From mboxrd@z Thu Jan 1 00:00:00 1970 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 18E81C433FE for ; Wed, 2 Nov 2022 23:26:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231571AbiKBX0r (ORCPT ); Wed, 2 Nov 2022 19:26:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43646 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231440AbiKBXZb (ORCPT ); Wed, 2 Nov 2022 19:25:31 -0400 Received: from mail-yb1-xb49.google.com (mail-yb1-xb49.google.com [IPv6:2607:f8b0:4864:20::b49]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7523311C1F for ; Wed, 2 Nov 2022 16:20:42 -0700 (PDT) Received: by mail-yb1-xb49.google.com with SMTP id 130-20020a251188000000b006be249d0a70so402583ybr.2 for ; Wed, 02 Nov 2022 16:20:42 -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=OIMXqLasKb2O7+CMjQgfYLOt6T5DmXDJujGgVXhHqFI=; b=a1O/5J/wwBHL5DdZlnXyBx3ad/wWPMoFwu33ObN+0h9wckbMWe8lEdCsf3vv9dBpgd Og1tkQtFVeN8Yaq0826BqmvMwQ236D77oay2sYYYSosRusWw8ffouoxC4D4VSugKPkv6 eFSXHeIkk4rxzIyC2jBSOKzzG944O7R7WfzIzWLb9f4+zjzqLEX7pMuEWnereIkmHCla z9Wi0z30aLvdj67Gj18fnOk19FrwVJlssI8qaBiE05oy40Xc5I9xoCB6VMFe6e9n0+Qe iXYDA9B6ROLH1CUwVEa9sH8tNUrl6u56cDEtM0Lb6ytwc6hrZDZzuAPDLoXNIWglaaUo bPHg== 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=OIMXqLasKb2O7+CMjQgfYLOt6T5DmXDJujGgVXhHqFI=; b=06ssTXWnjs89Jjz9QQzHjeBhI0jnqSabXZ3jJyp5GyFXcCwoUCHmXnkw1t0OYRFsXX 9X/vX7KWNrPh2qW/bk0nRMmMA51AlE4FwMG3SL533bBN+tCqtnhVm2DGLbgHB6/6/jCw 2FgUj9hgyimVTFwUyXPl62Vq+ErK17PnvgWCE1kP31kwplB//B5e8/LxOud1Vtz3KYOK ivT/PDjuZ1ciwlwPdS29ZpN+oRBMQ4VJRfefOozjZWb0PBuWy92F0juFm/B/mpjFyUkR ZAf/VbD+qY8TJ9USlPDvDOyJlLt3hvKwyK/2KT9zu2ymI4he+ElkevERE1pmM1nRaOiI Ss8w== X-Gm-Message-State: ACrzQf3hcqdLMI4koo7n9kQ8LOJ9j4TV8/KCeEIb8qvg0mqHpsxUD9zi 2bZ0JdyUuARMrMFBj634i6acXffaIA0= X-Google-Smtp-Source: AMsMyM6yCCCYKkQ3PoeOADSfJNFYsKEgxfAWyhUa6qA376xUH3n8/ExaQ+otuspws7tagrIY8b2ugf0DdfA= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a81:1713:0:b0:36b:3a6b:4b49 with SMTP id 19-20020a811713000000b0036b3a6b4b49mr26413129ywx.500.1667431224514; Wed, 02 Nov 2022 16:20:24 -0700 (PDT) Reply-To: Sean Christopherson Date: Wed, 2 Nov 2022 23:19:08 +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: <20221102231911.3107438-42-seanjc@google.com> Subject: [PATCH 41/44] KVM: Use a per-CPU variable to track which CPUs have enabled virtualization 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 Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org Use a per-CPU variable instead of a shared bitmap to track which CPUs have successfully enabled virtualization hardware. Using a per-CPU bool avoids the need for an additional allocation, and arguably yields easier to read code. Using a bitmap would be advantageous if KVM used it to avoid generating IPIs to CPUs that failed to enable hardware, but that's an extreme edge case and not worth optimizing, and the low level helpers would still want to keep their individual checks as attempting to enable virtualization hardware when it's already enabled can be problematic, e.g. Intel's VMXON will fault. Opportunistically change the order in hardware_enable_nolock() to set the flag if and only if hardware enabling is successful, instead of speculatively setting the flag and then clearing it on failure. Add a comment explaining that the check in hardware_disable_nolock() isn't simply paranoia. Waaay