From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f201.google.com (mail-pl1-f201.google.com [209.85.214.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0B42D40C7BF for ; Fri, 15 May 2026 19:21:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778872867; cv=none; b=VmxZgQtGpm41YeXwvRBHsh2yLBw8RIWZsCNezxY1gFqpRzLirihdkA7zML0Z1uoj2oh1RmADOo7G0wnlE7P3dIsfEGFIe//3lz4xABKPi/Lu/Qm6MX1AnhpcrGfgPv7BvlEMMAfkbE9bj0RWIZf1j+OBMm88ACawuoC7rRkjRWI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778872867; c=relaxed/simple; bh=zHts7S5ctJxrCQFHnZI66ey/sV4LnssrZ3CfSU2lq1U=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=GCh1oKdOiaaXcL8yJyuOtaQGOrpNCyqmiFHtI1F5U2bg/7ffgslK2zc+/16CbsZ3Swx7xQSlYOGk2+rq17uMkpQxlFR2t0c/fnqrfw7IsYaQJBAq7XDogKkLg3Em6FW6zG7mwKZQp3CRxwZTOv+iBeiGRlZkfWzlP4hg7oEnEPI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=cAPdeFOd; arc=none smtp.client-ip=209.85.214.201 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="cAPdeFOd" Received: by mail-pl1-f201.google.com with SMTP id d9443c01a7336-2baedd2fd43so2574265ad.1 for ; Fri, 15 May 2026 12:21:05 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1778872865; x=1779477665; darn=vger.kernel.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=9y7n0IksKFKFboHRfxCkU+QRldsv6JkfRx9t9kwNLA4=; b=cAPdeFOdNX/JG2MqM9sXcKVx2p33cguDr3E49fB88r+cOHXVHK/qTkjbIN0NPm0JVJ 1ZXQ4eG6z9H3Tb+tAP1FR++KS5r3dso/4o8NSiCzyy1kn32qPdKfau3pil2sTAsMIXQ1 SXvCFJgnqskX6nO8VEjtM1Ru7FsPzNjjVFazT3rUMjeYc+/V2D0FIT2UTid4C63EHlht T9+5k14vD7F+bBNIZr6EScgZPsPAk7CNE5vHlF3yMwpGDpTX/vi5dc1AyE/lWDzhw0pl BXRWn6qCA8gZ4WYPFTEvtTOCdgbvGr+715NlJn3vasNWcwGioeUxT3Hx5ex20pixHkMC ssLw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1778872865; x=1779477665; 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=9y7n0IksKFKFboHRfxCkU+QRldsv6JkfRx9t9kwNLA4=; b=PL1TVxoqFBkH7q6p4dmeK40xfyKXC0vjCmJZBkb1hhGiboeOpzogfi6fzWDNLefLRV 25dYwDHkwGWRKBhuGN0gxBhIr2zAb4Hq06awBjLUQniwffBKmbfSzHm+M8bFEx7Ne+8H 9avOl5h6+x8d621G5Rvjic11+HKhX5aMj3yZ0I1mtneiGsFqqQ9in1hFtop3jVIvcOx3 5tOLNSq8V66WLFqw1BY5wylV+QoBkKrmkuOSrwL5QChzFgDddXqDWNbQIDOh2slT24Hm 5SR95SZ86RgkQabYB5Q/7DJZeD4GtKkjloy7apbZBIWmac3CDC1FDctd2qoM35acmng9 Y56A== X-Forwarded-Encrypted: i=1; AFNElJ+Fh2pUGSSzvMJS1mQT0QvcM4y7nkRrpMkq/LQ1W7ulfcuieefTJz3UZHKq6G+T7qIAUL8=@vger.kernel.org X-Gm-Message-State: AOJu0YyGvGpenfq9fke4jz4iVj1u1/RkayhncJl0F7DXoESsCeLeSef8 WzQwpRDLzEP0Js3+iLXzYOYfdBlyzAKQyGyxfzHIS7kYNuvMOeGeM4s6LFzNmn3GBJSaNXpDZuU GnWHTMA== X-Received: from plnq2.prod.google.com ([2002:a17:902:f782:b0:2bd:7c8c:4ef4]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:903:bc8:b0:2ba:30fb:d777 with SMTP id d9443c01a7336-2bd7e86c408mr40874505ad.6.1778872864946; Fri, 15 May 2026 12:21:04 -0700 (PDT) Reply-To: Sean Christopherson Date: Fri, 15 May 2026 12:19:28 -0700 In-Reply-To: <20260515191942.1892718-1-seanjc@google.