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 62AC8369D7E; Wed, 20 May 2026 18:52:21 +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=1779303143; cv=none; b=mo+BWdLkJisEX0K6wQieIcmz7c6yThtVWlS+BdBkuWghls0bxECq34f0Ir3ctsLoQcpkQYia4VeNeIIwSu3R4i8/kk7zPeaY3yIKMA8DO7+xH8D3kdKMfeylrA3lMXxP4Tj+80fn9qV5AUpwwiu++GwgPaeKkbYWXLp+CY2ppYo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779303143; c=relaxed/simple; bh=QjAnceuew11RIwWs2DQFFNl23Bhtsg/GKQH/i+NDfAM=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=NH802Dirjl/+lVhsmbe2NuvsAZE4bNk+k80Gs1QR9s3qbuqHl0Eiub/pNhesVCqZKImfyswyEgq8x+ihXkmijf1I65fSuCG+W0ULhmC7+UOzN8BnR9BEXK1VXrJZPVHKpzG1bVBNsQHeaWA0dTez3rLb2CiWMJ9Re6gSCrVwlJU= 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=lgUr7i8E; 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="lgUr7i8E" 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=eRikeJAaevbA4NP2g19rUNwI2NZyhVnTYBWtQ7dcaAU=; b=lgUr7i8EL2F8QaWtzohapoINjb dAnsORiobdYMPtmsSDZ/QRiN7s1rJUCLo9RKbLoIg7hISvL/AVEQZV+KPYSUfrPlPLBx6WxW38sGS StE/N1VLLOq2EXBHiHp5tpuj4XnsA94KqqySKjvCZH1818yr33rWd2lt3i8Z7+V5eDgAVvzdgankH o6qQUd23ZxwUk68fsqyexc2ORewi6gkpiiPpEOsilLASL6yk5nr0Xj2C2toi+f9IuAfZLfUPegn0l dMC3Fcyo7XJFJ3v8+0OXg/iwVZLcN5GdGUs4G5fr4w3PaILbl4vVz1q0UuQpfAUDYMnvOFqzrUtKR sQuhKA1A==; Received: from 54-240-197-227.amazon.com ([54.240.197.227] helo=freeip.amazon.com) by casper.infradead.org with esmtpsa (Exim 4.99.1 #2 (Red Hat Linux)) id 1wPm1d-00000007UNm-3bew; Wed, 20 May 2026 18:52:14 +0000 Message-ID: <0a3aa07a1d3c4bec2b89f8026093969155b73caa.camel@infradead.org> Subject: Re: [PATCH v3 41/41] x86/kvmclock: Get CPU base frequency from CPUID when it's available 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: Wed, 20 May 2026 19:52:12 +0100 In-Reply-To: <20260515191942.1892718-42-seanjc@google.com> References: <20260515191942.1892718-1-seanjc@google.com> <20260515191942.1892718-42-seanjc@google.com> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-iph/FD/9Oere6U4F6y6S" 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 --=-iph/FD/9Oere6U4F6y6S Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Fri, 2026-05-15 at 12:19 -0700, Sean Christopherson wrote: > If CPUID.0x16 is present and valid, use the CPU frequency provided by > CPUID instead of assuming that the virtual CPU runs at the same > frequency as TSC and/or kvmclock.=C2=A0 Back before constant TSCs were a > thing, treating the TSC and CPU frequencies as one and the same was > somewhat reasonable, but now it's nonsensical, especially if the > hypervisor explicitly enumerates the CPU frequency. >=20 > Signed-off-by: Sean Christopherson > --- > =C2=A0arch/x86/kernel/kvmclock.c | 16 +++++++++++++++- > =C2=A01 file changed, 15 insertions(+), 1 deletion(-) >=20 > diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c > index 62c8ea2e6769..7607920ae386 100644 > --- a/arch/x86/kernel/kvmclock.c > +++ b/arch/x86/kernel/kvmclock.c > @@ -190,6 +190,20 @@ void kvmclock_cpu_action(enum kvm_guest_cpu_action a= ction) > =C2=A0 } > =C2=A0} > =C2=A0 > +static unsigned long kvm_get_cpu_khz(void) > +{ > + unsigned int cpu_khz; > + > + /* > + * Prefer CPUID over kvmclock when possible, as the base CPU frequency > + * isn't necessarily the same as the kvmlock "TSC" frequency. > + */ > + if (!cpuid_get_cpu_freq(&cpu_khz)) > + return cpu_khz; > + > + return pvclock_tsc_khz(this_cpu_pvti()); I'm fine with this in principle but shouldn't the fallback be calling kvm_get_tsc_khz() instead of directly calling pvclock_tsc_khz()? --=-iph/FD/9Oere6U4F6y6S Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCD9Aw ggSOMIIDdqADAgECAhAOmiw0ECVD4cWj5DqVrT9PMA0GCSqGSIb3DQEBCwUAMGUxCzAJBgNVBAYT AlVTMRUwEwYDVQQKEwxEaWdpQ2VydCBJbmMxGTAXBgNVBAsTEHd3dy5kaWdpY2VydC5jb20xJDAi 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