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 EA046263F32; Fri, 29 Aug 2025 11:20:04 +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=1756466407; cv=none; b=b0Eiogv9xhPzzt4gKN4wzsojKzpELi3jZ5gNTgfAS9IB+e1MTsgbcQusfVTduU6JlAUvFkXpXELigaGFetyYfVcg8VV1oYi6booGgxqIRQJ0ivYpfoUmeLsqo8pGkZHCRS49QvXxJQx8SryA05JQ2PrPv4gSRdSocP1DeElbzWI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756466407; c=relaxed/simple; bh=IioMTMZQJQtqp5e9OUPbFXmKxVgnVdVkwhMa/QyEbxs=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=QjN/6JXFsbjRh3RAALE46YJuGEITxcyelRcC3SkdXaJgJvp9chHt4NNwcnqP3wvXHotW/6xpohnJwbJL1iTQlzWZ4TWA4Y8fb9MtcKmEaAd0gk/JF0bXPnBvYd3eN87Nkjf5yMNhOB36OcHPeb/CFIq3pGQqAO9Ye6WeTr5mWi4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (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=O1+QZq5W; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (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="O1+QZq5W" 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=IioMTMZQJQtqp5e9OUPbFXmKxVgnVdVkwhMa/QyEbxs=; b=O1+QZq5WpX4gPELsLhug0lgwOk S792j5Xwqu2qO96h1az7tJFPw/q3aKVb91fYdwsAJDbbP+1dEPjK0kD6CXSRSNLzfOBGoimzlmyqN zUx4Tvj9dcwH/PL8qddiKNeDsE1ePm+3c3PwfuEuPNMMxAvE0a+1mFkw4Q7MVl0uuTdNiBnrCPUC4 yM2ooJTRAHwCaRhpCaB5KeLuuL/54P3viJ/gfhqNFhcmLkykOHuXpmo+TmNaAlvDbahlXlf0SGc3+ aBPM347xZFfXjdAwau8i7uatcSsOxMI+eiOxVi1sDVzlvlmzhPT/0AkQPYtHF4afCdqN/OzB/M27A FrMmQAJg==; Received: from 54-240-197-239.amazon.com ([54.240.197.239] helo=u09cd745991455d.ant.amazon.com) by casper.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1urx97-0000000AbP1-3CKw; Fri, 29 Aug 2025 11:19:54 +0000 Message-ID: Subject: Re: [PATCH v2 0/3] Support "generic" CPUID timing leaf as KVM guest and host From: David Woodhouse To: "Durrant, Paul" , Sean Christopherson , "Griffoul, Fred" Cc: Colin Percival , Paolo Bonzini , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "x86@kernel.org" , "H. Peter Anvin" , Vitaly Kuznetsov , "kvm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "Graf (AWS), Alexander" , Ajay Kaher , Alexey Makhalov Date: Fri, 29 Aug 2025 12:19:53 +0100 In-Reply-To: <54BCC060-1C9B-4BE4-8057-0161E816A9A3@amazon.co.uk> References: <20250816101308.2594298-1-dwmw2@infradead.org> <933dc95ead067cf1b362f7b8c3ce9a72e31658d2.camel@infradead.org> <6783241f1bfadad8429f66c82a2f8810a74285a0.camel@infradead.org> <01000198cf7ec03e-dfc78632-42ee-480b-8b51-3446fbb555d1-000000@email.amazonses.com> <54BCC060-1C9B-4BE4-8057-0161E816A9A3@amazon.co.uk> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-Wy4hrKJuq7zEuBbhX7n/" User-Agent: Evolution 3.52.3-0ubuntu1 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org 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 --=-Wy4hrKJuq7zEuBbhX7n/ Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Fri, 2025-08-29 at 11:08 +0000, Durrant, Paul wrote: > On 29/08/2025, 10:51, "David Woodhouse" > wrote: > [snip] > > =E2=80=A2 Declare that we don't care that it's strictly an ABI change, = and > > VMMs which used to just populate the leaf and let KVM fill it in > > for Xen guests now *have* to use the new API. > >=20 > >=20 > > I'm actually OK with that, even the last one, because I've just noticed > > that KVM is updating the *wrong* Xen leaf. 0x40000x03/2 EAX is supposed > > to be the *host* TSC frequency, and the guest frequency is supposed to > > be in 0x40000x03/0 ECX. And Linux as a Xen guest doesn't even use it > > anyway, AFAICT > >=20 > > Paul, it was your code originally; are you happy with removing it? >=20 > Yes, if it is incorrect then please fix it. I must have become > confused whilst reading the original Xen code.=20 The proposal is not to *fix* it but just to rip it out entirely and provide userspace with some way of knowing the effective TSC frequency. This does mean userspace would have to set the vCPU's TSC frequency and then query the kernel before setting up its CPUID. And in the absence of scaling, this KVM API would report the hardware TSC frequency. I guess the API would have to return -EHARDWARETOOSTUPID if the TSC frequency *isn't* the same across all CPUs and all power states, etc. --=-Wy4hrKJuq7zEuBbhX7n/ 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 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