From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Woodhouse Subject: Re: [PATCH 2/2] x86/speculation: Support "Enhanced IBRS" on future CPUs Date: Tue, 13 Feb 2018 08:15:08 +0000 Message-ID: <1518509708.12890.33.camel@infradead.org> References: <1518449255-2182-1-git-send-email-dwmw@amazon.co.uk> <1518449255-2182-2-git-send-email-dwmw@amazon.co.uk> <7e2e5ad1-49b6-1fdb-4a62-8ad6aefc30a0@redhat.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-pBfZP5dAR9cB2AdA5O+1" To: Paolo Bonzini , tglx@linutronix.de, x86@kernel.org, kvm@vger.kernel.org, torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, arjan.van.de.ven@intel.com, dave.hansen@intel.com Return-path: In-Reply-To: <7e2e5ad1-49b6-1fdb-4a62-8ad6aefc30a0@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org --=-pBfZP5dAR9cB2AdA5O+1 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Tue, 2018-02-13 at 09:02 +0100, Paolo Bonzini wrote: > > --- a/arch/x86/kvm/vmx.c > > +++ b/arch/x86/kvm/vmx.c > > @@ -3419,13 +3419,14 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, s= truct msr_data *msr_info) > > =C2=A0 > > =C2=A0 vmx->spec_ctrl =3D data; > > =C2=A0 > > - if (!data) > > + if (!data && !spectre_v2_ibrs_all()) > > =C2=A0 break; > This should check the value of IBRS_ALL in the VM, not in the host. No, it's host we want. If IBRS_ALL is set in the host, we set the actual hardware MSR once at boot time and never touch it again. The SPEC_CTRL MSR we expose to guests is purely a no-op fiction. If spectre_v2_ibrs_all() is true then KVM should *never* actually pass through or touch the real MSR. --=-pBfZP5dAR9cB2AdA5O+1 Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCEFQw ggUxMIIEGaADAgECAhBNRhEyk/HZ7naOeTHWrzuAMA0GCSqGSIb3DQEBCwUAMIGXMQswCQYDVQQG EwJHQjEbMBkGA1UECBMSR3JlYXRlciBNYW5jaGVzdGVyMRAwDgYDVQQHEwdTYWxmb3JkMRowGAYD VQQKExFDT01PRE8gQ0EgTGltaXRlZDE9MDsGA1UEAxM0Q09NT0RPIFJTQSBDbGllbnQgQXV0aGVu dGljYXRpb24gYW5kIFNlY3VyZSBFbWFpbCBDQTAeFw0xNzEyMjEwMDAwMDBaFw0xODEyMjEyMzU5 NTlaMCQxIjAgBgkqhkiG9w0BCQEWE2R3bXcyQGluZnJhZGVhZC5vcmcwggEiMA0GCSqGSIb3DQEB AQUAA4IBDwAwggEKAoIBAQDgzLNWa18DNpGUj/ZeH0Sgz53ESIbzdPw3OJeuNP6jZhxZojbyfxbM hETscxI/Hj6UZ4a7sHm5BkVjlsB1Af2Za/PXUt8MmLAcPMHkMPGunvkUibEvblDvpqMkQZlaZM+t 5PqFmWkbehLaEvbpNY7dmEAAeKh4klTzJzrr5AAzaCQ32cA2e3+DEIv5O5l9ViMIjy/JM+xMQrfX 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