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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 8568FCDB474 for ; Fri, 20 Oct 2023 17:07:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:Cc:To:From:Subject:Message-ID: References:Mime-Version:In-Reply-To:Date:Reply-To:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Owner; bh=40/BvoTJOFrO8DQMk/nD6DYJFGCWrTk8wxIeSOZfNBE=; b=n84jv9loCOHfuF8y/Swy5M7sPo v2bGkDZqHZGqW5BobLG+54yYxjnPw0YD4wy/8mAenQ05M6x7mdvd7oTKuUmi0QuCkXO+fn9T+ZNLV EU3gAhY/3x4r4ZpEQTCzrfvrqb1Mw6JNRIYMD7Dcqzp0mcdkDCsJ40/nDEMw/go0B9xYgfwX7GfCz ZRT6fPATHi0H2YsNLTjYQ2VNWfSPwRi3yMWtxMTs1qypsCFdXBACJF48kjh5kMrLZ6GSRbGM7Mw0s zOr73oP/M2frMR/6QIy1rQtB3vxQ3YhStLOT8aivbZENSVpLs1Wm7bvLO464FD7cheFGSA5DeHkfl CUYU3lgQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1qtsyR-002k9c-2R; Fri, 20 Oct 2023 17:07:47 +0000 Received: from mail-pj1-x1049.google.com ([2607:f8b0:4864:20::1049]) by bombadil.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1qtsyO-002k85-1G for kexec@lists.infradead.org; Fri, 20 Oct 2023 17:07:45 +0000 Received: by mail-pj1-x1049.google.com with SMTP id 98e67ed59e1d1-27779f49458so916162a91.2 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=lists.infradead.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=vJyyTqkgnsdLf+Zg4gXJyngRPpl5/RuF92j1RR6a7mO9jkY8GsmZ2/AjmiZI1I4fE0 na/3L89OYeGr1IeIECOK5cU1mnetTok3QFlJ8Hb7BIUE0qpzXmwC9UhSYDIbOEBMSo9i X25tYHLveMCgJ7kE86YvNZKV6DzFD5QJaCGoEpBhOnpYPW2WY0nVyAHg6g6jtBewFknz ndBBBlj0n/VfbiUP7q/Z+SpvEtV5ldXyoQ+f9EdFfo3ntqG6kAsRgjeMIaE3Fvqdafkx FlxocfxTJ8YqttfguHTZ3l1ewU9qvQhYMozAUJYJYJlrxCQsbbFSi0HobDyJJm/DbJmN nUWQ== 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=tHMVnup3SYml4BnYMhvUU7mU0MLYLJ970cpCvRBq5bDqwD/K9ROif2pXpRYvSEluxd dC2nIYGTahQ3O2z/Bxqjdf6wZtkDJGn87U3hmVyyBzW68Q7g6lv5sV//GJgnrK9yRzOf z6vafNGJOsyZ0Cem49eG7T3zTLRcaAEG3pFJnSPQ5NOUPMlsT8Are2B2ErhuJnl3wfhj 7DTg/MYs0FBoEbnOZcymCawZbkmMQrw4X9sP9OWwKW3aiCqRjbGF8gIMIQ8eslhAsI90 BbO4GZjD9lwv7Yb7/QiE69JR9V7BZoDGadf+P6SmxTBNscrIoB4pQVzAd+FLHFmnSnLp PuJg== X-Gm-Message-State: AOJu0YwbUYpPtfsnkRkRQSOaHqZzBrC02YmjZrQN+G2p4UVWcG3cWN43 o8bh94Z9TVqBxGhjfi/OJ1nP0+Q3nP4= 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 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20231020_100744_456738_384063EC X-CRM114-Status: GOOD ( 23.49 ) X-BeenThere: kexec@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+kexec=archiver.kernel.org@lists.infradead.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(). _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec