Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751950AbeAEPit (ORCPT + 1 other); Fri, 5 Jan 2018 10:38:49 -0500 Received: from twosheds.infradead.org ([90.155.92.209]:42924 "EHLO twosheds.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751514AbeAEPis (ORCPT ); Fri, 5 Jan 2018 10:38:48 -0500 Message-ID: <1515166704.29312.140.camel@infradead.org> Subject: Re: [PATCH 0/7] IBRS patch series From: David Woodhouse To: "Van De Ven, Arjan" , Paul Turner , Linus Torvalds Cc: Tim Chen , Thomas Gleixner , Andy Lutomirski , Greg KH , "Hansen, Dave" , Andrea Arcangeli , Andi Kleen , Linux Kernel Mailing List In-Reply-To: <0575AF4FD06DD142AD198903C74E1CC87A56B309@ORSMSX103.amr.corp.intel.com> References: <1515093549.29312.11.camel@infradead.org> <1515162514.29312.131.camel@infradead.org> <0575AF4FD06DD142AD198903C74E1CC87A56B309@ORSMSX103.amr.corp.intel.com> Face: 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 Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-Ag/CGvHhViJTddlUBt0j" Date: Fri, 05 Jan 2018 15:38:24 +0000 Mime-Version: 1.0 X-Mailer: Evolution 3.18.5.2-0ubuntu3.2 X-SRS-Rewrite: SMTP reverse-path rewritten from by twosheds.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: --=-Ag/CGvHhViJTddlUBt0j Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Fri, 2018-01-05 at 14:42 +0000, Van De Ven, Arjan wrote: > This is why I said I would like to see retpoline be the default, with > IBRS an opt-in for the paranoid. I guess David will turn that on ;-) I can live with that. It really depends how you look at it. We had IBRS first, and especially on Broadwell and earlier, its performance really is painful. Then came retpoline, purely as an optimisation. A very *important* performance improvement, but an optimisation nonetheless. When looking at optimisations, it is rare for us to say "oh, well it opens up only a *small* theoretical security hole, but it's faster so that's OK". Retpoline is sufficient on pre-Skylake. On Skylake... it's complicated, and that's why my default position has always been that we should prefer IBRS there. Especially as it isn't *even* as much of a performance win there. But you're right, the holes that it opens up when compared to IBRS are minimal, and it *is* still a performance win (just less so than on earlier CPUs). So if your recommendation is that we stick with retpoline until IBRS_ATT comes along, I can live with that. People always have the option to build without retpoline, and then they get to use IBRS in the kernel if they want. --=-Ag/CGvHhViJTddlUBt0j 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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