From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 604F32BE7BE; Thu, 21 May 2026 14:13:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779372828; cv=none; b=OAqL7AG0XudzdByqNcKpTMKjzg8LGFQOnGwJSN1oKMcSLoDWnrlsfVa0fnoR2YYNzRMKp9SEyX06NGS71nEwJnVgvD/5a7w/BlbvuRxaf7d+EpgodM63rUzadw0aOOOONCiNv+YIidxbGHBBKIB6a0misppAz6dKK7J36M/e/w0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779372828; c=relaxed/simple; bh=Ma4rUXxctxkBftmjMkUa1ZjNAzu1G4mVje5WD9fbAWQ=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=VKEdYBxyaEJb2+7fykB1RDMh5/+PXwdw3jFa4HynZyYKWGL0iauNAicZMT8Wyu5XAQM3dW7ACjJ9jnhkpev/odZSw3+ecIemcGVLvRixdrDEceyE0BufOn2Fs59dzusO4hW7k6zTeSwle3ORFXfOMcaHuQ+dnELlhT/WEmCMUZs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=casper.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=CSe7eIl3; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=casper.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="CSe7eIl3" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=MIME-Version:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=Ma4rUXxctxkBftmjMkUa1ZjNAzu1G4mVje5WD9fbAWQ=; b=CSe7eIl3b9aaKU3qvbReR7GGlx TvFYVP+wbeuYlAI6cAn2jdlkw0yqpFub5sWNPQghqq18UMXyDmvmuuGjf2wgJ/7aUedA3wf+XZtg8 QuDlLJmdEedu/ZAx2g6D4kwFpgXbVAnC6lIEho0XzXjHYPWGD07pN9WW4VGTrBH3Q3jWU4pa2uUon phWtYIwJitJTjVUKaZLrfVfWZlx4wmJ1oGiaY3Vrggo1gK9O5Ex50Iz6MlEhhr2ZtFM9ab8IWHn6/ gvrmLjB3inwVsMPCOtkjq1d2NWIb+P1kLFDGXJqHbtHBRgX3/HzVyxucukR1qdEVr0GzxxVDPBUP1 SVeYlqIw==; Received: from 54-240-197-239.amazon.com ([54.240.197.239] helo=u09cd745991455d.ant.amazon.com) by casper.infradead.org with esmtpsa (Exim 4.99.1 #2 (Red Hat Linux)) id 1wQ49a-00000008Zoj-333x; Thu, 21 May 2026 14:13:38 +0000 Message-ID: <6d37802ec33601d6be0eb648156e985545b2364a.camel@infradead.org> Subject: Re: [PATCH v3 27/41] x86/kvmclock: Enable kvmclock on APs during onlining if kvmclock isn't sched_clock From: David Woodhouse To: Sean Christopherson , Peter Zijlstra Cc: Kiryl Shutsemau , Paolo Bonzini , "K. Y. Srinivasan" , Haiyang Zhang , Wei Liu , Dexuan Cui , Long Li , Ajay Kaher , Alexey Makhalov , Jan Kiszka , Dave Hansen , Andy Lutomirski , Juergen Gross , Daniel Lezcano , Thomas Gleixner , John Stultz , 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 Date: Thu, 21 May 2026 15:13:37 +0100 In-Reply-To: References: <20260515191942.1892718-1-seanjc@google.com> <20260515191942.1892718-28-seanjc@google.com> <423b37f056f0d4d596d5f4cc73802fb1079ecf63.camel@infradead.org> <20260521131019.GI3126523@noisy.programming.kicks-ass.net> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-/luWii/cRDq/zhkGKorZ" User-Agent: Evolution 3.52.3-0ubuntu1.1 Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org. See http://www.infradead.org/rpr.html --=-/luWii/cRDq/zhkGKorZ Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, 2026-05-21 at 06:38 -0700, Sean Christopherson wrote: > On Thu, May 21, 2026, Peter Zijlstra wrote: > > On Thu, May 21, 2026 at 05:59:17AM -0700, Sean Christopherson wrote: > > > On Thu, May 21, 2026, David Woodhouse wrote: > > > > On Fri, 2026-05-15 at 12:19 -0700, Sean Christopherson wrote: > > > > > In anticipation of making x86_cpuinit.early_percpu_clock_init(), = i.e. > > > > > kvm_setup_secondary_clock(), a dedicated sched_clock hook that wi= ll be > > > > > invoked if and only if kvmclock is set as sched_clock, ensure APs= enable > > > > > their kvmclock during CPU online.=C2=A0 While a redundant write t= o the MSR is > > > > > technically ok, skip the registration when kvmclock is sched_cloc= k so that > > > > > it's somewhat obvious that kvmclock *needs* to be enabled during = early > > > > > bringup when it's being used as sched_clock. > > > > >=20 > > > > > Plumb in the BSP's resume path purely for documentation purposes.= =C2=A0 Both > > > > > KVM (as-a-guest) and timekeeping/clocksource hook syscore_ops, an= d it's > > > > > not super obvious that using KVM's hooks would be flawed.=C2=A0 E= .g. it would > > > > > work today, because KVM's hooks happen to run after/before timeke= eping's > > > > > hooks during suspend/resume, but that's sheer dumb luck as the or= der in > > > > > which syscore_ops are invoked depends entirely on when a subsyste= m is > > > > > initialized and thus registers its hooks. > > > > >=20 > > > > > Opportunsitically make the registration messages more precise to = help > > > > > debug issues where kvmclock is enabled too late. > > > >=20 > > > > That's a hard word to type, isn't it? > > >=20 > > > Heh, you have no idea.=C2=A0 I've been "this" close to creating a VIM= binding for a > > > while, it is time... > >=20 > > 'z=3D' not good enough? >=20 > You people and your fancy ways.=C2=A0 I'm just happy I can get in and out= of the editor :-) I reached the peak of my vi knowledge in about 1995 when I learned that I could log in on another terminal, kill it from there, and then set EDITOR=3Demacs. Ironically I still find myself doing that kind of thing when I'm composing a git-send-email cover letter and decide I don't want to send the series as-is at all. Maybe there's a way to put a poison pill in the message (or save it unchanged?) to make git *NOT* send anything... but I always err on the side of caution and just nuke it from orbit, or at least from another terminal. --=-/luWii/cRDq/zhkGKorZ Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCD9Aw ggSOMIIDdqADAgECAhAOmiw0ECVD4cWj5DqVrT9PMA0GCSqGSIb3DQEBCwUAMGUxCzAJBgNVBAYT AlVTMRUwEwYDVQQKEwxEaWdpQ2VydCBJbmMxGTAXBgNVBAsTEHd3dy5kaWdpY2VydC5jb20xJDAi BgNVBAMTG0RpZ2lDZXJ0IEFzc3VyZWQgSUQgUm9vdCBDQTAeFw0yNDAxMzAwMDAwMDBaFw0zMTEx MDkyMzU5NTlaMEExCzAJBgNVBAYTAkFVMRAwDgYDVQQKEwdWZXJva2V5MSAwHgYDVQQDExdWZXJv a2V5IFNlY3VyZSBFbWFpbCBHMjCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAMjvgLKj jfhCFqxYyRiW8g3cNFAvltDbK5AzcOaR7yVzVGadr4YcCVxjKrEJOgi7WEOH8rUgCNB5cTD8N/Et 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