From nobody Fri Apr 10 20:28:26 2026 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 9EA93C32774 for ; Sat, 20 Aug 2022 06:01:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244963AbiHTGBA (ORCPT ); Sat, 20 Aug 2022 02:01:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47478 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244217AbiHTGAu (ORCPT ); Sat, 20 Aug 2022 02:00:50 -0400 Received: from mga05.intel.com (mga05.intel.com [192.55.52.43]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D8DBBA260A; Fri, 19 Aug 2022 23:00:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1660975249; x=1692511249; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=0AYhMY6fJqrli/t5ys1IPzbYaiXeLEr/7lceDSDM3tw=; b=FMFKAOJX+8eiMsYlL5ED4+LvG1wf1iZI2/QkTFtYsejdBIaXlefKTAO/ CCfhIpRM7PkLChoOzdQ75avpV4PBHi4jplpPP17W1VNHINkfJciBw36DJ gPa56ruf2mHwTvEhQ66eRvJdglJWtz6lqpQjNng3n0ichMrcnHdSNtRYT qvcWnn3cxb6FQ+RK9HE3Cvd7K9JrGVBMArmIyxJKo4B86WvaZLq8SzW7C Bt2shy0JQ/lHlpjrROsb04GliTklxbDR+7nFhfsKRZFi7h8skHWp56E7f vNXGCznFsShm3ZBYkU0Z1XaP+UAYmgb4ANzUrTasmpehAZ4VC+6DevXIT A==; X-IronPort-AV: E=McAfee;i="6500,9779,10444"; a="379448969" X-IronPort-AV: E=Sophos;i="5.93,250,1654585200"; d="scan'208";a="379448969" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Aug 2022 23:00:48 -0700 X-IronPort-AV: E=Sophos;i="5.93,250,1654585200"; d="scan'208";a="668857517" Received: from ls.sc.intel.com (HELO localhost) ([143.183.96.54]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Aug 2022 23:00:48 -0700 From: isaku.yamahata@intel.com To: kvm@vger.kernel.org, linux-kernel@vger.kernel.org Cc: isaku.yamahata@intel.com, isaku.yamahata@gmail.com, Paolo Bonzini , Sean Christopherson , Kai Huang , Chao Gao , Will Deacon Subject: [RFC PATCH 03/18] KVM: Drop kvm_count_lock and instead protect kvm_usage_count with kvm_lock Date: Fri, 19 Aug 2022 23:00:09 -0700 Message-Id: <6b07c02dd361f834fea442eb8dae53f23618f983.1660974106.git.isaku.yamahata@intel.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" 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. 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 | 36 +++++++++++++++++++++--------- 2 files changed, 30 insertions(+), 20 deletions(-) diff --git a/Documentation/virt/kvm/locking.rst b/Documentation/virt/kvm/lo= cking.rst index 845a561629f1..8957e32aa724 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 mechanis= m 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 + migration. The lock order is cpus lock =3D> kvm_lock. =20 ``kvm->mn_invalidate_lock`` ^^^^^^^^^^^^^^^^^^^^^^^^^^^ diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 515dfe9d3bcf..c6781fa30461 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -100,7 +100,6 @@ EXPORT_SYMBOL_GPL(halt_poll_ns_shrink); */ =20 DEFINE_MUTEX(kvm_lock); -static DEFINE_RAW_SPINLOCK(kvm_count_lock); LIST_HEAD(vm_list); =20 static cpumask_var_t cpus_hardware_enabled; @@ -4999,6 +4998,8 @@ static void hardware_enable_nolock(void *junk) int cpu =3D raw_smp_processor_id(); int r; =20 + WARN_ON_ONCE(preemptible()); + if (cpumask_test_cpu(cpu, cpus_hardware_enabled)) return; =20 @@ -5015,10 +5016,10 @@ static void hardware_enable_nolock(void *junk) =20 static int kvm_starting_cpu(unsigned int cpu) { - raw_spin_lock(&kvm_count_lock); + mutex_lock(&kvm_lock); if (kvm_usage_count) hardware_enable_nolock(NULL); - raw_spin_unlock(&kvm_count_lock); + mutex_unlock(&kvm_lock); return 0; } =20 @@ -5026,6 +5027,8 @@ static void hardware_disable_nolock(void *junk) { int cpu =3D raw_smp_processor_id(); =20 + WARN_ON_ONCE(preemptible()); + if (!cpumask_test_cpu(cpu, cpus_hardware_enabled)) return; cpumask_clear_cpu(cpu, cpus_hardware_enabled); @@ -5034,10 +5037,10 @@ static void hardware_disable_nolock(void *junk) =20 static int kvm_dying_cpu(unsigned int cpu) { - raw_spin_lock(&kvm_count_lock); + mutex_lock(&kvm_lock); if (kvm_usage_count) hardware_disable_nolock(NULL); - raw_spin_unlock(&kvm_count_lock); + mutex_unlock(&kvm_lock); return 0; } =20 @@ -5052,16 +5055,19 @@ static void hardware_disable_all_nolock(void) =20 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(); } =20 static int hardware_enable_all(void) { int r =3D 0; =20 - raw_spin_lock(&kvm_count_lock); + cpus_read_lock(); + mutex_lock(&kvm_lock); =20 kvm_usage_count++; if (kvm_usage_count =3D=3D 1) { @@ -5074,7 +5080,8 @@ static int hardware_enable_all(void) } } =20 - raw_spin_unlock(&kvm_count_lock); + mutex_unlock(&kvm_lock); + cpus_read_unlock(); =20 return r; } @@ -5680,15 +5687,22 @@ static void kvm_init_debug(void) =20 static int kvm_suspend(void) { - if (kvm_usage_count) + /* + * The caller ensures that CPU hotlug is disabled by + * cpu_hotplug_disable() and other CPUs are offlined. No need for + * locking. + */ + if (kvm_usage_count) { + lockdep_assert_not_held(&kvm_lock); hardware_disable_nolock(NULL); + } return 0; } =20 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); } } --=20 2.25.1