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: Fri, 16 Feb 2018 09:58:56 +0000 Message-ID: <1518775136.7876.13.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> <1518509708.12890.33.camel@infradead.org> <27c85759-e662-d281-f8a0-0a80ca8ee18f@redhat.com> <1518517262.12890.43.camel@infradead.org> <1518518198.12890.48.camel@infradead.org> <02bd3fdd-1b73-6cab-fb09-38ba933396bd@redhat.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-kcJPPKNcZ2jH/8PnJRXN" Cc: Ingo Molnar 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: <02bd3fdd-1b73-6cab-fb09-38ba933396bd@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org --=-kcJPPKNcZ2jH/8PnJRXN Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Tue, 2018-02-13 at 11:41 +0100, Paolo Bonzini wrote: > On 13/02/2018 11:36, David Woodhouse wrote: > > > > - if the VM has IBRS_ALL, pass through the MSR when it is zero and > > > > intercept writes when it is one (no writes should happen) > > > > =C2=A0 > > > > - if the VM doesn't have IBRS_ALL, do as we are doing now, independ= ent > > > > of what the host spectre_v2_ibrs_all() setting is. > > > > > > We end up having to turn IBRS on again on vmexit then, taking care th= at > > > no conditional branch can go round it. So that becomes an > > > *unconditional* wrmsr or lfence in the vmexit path. We really don't > > > want that. > > > > > Note that being able to keep it simple in KVM was basically what made > > the difference between me tolerating IBRS_ALL as Intel currently define > > it, and throwing my toys out of the pram (as I had done in the first > > iterations of this patch). >=C2=A0 > You have my vote. :)=C2=A0 I was taking that as assent to the patch... could I trouble you for an explicit ack, please? --=-kcJPPKNcZ2jH/8PnJRXN 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 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