-To:Date: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=aHFUvm+FsXoP3qIyVsbx5uEplmYhc4fKnKOy7PZyclA=; b=hmiAsc/tXKo87V7TX5By19WJhl CMoC8CyxlDxOvIGjAe0Zb+1z6KVlrtmZsMHuhQ19ccjbf8/a0S182t6wBZs3bBEDZ8WsVaMdKubsJ Mbo0IWTyFf5eRWjcIZpnyq5UdPcqvFPKA93Qqp/pTgTXqihV7VvtlZD+qUZWKBmnYzbTddubP5MyU o4SG2nSAFSF7nOs3QJpny3Chcuao7Z+ShAADfiVlPw5GXIdDbJ1le+W8ntRq7agRDAgL8vUMJabUZ DHqbzNzZFOtvYbvDbo25FCcQqi4HB/ZroP92RTijw7vNsvJq0xsD5PXYXcfJwa3ZBAJnAWuklw1C2 4q6kycvQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1sjtNy-00000004gDN-2cM6; Fri, 30 Aug 2024 04:37:22 +0000 Received: from mail-yw1-f202.google.com ([209.85.128.202]) by bombadil.infradead.org with esmtps (Exim 4.97.1 #2 (Red Hat Linux)) id 1sjtMm-00000004fk7-36tF for linux-arm-kernel@lists.infradead.org; Fri, 30 Aug 2024 04:36:11 +0000 Received: by mail-yw1-f202.google.com with SMTP id 00721157ae682-6d2c2cf7473so27065887b3.0 for ; Thu, 29 Aug 2024 21:36:07 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1724992566; x=1725597366; darn=lists.infradead.org; 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=aHFUvm+FsXoP3qIyVsbx5uEplmYhc4fKnKOy7PZyclA=; b=Qi+ds33ZuFhFL2WdIH3Oxf2Wcvsxt6b2pm+NZKZ0D3CbuF0vP577i23Cgepl/FlKLC tO/YeZG1cdwwUQOXZA7X+km905gkNJs5sF6tRFu/TGgvTdVm2CrCBtG5xcoLB/mWEUOT 1o4e8b0S9h3hWlU0Jhnsd31JK1g1ojtghUtuXJWwaEEDHEimOQxwZzrhJfZw7YNJm2zv LQGDXFZ3yaY/0G2NwECXSoE9dIyOHiuNPLgYGKceDglQMskazlMjdeJyOX2pbRL4fgWq KiUTLr3Y9TiseS7TN7s0hdtpqj5dmBXd38b13QiMf8g7YI8W+q+xjlrYmcXhfTsMBXBg Zx3g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1724992566; x=1725597366; 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=aHFUvm+FsXoP3qIyVsbx5uEplmYhc4fKnKOy7PZyclA=; b=P7GpxY1Thy58j0lBfvaD9MredGiP7vO1dDXlOPamg/w5uBnKIrNLyovca7tcu5fBBs eJ4/UyT4dTNCF4MN8zPBJsV5kwetNRm35ieu0AVqFLx4m1TxP74O1MwQBQxuijz7ty5L 3+ZJp3rXH+poMDhIRhFKQKPoINNNuAl2Ts6JuPBO4fF3jYKB/TCVonije0WJ4jblJ3fY ZWg5AHA8pUw4vRJe96hTdJ8wd7rc/PWyY9jcRBDP8O//BoltUk6ZCjR2nDQ1yt4XeiAU vo/Jw6tGbq90f1nSLhSn9JR0kZKq3RdU+SGKD0u6qAkAkNKagv05lV23jaiPEThVdAxg cSjw== X-Forwarded-Encrypted: i=1; AJvYcCUNwG5wQTtCYPYGKoZZGMOOYvKlc3V7dNXeYO8AtJK9yNX9U7+x5fbMwB9790dd95Psm2etWG/sXEogWcZl+UDU@lists.infradead.org X-Gm-Message-State: AOJu0YxNNuzx0eI2q+w+EJoZrzPT8ncR0w/jrx47qg0+V6I9x9ODga69 wpOcLftUWcDnsherK9CuiIZqopa6NuPT1/hwlXlQKGbT5Vrfs8++RUkGv1hWCotTZyyXmP1SJQ7 Hfw== X-Google-Smtp-Source: AGHT+IEEIm57E7ZhayVART8ADQcxGPIPqWcj0BvzrgRRlVCf3l6FJVWmFUT6VBh+RffSDLzBCOKmsEJxIDM= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a05:690c:63c8:b0:6af:623c:7694 with SMTP id 00721157ae682-6d40b0f96b2mr822357b3.0.1724992566315; Thu, 29 Aug 2024 21:36:06 -0700 (PDT) Date: Thu, 29 Aug 2024 21:35:51 -0700 In-Reply-To: <20240830043600.127750-1-seanjc@google.com> Mime-Version: 1.0 References: <20240830043600.127750-1-seanjc@google.com> X-Mailer: git-send-email 2.46.0.469.g59c65b2a67-goog Message-ID: <20240830043600.127750-2-seanjc@google.com> Subject: [PATCH v4 01/10] KVM: Use dedicated mutex to protect kvm_usage_count to avoid deadlock From: Sean Christopherson To: Paolo Bonzini , Marc Zyngier , Oliver Upton , Tianrui Zhao , Bibo Mao , Huacai Chen , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Sean Christopherson Cc: kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, loongarch@lists.linux.dev, linux-mips@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, Chao Gao , Kai Huang , Farrah Chen X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240829_213608_816103_B0733151 X-CRM114-Status: GOOD ( 20.28 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Sean Christopherson Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Use a dedicated mutex to guard kvm_usage_count to fix a potential deadlock on x86 due to a chain of locks and SRCU synchronizations. Translating the below lockdep splat, CPU1 #6 will wait on CPU0 #1, CPU0 #8 will wait on CPU2 #3, and CPU2 #7 will wait on CPU1 #4 (if there's a writer, due to the fairness of r/w semaphores). CPU0 CPU1 CPU2 1 lock(&kvm->slots_lock); 2 lock(&vcpu->mutex); 3 lock(&kvm->srcu); 4 lock(cpu_hotplug_lock); 5 lock(kvm_lock); 6 lock(&kvm->slots_lock); 7 lock(cpu_hotplug_lock); 8 sync(&kvm->srcu); Note, there are likely more potential deadlocks in KVM x86, e.g. the same pattern of taking cpu_hotplug_lock outside of kvm_lock likely exists with __kvmclock_cpufreq_notifier(): cpuhp_cpufreq_online() | -> cpufreq_online() | -> cpufreq_gov_performance_limits() | -> __cpufreq_driver_target() | -> __target_index() | -> cpufreq_freq_transition_begin() | -> cpufreq_notify_transition() | -> ... __kvmclock_cpufreq_notifier() But, actually triggering such deadlocks is beyond rare due to the combination of dependencies and timings involved. E.g. the cpufreq notifier is only used on older CPUs without a constant TSC, mucking with the NX hugepage mitigation while VMs are running is very uncommon, and doing so while also onlining/offlining a CPU (necessary to generate contention on cpu_hotplug_lock) would be even more unusual. The most robust solution to the general cpu_hotplug_lock issue is likely to switch vm_list to be an RCU-protected list, e.g. so that x86's cpufreq notifier doesn't to take kvm_lock. For now, settle for fixing the most blatant deadlock, as switching to an RCU-protected list is a much more involved change, but add a comment in locking.rst to call out that care needs to be taken when walking holding kvm_lock and walking vm_list. ====================================================== WARNING: possible circular locking dependency detected 6.10.0-smp--c257535a0c9d-pip #330 Tainted: G S O ------------------------------------------------------ tee/35048 is trying to acquire lock: ff6a80eced71e0a8 (&kvm->slots_lock){+.+.}-{3:3}, at: set_nx_huge_pages+0x179/0x1e0 [kvm] but task is already holding lock: ffffffffc07abb08 (kvm_lock){+.+.}-{3:3}, at: set_nx_huge_pages+0x14a/0x1e0 [kvm] which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #3 (kvm_lock){+.+.}-{3:3}: __mutex_lock+0x6a/0xb40 mutex_lock_nested+0x1f/0x30 kvm_dev_ioctl+0x4fb/0xe50 [kvm] __se_sys_ioctl+0x7b/0xd0 __x64_sys_ioctl+0x21/0x30 x64_sys_call+0x15d0/0x2e60 do_syscall_64+0x83/0x160 entry_SYSCALL_64_after_hwframe+0x76/0x7e -> #2 (cpu_hotplug_lock){++++}-{0:0}: cpus_read_lock+0x2e/0xb0 static_key_slow_inc+0x16/0x30 kvm_lapic_set_base+0x6a/0x1c0 [kvm] kvm_set_apic_base+0x8f/0xe0 [kvm] kvm_set_msr_common+0x9ae/0xf80 [kvm] vmx_set_msr+0xa54/0xbe0 [kvm_intel] __kvm_set_msr+0xb6/0x1a0 [kvm] kvm_arch_vcpu_ioctl+0xeca/0x10c0 [kvm] kvm_vcpu_ioctl+0x485/0x5b0 [kvm] __se_sys_ioctl+0x7b/0xd0 __x64_sys_ioctl+0x21/0x30 x64_sys_call+0x15d0/0x2e60 do_syscall_64+0x83/0x160 entry_SYSCALL_64_after_hwframe+0x76/0x7e -> #1 (&kvm->srcu){.+.