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 71856128395; Sun, 10 May 2026 21:05:56 +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=1778447158; cv=none; b=BtGNkgZQl/20qrTKm6g7tGPlpDDBL4xoRy6K4CkTPrB/PrjvpaSeZUxbWKX+t9R51Zev1dYoszvIxRdAudxFKI+K/pmuUEM8NIlvACgXeHv/DdsAOF40Hny2riVYdUUcHRu2SIUnBkbIENurQOv8WBbHvICxEPI2PtBzjGFuIiE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778447158; c=relaxed/simple; bh=fcCIydfNLNpAW8zQ9QSDkJT61um6BZZ49a8aN0wyqq4=; h=Message-ID:Subject:From:To:Date:In-Reply-To:References: Content-Type:MIME-Version; b=ESVgXGHMAjuwbrIOEaVzsVxO07SAPXk4ZnBKvaxLkt+uoZWOH3n+zQ03XK14Lm+r9GeY5Nor4vwK900geM439dLEdUnigxaM5lbqNan6eh+yRMrDcx1dcxpuAcPSXdk+JbyLV64JbhzWvOdE47ryBb+4LVS6I+ryAjMCsFzRbGg= 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=k3gDaT7v; 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="k3gDaT7v" 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:To:From:Subject:Message-ID:Sender:Reply-To:Cc: Content-Transfer-Encoding:Content-ID:Content-Description; bh=bhNOFvkH719t7i9pQvqgD9PQhJFs6ir/zUj3G3rKD18=; b=k3gDaT7vBcXRudpVf2JczbIT1q 5afuzuA0DX9RyNuKWPIbcFfMzM95N5bcyy38ZIevIkLL9zY4zLoghfyqt5mCgw8RfARtFladk4DRS mhEmCZR0wnj1sMkVgMRew2bzKtPMcrFIMBGzMRto5CiJui/yonAWitgBo7DXOG5JF9RIu1i377M2A pgfSLhdq3rJcC+kwSrgxUxqx9iVfay9FgtA+vIZz0+eZTBiF3uABfmOlRptJ3ez23N83pSvwwqWSb icd8XPttOeADBiZBrMnnQzrvU7QGpB/zx9+imXaF4rhTGXJghLDrx3sI7cbaAI/Qvr8bngLVEixRy 87Plb/WQ==; Received: from 54-240-197-234.amazon.com ([54.240.197.234] helo=u09cd745991455d.ant.amazon.com) by casper.infradead.org with esmtpsa (Exim 4.99.1 #2 (Red Hat Linux)) id 1wMBLA-00000007GmD-1vIF; Sun, 10 May 2026 21:05:36 +0000 Message-ID: <66458bbc44f98b7f9742007348a9f70ee8086429.camel@infradead.org> Subject: [PATCH v4 32/30] KVM: x86: Re-synchronize TSC after KVM_SET_TSC_KHZ From: David Woodhouse To: Paolo Bonzini , Jonathan Corbet , Shuah Khan , Sean Christopherson , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Vitaly Kuznetsov , Juergen Gross , Boris Ostrovsky , David Woodhouse , Paul Durrant , Jonathan Cameron , Sascha Bischoff , Marc Zyngier , Dongli Zhang , Jack Allister , Joe Jin , Joey Gouly , kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org, linux-kselftest@vger.kernel.org Date: Sun, 10 May 2026 22:05:31 +0100 In-Reply-To: <20260509224824.3264567-1-dwmw2@infradead.org> References: <20260509224824.3264567-1-dwmw2@infradead.org> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-n1rYoFphXBZk9zIVxw0J" User-Agent: Evolution 3.52.3-0ubuntu1.1 Precedence: bulk X-Mailing-List: linux-doc@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 --=-n1rYoFphXBZk9zIVxw0J Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable From: David Woodhouse KVM_SET_TSC_KHZ changes the vCPU's TSC scaling ratio but does not update the VM-wide cur_tsc_scaling_ratio used by get_kvmclock(). This causes get_kvmclock() to use a stale (default 1:1) ratio when computing the KVM clock, leading to drift between the host-side kvmclock and what the guest observes. Fix this by calling kvm_synchronize_tsc() after changing the TSC frequency. This: - Updates cur_tsc_scaling_ratio (consumed by pvclock_update_vm_gtod_copy) - Ensures the TSC value is continuous across the frequency change - Triggers kvm_track_tsc_matching() for proper masterclock handling - Allows subsequent vCPUs to synchronize via the 1-second slop hack Signed-off-by: David Woodhouse --- arch/x86/kvm/x86.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index ac982652e5e0..833a4f119e22 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -206,6 +206,7 @@ module_param(mitigate_smt_rsb, bool, 0444); #ifdef CONFIG_X86_64 static bool kvm_get_time_and_clockread(s64 *kernel_ns, u64 *tsc_timestamp)= ; #endif +static void kvm_synchronize_tsc(struct kvm_vcpu *vcpu, u64 *user_value); #define KVM_MAX_NR_USER_RETURN_MSRS 16 =20 struct kvm_user_return_msrs { @@ -2611,7 +2612,20 @@ static int kvm_set_tsc_khz(struct kvm_vcpu *vcpu, u3= 2 user_tsc_khz) user_tsc_khz, thresh_lo, thresh_hi); use_scaling =3D 1; } - return set_tsc_khz(vcpu, user_tsc_khz, use_scaling); + if (set_tsc_khz(vcpu, user_tsc_khz, use_scaling)) + return -1; + + /* + * Re-synchronize the TSC after changing frequency. This ensures + * cur_tsc_scaling_ratio is updated (used by get_kvmclock) and + * the TSC value is continuous across the frequency change. + */ + { + u64 tsc =3D kvm_read_l1_tsc(vcpu, rdtsc()); + + kvm_synchronize_tsc(vcpu, &tsc); + } + return 0; } =20 static s64 compute_guest_tsc(struct kvm_vcpu *vcpu, s64 kernel_ns) --=20 2.43.0 --=-n1rYoFphXBZk9zIVxw0J Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCD9Aw ggSOMIIDdqADAgECAhAOmiw0ECVD4cWj5DqVrT9PMA0GCSqGSIb3DQEBCwUAMGUxCzAJBgNVBAYT AlVTMRUwEwYDVQQKEwxEaWdpQ2VydCBJbmMxGTAXBgNVBAsTEHd3dy5kaWdpY2VydC5jb20xJDAi BgNVBAMTG0RpZ2lDZXJ0IEFzc3VyZWQgSUQgUm9vdCBDQTAeFw0yNDAxMzAwMDAwMDBaFw0zMTEx MDkyMzU5NTlaMEExCzAJBgNVBAYTAkFVMRAwDgYDVQQKEwdWZXJva2V5MSAwHgYDVQQDExdWZXJv a2V5IFNlY3VyZSBFbWFpbCBHMjCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAMjvgLKj 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