back when, commit 1b6c016818a5 ("KVM: Keep track of which cpus have virtualization enabled"), added the logic as a guards against CPU hotplug racing with hardware enable/disable. Now that KVM has eliminated the race by taking cpu_hotplug_lock for read (via cpus_read_lock()) when enabling or disabling hardware, at first glance it appears that the check is now superfluous, i.e. it's tempting to remove the per-CPU flag entirely... Signed-off-by: Sean Christopherson --- virt/kvm/kvm_main.c | 41 ++++++++++++++++++----------------------- 1 file changed, 18 insertions(+), 23 deletions(-) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 4a42b78bfb0e..31949a89fe25 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -102,7 +102,7 @@ EXPORT_SYMBOL_GPL(halt_poll_ns_shrink); DEFINE_MUTEX(kvm_lock); LIST_HEAD(vm_list); -static cpumask_var_t cpus_hardware_enabled; +static DEFINE_PER_CPU(bool, hardware_enabled); static int kvm_usage_count; static atomic_t hardware_enable_failed; @@ -5008,21 +5008,17 @@ static struct miscdevice kvm_dev = { static void hardware_enable_nolock(void *junk) { - int cpu = raw_smp_processor_id(); - int r; - - if (cpumask_test_cpu(cpu, cpus_hardware_enabled)) + if (__this_cpu_read(hardware_enabled)) return; - cpumask_set_cpu(cpu, cpus_hardware_enabled); - - r = kvm_arch_hardware_enable(); - - if (r) { - cpumask_clear_cpu(cpu, cpus_hardware_enabled); + if (kvm_arch_hardware_enable()) { atomic_inc(&hardware_enable_failed); - pr_info("kvm: enabling virtualization on CPU%d failed\n", cpu); + pr_info("kvm: enabling virtualization on CPU%d failed\n", + raw_smp_processor_id()); + return; } + + __this_cpu_write(hardware_enabled, true); } static int kvm_online_cpu(unsigned int cpu) @@ -5054,12 +5050,16 @@ static int kvm_online_cpu(unsigned int cpu) static void hardware_disable_nolock(void *junk) { - int cpu = raw_smp_processor_id(); - - if (!cpumask_test_cpu(cpu, cpus_hardware_enabled)) + /* + * Note, hardware_disable_all_nolock() tells all online CPUs to disable + * hardware, not just CPUs that successfully enabled hardware! + */ + if (!__this_cpu_read(hardware_enabled)) return; - cpumask_clear_cpu(cpu, cpus_hardware_enabled); + kvm_arch_hardware_disable(); + + __this_cpu_write(hardware_enabled, false); } static int kvm_offline_cpu(unsigned int cpu) @@ -5861,13 +5861,11 @@ int kvm_init(unsigned vcpu_size, unsigned vcpu_align, struct module *module) int r; int cpu; - if (!zalloc_cpumask_var(&cpus_hardware_enabled, GFP_KERNEL)) - return -ENOMEM; - r = cpuhp_setup_state_nocalls(CPUHP_AP_KVM_ONLINE, "kvm/cpu:online", kvm_online_cpu, kvm_offline_cpu); if (r) - goto out_free_2; + return r; + register_reboot_notifier(&kvm_reboot_notifier); /* A kmem cache lets us meet the alignment requirements of fx_save. */ @@ -5940,8 +5938,6 @@ int kvm_init(unsigned vcpu_size, unsigned vcpu_align, struct module *module) out_free_3: unregister_reboot_notifier(&kvm_reboot_notifier); cpuhp_remove_state_nocalls(CPUHP_AP_KVM_ONLINE); -out_free_2: - free_cpumask_var(cpus_hardware_enabled); return r; } EXPORT_SYMBOL_GPL(kvm_init); @@ -5967,7 +5963,6 @@ void kvm_exit(void) unregister_reboot_notifier(&kvm_reboot_notifier); cpuhp_remove_state_nocalls(CPUHP_AP_KVM_ONLINE); kvm_irqfd_exit(); - free_cpumask_var(cpus_hardware_enabled); } EXPORT_SYMBOL_GPL(kvm_exit); -- 2.38.1.431.g37b22c650d-goog