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260515191942.1892718-1-seanjc@google.com> X-Mailer: git-send-email 2.54.0.563.g4f69b47b94-goog Message-ID: <20260515191942.1892718-28-seanjc@google.com> Subject: [PATCH v3 27/41] x86/kvmclock: Enable kvmclock on APs during onlining if kvmclock isn't sched_clock From: Sean Christopherson To: Kiryl Shutsemau , Paolo Bonzini , Sean Christopherson , "K. Y. Srinivasan" , Haiyang Zhang , Wei Liu , Dexuan Cui , Long Li , Ajay Kaher , Alexey Makhalov , Jan Kiszka , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Juergen Gross , Daniel Lezcano , Thomas Gleixner , John Stultz Cc: Rick Edgecombe , Vitaly Kuznetsov , Broadcom internal kernel review list , Boris Ostrovsky , Stephen Boyd , x86@kernel.org, linux-coco@lists.linux.dev, kvm@vger.kernel.org, linux-hyperv@vger.kernel.org, virtualization@lists.linux.dev, linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org, Michael Kelley , Tom Lendacky , Nikunj A Dadhania , Thomas Gleixner , David Woodhouse Content-Type: text/plain; charset="UTF-8" In anticipation of making x86_cpuinit.early_percpu_clock_init(), i.e. kvm_setup_secondary_clock(), a dedicated sched_clock hook that will be invoked if and only if kvmclock is set as sched_clock, ensure APs enable their kvmclock during CPU online. While a redundant write to the MSR is technically ok, skip the registration when kvmclock is sched_clock so that it's somewhat obvious that kvmclock *needs* to be enabled during early bringup when it's being used as sched_clock. Plumb in the BSP's resume path purely for documentation purposes. Both KVM (as-a-guest) and timekeeping/clocksource hook syscore_ops, and it's not super obvious that using KVM's hooks would be flawed. E.g. it would work today, because KVM's hooks happen to run after/before timekeeping's hooks during suspend/resume, but that's sheer dumb luck as the order in which syscore_ops are invoked depends entirely on when a subsystem is initialized and thus registers its hooks. Opportunsitically make the registration messages more precise to help debug issues where kvmclock is enabled too late. Opportunstically WARN in kvmclock_{suspend,resume}() to harden against future bugs. Signed-off-by: Sean Christopherson --- arch/x86/include/asm/kvm_para.h | 2 ++ arch/x86/kernel/kvm.c | 24 +++++++++++------- arch/x86/kernel/kvmclock.c | 44 +++++++++++++++++++++++++++------ 3 files changed, 53 insertions(+), 17 deletions(-) diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h index 2adba2aff539..17053d2bf270 100644 --- a/arch/x86/include/asm/kvm_para.h +++ b/arch/x86/include/asm/kvm_para.h @@ -120,6 +120,8 @@ static inline long kvm_sev_hypercall3(unsigned int nr, unsigned long p1, #ifdef CONFIG_KVM_GUEST enum kvm_guest_cpu_action { KVM_GUEST_BSP_SUSPEND, + KVM_GUEST_BSP_RESUME, + KVM_GUEST_AP_ONLINE, KVM_GUEST_AP_OFFLINE, KVM_GUEST_SHUTDOWN, }; diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c index 0131bc1cb459..65c787b1ea03 100644 --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -471,18 +471,24 @@ static void kvm_guest_cpu_offline(enum kvm_guest_cpu_action action) kvmclock_cpu_action(action); } +static int __kvm_cpu_online(unsigned int cpu, enum kvm_guest_cpu_action action) +{ + unsigned long flags; + + local_irq_save(flags); + kvmclock_cpu_action(action); + kvm_guest_cpu_init(); + local_irq_restore(flags); + return 0; +} + +#ifdef CONFIG_SMP + static int kvm_cpu_online(unsigned int cpu) { - unsigned long flags; - - local_irq_save(flags); - kvm_guest_cpu_init(); - local_irq_restore(flags); - return 0; + return __kvm_cpu_online(cpu, KVM_GUEST_AP_ONLINE); } -#ifdef