From patchwork Wed Nov 30 23:09:30 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sean Christopherson X-Patchwork-Id: 13060684 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 66356C4321E for ; Wed, 30 Nov 2022 23:17:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230080AbiK3XRg (ORCPT ); Wed, 30 Nov 2022 18:17:36 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60288 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230328AbiK3XRO (ORCPT ); Wed, 30 Nov 2022 18:17:14 -0500 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 E91A797912 for ; Wed, 30 Nov 2022 15:11:56 -0800 (PST) Received: by mail-yb1-xb4a.google.com with SMTP id y133-20020a25328b000000b006f997751950so5101776yby.7 for ; Wed, 30 Nov 2022 15:11:56 -0800 (PST) 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=CIVhF304FuNQHCB0Z/ANdcEHcyexrW00nsg3ZbCG6ks=; b=WxyXo6El3AY3uS2CCE8493fXu5Xim7YHqqUPh5hzzujrZqyuJESfWenTy3nM6goYlp Z9t0u1cXbo7QWoXuGL3MuNsbCmhLbbziVjnZasLEcNF5XDaOA82dzqNjxV6bd+ZXrBOC /ouUqQeBN7042wSndX+tSRiQP6X7P+98Su9Dei0Z17rkfvZAd/jLirbP5QBkwrW3aWKt 1igXOjcHEfQeCGZapH0wZ1BZKBga5N9z/Z6l5lhjCwpkIDHHLigwALPJgAk7OvgTgEjH y+VeL/ZtkLtUj/8FA5qjJYzxmjn4cU7jTfcqyGA+KImrdI9VHKKYtcoYCpwItGcZ4cNZ q+PA== 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=CIVhF304FuNQHCB0Z/ANdcEHcyexrW00nsg3ZbCG6ks=; b=8JCmzewMFWU0SyVr+Fu3X+XAQgpqQ0HwpW4t8ZRxi6YBBJrt2tOzJLMfqDPi5OVzuO bMnbypzRUQtLBAt62KudUHoexQcf4g3FHnh+I0DuYhsVrRwbYevOOiNsI6wVrtfr0SCx ul//iRpamfQqmi29PcjKi/590jN7Ux8V+vqWIfsqf4/k9ao8O2hqQAVunss1UhAT0cCu ydIaYBNn0P8z2I4XJdETuksqTZSV8lyhqRXF6xV768sjPLPgfQfSQwd87lFZb5yLvGlQ Yoq7y9TOoTHT5EEkr3zsCf/FPK9bRHGRXT/p+XtI2veGYND0JF9H7+Ste6SlR2zKzwoM i93Q== X-Gm-Message-State: ANoB5plpZaxp0slEGbKAR638Jinrsb3h+uMzCUgXeOWQN2h+k/I8u7sQ dhz4Dw+jMF+pZaJd+q7BgsD2wZgtKug= X-Google-Smtp-Source: AA0mqf4TEmJmGOhumywvokE0rv0nuh+lBrITum4tft1lpQQWM3mKCYwOKeeHTdy7a16GXjVSX22jSKiu+4I= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a25:d30b:0:b0:6f9:3655:7a59 with SMTP id e11-20020a25d30b000000b006f936557a59mr8795192ybf.443.1669849857534; Wed, 30 Nov 2022 15:10:57 -0800 (PST) Reply-To: Sean Christopherson Date: Wed, 30 Nov 2022 23:09:30 +0000 In-Reply-To: <20221130230934.1014142-1-seanjc@google.com> Mime-Version: 1.0 References: <20221130230934.1014142-1-seanjc@google.com> X-Mailer: git-send-email 2.38.1.584.g0f3c55d4c2-goog Message-ID: <20221130230934.1014142-47-seanjc@google.com> Subject: [PATCH v2 46/50] 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 , David Woodhouse , Paul Durrant 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, Yuan Yao , Cornelia Huck , Isaku Yamahata , " =?utf-8?q?Philippe_Mathieu-Daud=C3=A9?= " , Fabiano Rosas , Michael Ellerman , Kai Huang , Chao Gao , Thomas Gleixner 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 a27ded004644..c1e48c18e2d9 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; @@ -5027,21 +5027,17 @@ static struct miscdevice kvm_dev = { static void hardware_enable_nolock(void *junk) { - int cpu = 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) @@ -5070,12 +5066,16 @@ static int kvm_online_cpu(unsigned int cpu) static void hardware_disable_nolock(void *junk) { - int cpu = 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) @@ -5876,13 +5876,11 @@ 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. */ @@ -5955,8 +5953,6 @@ 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); @@ -5982,7 +5978,6 @@ 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);