From patchwork Thu Sep 22 18:20:38 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Isaku Yamahata X-Patchwork-Id: 12985649 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 63F02ECAAD8 for ; Thu, 22 Sep 2022 18:21:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232338AbiIVSVg (ORCPT ); Thu, 22 Sep 2022 14:21:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34586 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231479AbiIVSVZ (ORCPT ); Thu, 22 Sep 2022 14:21:25 -0400 Received: from mga05.intel.com (mga05.intel.com [192.55.52.43]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5A89C10AB17; Thu, 22 Sep 2022 11:21:24 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1663870884; x=1695406884; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=48U9dCYj/WeMAxDcm+7eitcQw4Ht0b3752iS3YU0zk8=; b=O1Imqpgp+JYoateUNcb+NiVQ1dhXgU4tDEgdfZrpn8bDP76mr0RPmSc3 jvHJyJGVEBUtsvqQCAJI0ceyj366yN+uFS351rJOk9CIm426SV2S4Wox6 ddt0r2Q3ax2RMCkV6lIAfRPW43s8HhGspMcc9rP4V7PzMDd3z+XYVUdcs 2Aq18wzRd8H8vHuTPcVG4PqqRHfdOux/XWJipwK8X+33UQWxZkBG2u4S3 6lHDnPLuZQ/L+NhiF58zuKFkXJe1sxKd/vv0YI2O98nq/5mZi+5KM4QKg nXduQdiiJe8GsZTUh6ROpphDwp+ZtrpW6LqZus/Lm1c+vcd9dddjz5az0 w==; X-IronPort-AV: E=McAfee;i="6500,9779,10478"; a="386675974" X-IronPort-AV: E=Sophos;i="5.93,337,1654585200"; d="scan'208";a="386675974" Received: from orsmga001.jf.intel.com ([10.7.209.18]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 22 Sep 2022 11:21:17 -0700 X-IronPort-AV: E=Sophos;i="5.93,337,1654585200"; d="scan'208";a="653086696" Received: from ls.sc.intel.com (HELO localhost) ([143.183.96.54]) by orsmga001-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 22 Sep 2022 11:21:17 -0700 From: isaku.yamahata@intel.com To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Paolo Bonzini , Sean Christopherson , Thomas Gleixner , Marc Zyngier , Will Deacon Cc: isaku.yamahata@intel.com, isaku.yamahata@gmail.com, Kai Huang , Chao Gao , Atish Patra , Shaokun Zhang , Daniel Lezcano , Huang Ying , Huacai Chen , Dave Hansen , Borislav Petkov Subject: [PATCH v5 09/30] KVM: Drop kvm_count_lock and instead protect kvm_usage_count with kvm_lock Date: Thu, 22 Sep 2022 11:20:38 -0700 Message-Id: <92836b09c8e0f19f8e506008e45993881d22b6d1.1663869838.git.isaku.yamahata@intel.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: References: MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org From: Isaku Yamahata Because kvm_count_lock unnecessarily complicates the KVM locking convention Drop kvm_count_lock and instead protect kvm_usage_count with kvm_lock for simplicity. kvm_arch_hardware_enable/disable() callbacks depend on non-preemptiblity with the spin lock. Add preempt_disable/enable() around hardware enable/disable callback to keep the assumption. Because kvm_suspend() and kvm_resume() is called with interrupt disabled, they don't need preempt_disable/enable() pair. Opportunistically add some comments on locking. Suggested-by: Sean Christopherson Signed-off-by: Isaku Yamahata --- Documentation/virt/kvm/locking.rst | 14 +++----- virt/kvm/kvm_main.c | 56 +++++++++++++++++++++++------- 2 files changed, 49 insertions(+), 21 deletions(-) diff --git a/Documentation/virt/kvm/locking.rst b/Documentation/virt/kvm/locking.rst index 845a561629f1..55d6559ace2a 100644 --- a/Documentation/virt/kvm/locking.rst +++ b/Documentation/virt/kvm/locking.rst @@ -216,15 +216,11 @@ time it will be set using the Dirty tracking mechanism described above. :Type: mutex :Arch: any :Protects: - vm_list - -``kvm_count_lock`` -^^^^^^^^^^^^^^^^^^ - -:Type: raw_spinlock_t -:Arch: any -:Protects: - hardware virtualization enable/disable -:Comment: 'raw' because hardware enabling/disabling must be atomic /wrt - migration. + - kvm_usage_count + - hardware virtualization enable/disable +:Comment: Use