Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752458AbeAERst (ORCPT + 1 other); Fri, 5 Jan 2018 12:48:49 -0500 Received: from twosheds.infradead.org ([90.155.92.209]:53188 "EHLO twosheds.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752295AbeAERss (ORCPT ); Fri, 5 Jan 2018 12:48:48 -0500 Message-ID: <1515174510.29312.169.camel@infradead.org> Subject: Re: [PATCH v3 01/13] x86/retpoline: Add initial retpoline support From: David Woodhouse To: Linus Torvalds Cc: "bp@suse.de" , "linux-kernel@vger.kernel.org" , "peterz@infradead.org" , "tim.c.chen@linux.intel.com" , "tglx@linutronix.de" , "ak@linux.intel.com" , "riel@redhat.com" , "keescook@google.com" , "gnomes@lxorguk.ukuu.org.uk" , "pjt@google.com" , "dave.hansen@intel.com" , "luto@amacapital.net" , "jikos@kernel.org" , "gregkh@linux-foundation.org" In-Reply-To: References: <1515058213.12987.89.camel@amazon.co.uk> <20180104143710.8961-1-dwmw@amazon.co.uk> <1515160619.29312.126.camel@amazon.co.uk> <1515170506.29312.149.camel@amazon.co.uk> <20180105164505.xpw5pefxsyu3z56e@pd.tnic> <1515172353.29312.161.camel@amazon.co.uk> Face: 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 Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-rOHMdgT9YmHNYeRzOC1A" Date: Fri, 05 Jan 2018 17:48:30 +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: --=-rOHMdgT9YmHNYeRzOC1A Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Fri, 2018-01-05 at 09:28 -0800, Linus Torvalds wrote: >=20 > Yes, I would suggest against expecting altinstructions to have > relocation information. They are generated in a different place, so.. >=20 > That said, I honestly like the inline version (the one that is in the > google paper first) of the retpoline more than the out-of-line one. > And that one shouldn't have any relocagtion issues, because all the > offsets are relative. >=20 > We want to use that one for the entry stub anyway, can't we just > standardize on that one for all our assembly? Sure, that's just a case of tweaking the macros a little to do it inline instead of jumping to the thunk. I thunk judicious use of __stringify() has resolved any issues I might have had with that approach in the first place. However... > If the *compiler* uses the out-of-line version, that's a separate > thing. But for our asm cases, let's just make it all be the inline > case, ok? >=20 > It also should simplify the whole target generation. None of this > silly "__x86.indirect_thunk.\reg" crap with different targets for > different register choices. If we're going to let the compiler use the out-of-line version (which we *want* to because otherwise we don't get to ALTERNATIVE it away as appropriate), then we still need to emit the various __x86.indirect_thunk.\reg thunks for the compiler to use anyway. At that point, there isn't a *huge* benefit to doing the retpoline inline in our own asm, when it might as well just be a jump to the thunks which exist anyway. But neither do I have an argument *against* doing so, so I'll happily tweak the NOSPEC_CALL/NOSPEC_JMP macros accordingly if you really want... --=-rOHMdgT9YmHNYeRzOC1A 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 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