CONFIG_SMP - static DEFINE_PER_CPU(cpumask_var_t, __pv_cpu_mask); static bool pv_tlb_flush_supported(void) @@ -747,7 +753,7 @@ static int kvm_suspend(void *data) static void kvm_resume(void *data) { - kvm_cpu_online(raw_smp_processor_id()); + __kvm_cpu_online(raw_smp_processor_id(), KVM_GUEST_BSP_RESUME); #ifdef CONFIG_ARCH_CPUIDLE_HALTPOLL if (kvm_para_has_feature(KVM_FEATURE_POLL_CONTROL) && has_guest_poll) diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c index e7250d21c672..d3bb281c0805 100644 --- a/arch/x86/kernel/kvmclock.c +++ b/arch/x86/kernel/kvmclock.c @@ -53,6 +53,7 @@ static struct pvclock_vsyscall_time_info *hvclock_mem; DEFINE_PER_CPU(struct pvclock_vsyscall_time_info *, hv_clock_per_cpu); EXPORT_PER_CPU_SYMBOL_GPL(hv_clock_per_cpu); +static bool kvmclock_is_sched_clock; static bool kvmclock_suspended; /* @@ -129,7 +130,7 @@ static void kvm_save_sched_clock_state(void) #ifdef CONFIG_SMP static void kvm_setup_secondary_clock(void) { - kvm_register_clock("secondary cpu clock"); + kvm_register_clock("secondary cpu, sched_clock setup"); } #endif @@ -141,25 +142,51 @@ static void kvm_restore_sched_clock_state(void) static void kvmclock_suspend(struct clocksource *cs) { + if (WARN_ON_ONCE(kvmclock_is_sched_clock)) + return; + kvmclock_suspended = true; kvmclock_disable(); } static void kvmclock_resume(struct clocksource *cs) { + if (WARN_ON_ONCE(kvmclock_is_sched_clock)) + return; + kvmclock_suspended = false; kvm_register_clock("primary cpu, clocksource resume"); } void kvmclock_cpu_action(enum kvm_guest_cpu_action action) { - /* - * Don't disable kvmclock on the BSP during suspend. If kvmclock is - * being used for sched_clock, then it needs to be kept alive until the - * last minute, and restored as quickly as possible after resume. - */ - if (action != KVM_GUEST_BSP_SUSPEND) + switch (action) { + /* + * The BSP's clock is managed via clocksource suspend/resume, + * to ensure it's enabled/disabled when timekeeping needs it + * to be, e.g. before reading wallclock (which uses kvmclock). + */ + case KVM_GUEST_BSP_SUSPEND: + case KVM_GUEST_BSP_RESUME: + break; + case KVM_GUEST_AP_ONLINE: + /* + * Secondary CPUs use dedicated sched_clock hooks to enable + * kvmclock early during bringup, there's nothing to be done + * when during CPU online. + */ + if (kvmclock_is_sched_clock) + break; + kvm_register_clock("secondary cpu, online"); + break; + case KVM_GUEST_AP_OFFLINE: + case KVM_GUEST_SHUTDOWN: kvmclock_disable(); + break; + default: + WARN_ON_ONCE(1); + break; + } } /* @@ -315,6 +342,7 @@ static __init void kvm_sched_clock_init(bool stable) __paravirt_set_sched_clock(kvm_sched_clock_read, stable, kvm_save_sched_clock_state, kvm_restore_sched_clock_state); + kvmclock_is_sched_clock = true; /* * The BSP's clock is managed via dedicated sched_clock save/restore @@ -358,7 +386,7 @@ void __init kvmclock_init(void) msr_kvm_system_time, msr_kvm_wall_clock); this_cpu_write(hv_clock_per_cpu, &hv_clock_boot[0]); - kvm_register_clock("primary cpu clock"); + kvm_register_clock("primary cpu, online"); pvclock_set_pvti_cpu0_va(hv_clock_boot); if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE_STABLE_BIT)) { -- 2.54.0.563.g4f69b47b94-goog