cpus_read_lock() for hardware virtualization enable/disable + because hardware enabling/disabling must be atomic /wrt + CPU hotplug. The lock order is cpus lock => kvm_lock. ``kvm->mn_invalidate_lock`` ^^^^^^^^^^^^^^^^^^^^^^^^^^^ diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index b1bf44af523c..c4b908553726 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -100,7 +100,6 @@ EXPORT_SYMBOL_GPL(halt_poll_ns_shrink); */ DEFINE_MUTEX(kvm_lock); -static DEFINE_RAW_SPINLOCK(kvm_count_lock); LIST_HEAD(vm_list); static cpumask_var_t cpus_hardware_enabled; @@ -4996,6 +4995,8 @@ static void hardware_enable_nolock(void *junk) int cpu = raw_smp_processor_id(); int r; + WARN_ON_ONCE(preemptible()); + if (cpumask_test_cpu(cpu, cpus_hardware_enabled)) return; @@ -5019,7 +5020,7 @@ static int kvm_online_cpu(unsigned int cpu) if (ret) return ret; - raw_spin_lock(&kvm_count_lock); + mutex_lock(&kvm_lock); /* * Abort the CPU online process if hardware virtualization cannot * be enabled. Otherwise running VMs would encounter unrecoverable @@ -5028,13 +5029,20 @@ static int kvm_online_cpu(unsigned int cpu) if (kvm_usage_count) { WARN_ON_ONCE(atomic_read(&hardware_enable_failed)); + /* + * arch callback kvm_arch_hardware_eanble() assumes that + * preemption is disabled for historical reason. Disable + * preemption until all arch callbacks are fixed. + */ + preempt_disable(); hardware_enable_nolock(NULL); + preempt_enable(); if (atomic_read(&hardware_enable_failed)) { atomic_set(&hardware_enable_failed, 0); ret = -EIO; } } - raw_spin_unlock(&kvm_count_lock); + mutex_unlock(&kvm_lock); return ret; } @@ -5042,6 +5050,8 @@ static void hardware_disable_nolock(void *junk) { int cpu = raw_smp_processor_id(); + WARN_ON_ONCE(preemptible()); + if (!cpumask_test_cpu(cpu, cpus_hardware_enabled)) return; cpumask_clear_cpu(cpu, cpus_hardware_enabled); @@ -5050,10 +5060,18 @@ static void hardware_disable_nolock(void *junk) static int kvm_offline_cpu(unsigned int cpu) { - raw_spin_lock(&kvm_count_lock); - if (kvm_usage_count) + mutex_lock(&kvm_lock); + if (kvm_usage_count) { + /* + * arch callback kvm_arch_hardware_disable() assumes that + * preemption is disabled for historical reason. Disable + * preemption until all arch callbacks are fixed. + */ + preempt_disable(); hardware_disable_nolock(NULL); - raw_spin_unlock(&kvm_count_lock); + preempt_enable(); + } + mutex_unlock(&kvm_lock); return 0; } @@ -5068,9 +5086,11 @@ static void hardware_disable_all_nolock(void) static void hardware_disable_all(void) { - raw_spin_lock(&kvm_count_lock); + cpus_read_lock(); + mutex_lock(&kvm_lock); hardware_disable_all_nolock(); - raw_spin_unlock(&kvm_count_lock); + mutex_unlock(&kvm_lock); + cpus_read_unlock(); } static int hardware_enable_all(void) @@ -5088,7 +5108,7 @@ static int hardware_enable_all(void) * Disable CPU hotplug to prevent this case from happening. */ cpus_read_lock(); - raw_spin_lock(&kvm_count_lock); + mutex_lock(&kvm_lock); kvm_usage_count++; if (kvm_usage_count == 1) { @@ -5101,7 +5121,7 @@ static int hardware_enable_all(void) } } - raw_spin_unlock(&kvm_count_lock); + mutex_unlock(&kvm_lock); cpus_read_unlock(); return r; @@ -5708,15 +5728,27 @@ static void kvm_init_debug(void) static int kvm_suspend(void) { - if (kvm_usage_count) + /* + * The caller ensures that CPU hotplug is disabled by + * cpu_hotplug_disable() and other CPUs are offlined. No need for + * locking. + */ + lockdep_assert_not_held(&kvm_lock); + + if (kvm_usage_count) { + /* + * Because kvm_suspend() is called with interrupt disabled, no + * need to disable preemption. + */ hardware_disable_nolock(NULL); + } return 0; } static void kvm_resume(void) { if (kvm_usage_count) { - lockdep_assert_not_held(&kvm_count_lock); + lockdep_assert_not_held(&kvm_lock); hardware_enable_nolock(NULL); } }