+}-{0:0}: __synchronize_srcu+0x44/0x1a0 synchronize_srcu_expedited+0x21/0x30 kvm_swap_active_memslots+0x110/0x1c0 [kvm] kvm_set_memslot+0x360/0x620 [kvm] __kvm_set_memory_region+0x27b/0x300 [kvm] kvm_vm_ioctl_set_memory_region+0x43/0x60 [kvm] kvm_vm_ioctl+0x295/0x650 [kvm] __se_sys_ioctl+0x7b/0xd0 __x64_sys_ioctl+0x21/0x30 x64_sys_call+0x15d0/0x2e60 do_syscall_64+0x83/0x160 entry_SYSCALL_64_after_hwframe+0x76/0x7e -> #0 (&kvm->slots_lock){+.+.}-{3:3}: __lock_acquire+0x15ef/0x2e30 lock_acquire+0xe0/0x260 __mutex_lock+0x6a/0xb40 mutex_lock_nested+0x1f/0x30 set_nx_huge_pages+0x179/0x1e0 [kvm] param_attr_store+0x93/0x100 module_attr_store+0x22/0x40 sysfs_kf_write+0x81/0xb0 kernfs_fop_write_iter+0x133/0x1d0 vfs_write+0x28d/0x380 ksys_write+0x70/0xe0 __x64_sys_write+0x1f/0x30 x64_sys_call+0x281b/0x2e60 do_syscall_64+0x83/0x160 entry_SYSCALL_64_after_hwframe+0x76/0x7e Cc: Chao Gao Fixes: 0bf50497f03b ("KVM: Drop kvm_count_lock and instead protect kvm_usage_count with kvm_lock") Cc: stable@vger.kernel.org Reviewed-by: Kai Huang Acked-by: Kai Huang Tested-by: Farrah Chen Signed-off-by: Sean Christopherson --- Documentation/virt/kvm/locking.rst | 32 +++++++++++++++++++++--------- virt/kvm/kvm_main.c | 31 +++++++++++++++-------------- 2 files changed, 39 insertions(+), 24 deletions(-) diff --git a/Documentation/virt/kvm/locking.rst b/Documentation/virt/kvm/locking.rst index 02880d5552d5..c0cb5ce51c1e 100644 --- a/Documentation/virt/kvm/locking.rst +++ b/Documentation/virt/kvm/locking.rst @@ -9,7 +9,7 @@ KVM Lock Overview The acquisition orders for mutexes are as follows: -- cpus_read_lock() is taken outside kvm_lock +- cpus_read_lock() is taken outside kvm_lock and kvm_usage_lock - kvm->lock is taken outside vcpu->mutex @@ -24,6 +24,12 @@ The acquisition orders for mutexes are as follows: are taken on the waiting side when modifying memslots, so MMU notifiers must not take either kvm->slots_lock or kvm->slots_arch_lock. +cpus_read_lock() vs kvm_lock: +- Taking cpus_read_lock() outside of kvm_lock is problematic, despite that + being the official ordering, as it is quite easy to unknowingly trigger + cpus_read_lock() while holding kvm_lock. Use caution when walking vm_list, + e.g. avoid complex operations when possible. + For SRCU: - ``synchronize_srcu(&kvm->srcu)`` is called inside critical sections @@ -227,10 +233,17 @@ time it will be set using the Dirty tracking mechanism described above. :Type: mutex :Arch: any :Protects: - vm_list - - kvm_usage_count + +``kvm_usage_lock`` +^^^^^^^^^^^^^^^^^^ + +:Type: mutex +:Arch: any +:Protects: - kvm_usage_count - hardware virtualization enable/disable -:Comment: KVM also disables CPU hotplug via cpus_read_lock() during - enable/disable. +:Comment: Exists because using kvm_lock leads to deadlock (see earlier comment + on cpus_read_lock() vs kvm_lock). Note, KVM also disables CPU hotplug via + cpus_read_lock() when enabling/disabling virtualization. ``kvm->mn_invalidate_lock`` ^^^^^^^^^^^^^^^^^^^^^^^^^^^ @@ -290,11 +303,12 @@ time it will be set using the Dirty tracking mechanism described above. wakeup. ``vendor_module_lock`` -^^^^^^^^^^^^^^^^^^^^^^^^^^^^ +^^^^^^^^^^^^^^^^^^^^^^ :Type: mutex :Arch: x86 :Protects: loading a vendor module (kvm_amd or kvm_intel) -:Comment: Exists because using kvm_lock leads to deadlock. cpu_hotplug_lock is - taken outside of kvm_lock, e.g. in KVM's CPU online/offline callbacks, and - many operations need to take cpu_hotplug_lock when loading a vendor module, - e.g. updating static calls. +:Comment: Exists because using kvm_lock leads to deadlock. kvm_lock is taken + in notifiers, e.g. __kvmclock_cpufreq_notifier(), that may be invoked while + cpu_hotplug_lock is held, e.g. from cpufreq_boost_trigger_state(), and many + operations need to take cpu_hotplug_lock when loading a vendor module, e.g. + updating static calls. diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 92901656a0d4..b4cdb659d3e1 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -5576,6 +5576,7 @@ __visible bool kvm_rebooting; EXPORT_SYMBOL_GPL(kvm_rebooting); static DEFINE_PER_CPU(bool, hardware_enabled); +static DEFINE_MUTEX(kvm_usage_lock); static int kvm_usage_count; static int __hardware_enable_nolock(void) @@ -5608,10 +5609,10 @@ static int kvm_online_cpu(unsigned int cpu) * be enabled. Otherwise running VMs would encounter unrecoverable * errors when scheduled to this CPU. */ - mutex_lock(&kvm_lock); + mutex_lock(&kvm_usage_lock); if (kvm_usage_count) ret = __hardware_enable_nolock(); - mutex_unlock(&kvm_lock); + mutex_unlock(&kvm_usage_lock); return ret; } @@ -5631,10 +5632,10 @@ static void hardware_disable_nolock(void *junk) static int kvm_offline_cpu(unsigned int cpu) { - mutex_lock(&kvm_lock); + mutex_lock(&kvm_usage_lock); if (kvm_usage_count) hardware_disable_nolock(NULL); - mutex_unlock(&kvm_lock); + mutex_unlock(&kvm_usage_lock); return 0; } @@ -5650,9 +5651,9 @@ static void hardware_disable_all_nolock(void) static void hardware_disable_all(void) { cpus_read_lock(); - mutex_lock(&kvm_lock); + mutex_lock(&kvm_usage_lock); hardware_disable_all_nolock(); - mutex_unlock(&kvm_lock); + mutex_unlock(&kvm_usage_lock); cpus_read_unlock(); } @@ -5683,7 +5684,7 @@ static int hardware_enable_all(void) * enable hardware multiple times. */ cpus_read_lock(); - mutex_lock(&kvm_lock); + mutex_lock(&kvm_usage_lock); r = 0; @@ -5697,7 +5698,7 @@ static int hardware_enable_all(void) } } - mutex_unlock(&kvm_lock); + mutex_unlock(&kvm_usage_lock); cpus_read_unlock(); return r; @@ -5725,13 +5726,13 @@ static int kvm_suspend(void) { /* * Secondary CPUs and CPU hotplug are disabled across the suspend/resume - * callbacks, i.e. no need to acquire kvm_lock to ensure the usage count - * is stable. Assert that kvm_lock is not held to ensure the system - * isn't suspended while KVM is enabling hardware. Hardware enabling - * can be preempted, but the task cannot be frozen until it has dropped - * all locks (userspace tasks are frozen via a fake signal). + * callbacks, i.e. no need to acquire kvm_usage_lock to ensure the usage + * count is stable. Assert that kvm_usage_lock is not held to ensure + * the system isn't suspended while KVM is enabling hardware. Hardware + * enabling can be preempted, but the task cannot be frozen until it has + * dropped all locks (userspace tasks are frozen via a fake signal). */ - lockdep_assert_not_held(&kvm_lock); + lockdep_assert_not_held(&kvm_usage_lock); lockdep_assert_irqs_disabled(); if (kvm_usage_count) @@ -5741,7 +5742,7 @@ static int kvm_suspend(void) static void kvm_resume(void) { - lockdep_assert_not_held(&kvm_lock); + lockdep_assert_not_held(&kvm_usage_lock); lockdep_assert_irqs_disabled(); if (kvm_usage_count)