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 010E9CDB474 for ; Fri, 20 Oct 2023 17:07:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1377837AbjJTRHk (ORCPT ); Fri, 20 Oct 2023 13:07:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56724 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229522AbjJTRHi (ORCPT ); Fri, 20 Oct 2023 13:07:38 -0400 Received: from mail-pj1-x104a.google.com (mail-pj1-x104a.google.com [IPv6:2607:f8b0:4864:20::104a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id ED333A3 for ; Fri, 20 Oct 2023 10:07:36 -0700 (PDT) Received: by mail-pj1-x104a.google.com with SMTP id 98e67ed59e1d1-27779f49458so916164a91.2 for ; Fri, 20 Oct 2023 10:07:36 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1697821656; x=1698426456; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=x4BWurQpapK412rcDC+pUyHudLjLoftq7UvjlE0wpgY=; b=LKFuLI8QH7jcz8atySd85fQrc6cGMXwxm2hvQ4z2PXbxZITY5blOeTTRAj8tWWxuC4 h0kAzWEvA9lBKXWQsQwri/k+aLffpsuVaIq9+W8aPY+3HbbiSQzJlP9vzWBUSikVWn3U W+dncEOJvoQg2qWYwsXH7KRW62RMhUuxbGd9AMdODPEphCkoE6MgISK9yIM3VuxDpCWV DQWgSCPVkqBwJnxoXLHZ5h66KTGIOW6tIpVu9064tluIINHwExkPMmPHj84ta0XJxlJ8 +gsCUrT4RMJrmPR+EXPfPNrlRYglIrXUbfOg+NOMjCqAMOtRyJEbS8R6dNfuUvF4tgmT ae3g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1697821656; x=1698426456; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=x4BWurQpapK412rcDC+pUyHudLjLoftq7UvjlE0wpgY=; b=hD/0uH/tx2lgUwFWBQrvRzxqp17ri1G3b7U6o+2b/7NZ3Y2z44vYu4BQ63IfifgjcF xd5o5kQ3t6loER4AH1tDPvAwxlTkXUKLTuns0X4MYaHpMAHVqlS2Jcpwc6HWj7owMnk/ ahFc7UUUwUDdkUqdqViVzy5DRODF/VosUEeuHfnvlTCub6y7j9ipCWbmsxpjRlgs5bYq pPycKn72ZcdGGE/88Km6bNVWOAxshEVsvsukMgFL8NF2hKLTbYLMsAxwszGdUFlx7/rT iLKdLN7cI46R7BKTapI0nS6lKvOcecvR0dxT3h46OP+Ziw7QGk214n6eCFEFP6ZEM86L 3nzw== X-Gm-Message-State: AOJu0YxuwCdF0NkznXHJjSDJn9lhH20lR2Np1/CkBQMumZWmXVKIN55c NoAx9zpFFrios8KuVzj+U1nVsEq2iX0= X-Google-Smtp-Source: AGHT+IFD7JzGLSjKGr2CZcLV495hcYva5IMtUI4k4GCi8eJrVOm0W02oUecMyWYmDKA2AFrypQyXMTC0gf8= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a17:90a:ab88:b0:277:3135:bc4f with SMTP id n8-20020a17090aab8800b002773135bc4fmr57158pjq.1.1697821656319; Fri, 20 Oct 2023 10:07:36 -0700 (PDT) Date: Fri, 20 Oct 2023 17:07:34 +0000 In-Reply-To: <87wmvh47zb.fsf@redhat.com> Mime-Version: 1.0 References: <20231020151242.1814-1-kirill.shutemov@linux.intel.com> <20231020151242.1814-5-kirill.shutemov@linux.intel.com> <87wmvh47zb.fsf@redhat.com> Message-ID: Subject: Re: [PATCHv2 04/13] x86/kvm: Do not try to disable kvmclock if it was not enabled From: Sean Christopherson To: Vitaly Kuznetsov Cc: "Kirill A. Shutemov" , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "Rafael J. Wysocki" , Peter Zijlstra , Adrian Hunter , Kuppuswamy Sathyanarayanan , Elena Reshetova , Jun Nakajima , Rick Edgecombe , Tom Lendacky , Ashish Kalra , Kai Huang , Baoquan He , kexec@lists.infradead.org, linux-coco@lists.linux.dev, linux-kernel@vger.kernel.org, Paolo Bonzini , Wanpeng Li Content-Type: text/plain; charset="us-ascii" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Oct 20, 2023, Vitaly Kuznetsov wrote: > > --- > > arch/x86/kernel/kvmclock.c | 12 ++++++++---- > > 1 file changed, 8 insertions(+), 4 deletions(-) > > > > diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c > > index fb8f52149be9..f2fff625576d 100644 > > --- a/arch/x86/kernel/kvmclock.c > > +++ b/arch/x86/kernel/kvmclock.c > > @@ -24,8 +24,8 @@ > > > > static int kvmclock __initdata = 1; > > static int kvmclock_vsyscall __initdata = 1; > > -static int msr_kvm_system_time __ro_after_init = MSR_KVM_SYSTEM_TIME; > > -static int msr_kvm_wall_clock __ro_after_init = MSR_KVM_WALL_CLOCK; > > +static int msr_kvm_system_time __ro_after_init; > > +static int msr_kvm_wall_clock __ro_after_init; > > static u64 kvm_sched_clock_offset __ro_after_init; > > > > static int __init parse_no_kvmclock(char *arg) > > @@ -195,7 +195,8 @@ static void kvm_setup_secondary_clock(void) > > > > void kvmclock_disable(void) > > { > > - native_write_msr(msr_kvm_system_time, 0, 0); > > + if (msr_kvm_system_time) > > + native_write_msr(msr_kvm_system_time, 0, 0); > > } > > > > static void __init kvmclock_init_mem(void) > > @@ -294,7 +295,10 @@ void __init kvmclock_init(void) > > if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE2)) { > > msr_kvm_system_time = MSR_KVM_SYSTEM_TIME_NEW; > > msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK_NEW; > > - } else if (!kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) { > > + } else if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) { > > + msr_kvm_system_time = MSR_KVM_SYSTEM_TIME; > > + msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK; > > + } else { > > return; > > } > > This should work, so > > Reviewed-by: Vitaly Kuznetsov > > but my personal preference would be to change kvm_guest_cpu_offline() > to check KVM features explicitly instead of checking MSRs against '0' > at least becase it already does so for other features. Completely > untested: > > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c > index b8ab9ee5896c..1ee49c98e70a 100644 > --- a/arch/x86/kernel/kvm.c > +++ b/arch/x86/kernel/kvm.c > @@ -454,7 +454,9 @@ static void kvm_guest_cpu_offline(bool shutdown) > kvm_pv_disable_apf(); > if (!shutdown) > apf_task_wake_all(); > - kvmclock_disable(); > + if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE2) || > + kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) > + kvmclock_disable(); > } That would result in an unnecessray WRMSR in the case where kvmclock is disabled on the command line. It _should_ be benign given how the code is written, but it's not impossible to imagine a scenario where someone disabled kvmclock in the guest because of a hypervisor bug. And the WRMSR would become a bogus write to MSR 0x0 if someone made a "cleanup" to set msr_kvm_system_time if and only if kvmclock is actually used, e.g. if someone made Kirill's change sans the check in kvmclock_disable().