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 A85EC32573F; Wed, 20 May 2026 23:27:54 +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=1779319676; cv=none; b=i/Qdb5CFarayjN79E9AC4ru0W/uLCgsUsv8Bh59ccvj6hcgkf5zn72cyHWb99m/nK3RVdQKNiDtdQ8kwtQINSaHaF44X2GBHV6ubaEKFNUM83wThuza8uViqpaIIOHoXDa6e9RrJus/ND+ZNBXCm7xSJ93ioBaGzNPEJ06qANLI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779319676; c=relaxed/simple; bh=0UzuSR0lFFJs1N60oRVgd42d8TN/MZ03m79/Hebs0z8=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=nlIdixZ9GTkgu28ErbBVs9Un4tOyK8wcBClB0aBWPpUY8rjt4zMkz5TzRYFMfbt+T6ZSRzqHLQapr5ujJxio3CPxSDeh6LuX4rozSRGg1d37kplpwzUHlW08eTEk4/oQxtaeBtz2YYsvtRXqA2LSFCJaRpOb7jJnCKX+o+TBgzw= 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=VuBJdjEN; 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="VuBJdjEN" 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=0UzuSR0lFFJs1N60oRVgd42d8TN/MZ03m79/Hebs0z8=; b=VuBJdjEN0/uT7sj94JtlpAkBp9 LDdR/TyFbfJKsiSumGNgT740rb91vcwWSgmRTSR6CMc65vxif6nf/7K/BEPlbtJ/mBcP/kyVwe31w psHRWYEdc+o3ePDDb7V7xqxOkMLJW0iy4bREcDCdBtlGV+MCOYotcag5SLX6iXZ403/d8/RkHXIKt 5giThODgbhwwZz+ofkLsuniqBuyHX8Rn9+Hbs1/iYEiV/AC2MtcDgiHdVEgx9pQFQ3uIOLh7Ol32m KOeLiGbhvxvVZdnYnFGzgzHH1duez5FrKcjMDRmfVsR8NJ1MiT6W+/q9R9x8nm4nxvgNBVHMQEYYP 0rSE7VqQ==; Received: from 54-240-197-235.amazon.com ([54.240.197.235] helo=freeip.amazon.com) by casper.infradead.org with esmtpsa (Exim 4.99.1 #2 (Red Hat Linux)) id 1wPqKI-00000007k6c-2Lp0; Wed, 20 May 2026 23:27:46 +0000 Message-ID: <423b37f056f0d4d596d5f4cc73802fb1079ecf63.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 , 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 , 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 Date: Thu, 21 May 2026 00:27:44 +0100 In-Reply-To: <20260515191942.1892718-28-seanjc@google.com> References: <20260515191942.1892718-1-seanjc@google.com> <20260515191942.1892718-28-seanjc@google.com> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-QWJZ7uXErmxFQ92K7UlO" 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 --=-QWJZ7uXErmxFQ92K7UlO Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable 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 will 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 to the MS= R is > technically ok, skip the registration when kvmclock is sched_clock so tha= t > 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 B= oth > KVM (as-a-guest) and timekeeping/clocksource hook syscore_ops, and it's > not super obvious that using KVM's hooks would be flawed.=C2=A0 E.g. it w= ould > 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. >=20 > Opportunsitically make the registration messages more precise to help > debug issues where kvmclock is enabled too late. That's a hard word to type, isn't it? > Opportunstically WARN in kvmclock_{suspend,resume}() to harden against > future bugs. So is that :) > Signed-off-by: Sean Christopherson Reviewed-by: David Woodhouse --=-QWJZ7uXErmxFQ92K7UlO 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 GfZI+LGqSv0YtNa54T9D1AWJy08ZKkWvfGGIXN9UFAPMJ6OLLH/UUEgFa+7KlrEvMUupDFGnnR06 aDJAwtycb8yXtILj+TvfhLFhafxroXrflspavejQkEiHjNjtHnwbZ+o43g0/yxjwnarGI3kgcak7 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