From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <1518006004.3677.115.camel@infradead.org> Subject: Re: [PATCH 6/6] s390: introduce execute-trampolines for branches From: David Woodhouse In-Reply-To: <20180207131719.4aeb316e@mschwideX1> References: <1517986811-27819-1-git-send-email-schwidefsky@de.ibm.com> <1517986811-27819-7-git-send-email-schwidefsky@de.ibm.com> <20180207100726.GB31392@amd> <1518005275.3677.112.camel@infradead.org> <20180207131719.4aeb316e@mschwideX1> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-rT0xjnV9L/P+V12cmKvK" Date: Wed, 07 Feb 2018 12:20:04 +0000 Mime-Version: 1.0 List-Archive: List-Post: To: Martin Schwidefsky , Linus Torvalds Cc: Pavel Machek , linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, Heiko Carstens , Christian Borntraeger , Cornelia Huck , David Hildenbrand , Greg Kroah-Hartman , Jon Masters , Marcus Meissner , Jiri Kosina , Dominik Brodowski , Alan Cox List-ID: --=-rT0xjnV9L/P+V12cmKvK Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, 2018-02-07 at 13:17 +0100, Martin Schwidefsky wrote: > On Wed, 07 Feb 2018 12:07:55 +0000 > David Woodhouse wrote: >=20 > >=20 > > On Wed, 2018-02-07 at 11:07 +0100, Pavel Machek wrote: > > >=20 > > > This is really unfortunate naming of kernel option. > > >=20 > > > spectre_v2=3Doff sounds like we are turning the "bug" off, but i some= how > > > suspect you are turning the bug _workaround_ off.=C2=A0=C2=A0 > > That's consistent with what we have on x86. > >=20 > > >=20 > > > >=20 > > > > +ifdef CONFIG_EXPOLINE > > > > +=C2=A0=C2=A0ifeq ($(call cc-option-yn,$(CC_FLAGS_MARCH) -mindirect= -branch=3Dthunk),y) > > > > +=C2=A0=C2=A0=C2=A0=C2=A0CC_FLAGS_EXPOLINE :=3D -mindirect-branch= =3Dthunk > > > > +=C2=A0=C2=A0=C2=A0=C2=A0CC_FLAGS_EXPOLINE +=3D -mfunction-return= =3Dthunk > > > > +=C2=A0=C2=A0=C2=A0=C2=A0CC_FLAGS_EXPOLINE +=3D -mindirect-branch-t= able > > > > +=C2=A0=C2=A0=C2=A0=C2=A0export CC_FLAGS_EXPOLINE > > > > +=C2=A0=C2=A0=C2=A0=C2=A0cflags-y +=3D $(CC_FLAGS_EXPOLINE) > > > > +=C2=A0=C2=A0else > > > > +=C2=A0=C2=A0=C2=A0=C2=A0$(warning "Your gcc lacks the -mindirect-b= ranch=3D option") > > > > +=C2=A0=C2=A0endif > > > > +endif=C2=A0=C2=A0 > > That isn't, though. Linus asked us to drop the $(warning) part. > >=20 > > ... and then spent a week building with a non-retpoline compiler and > > not noticing, so he might have changed his mind ;) > > I found the warning to have some value, it helps for the case where my > fingers are faster than my brain and I type "make" instead of "smake" > which uses the alternative compiler with the required support. >=20 > @Linus: do you want a warning or prefer not to have one ? FWIW I agreed to drop it when the plan in my head was "we'll just turn on IBRS instead if the compiler doesn't do full retpoline support". Now that Linus has expressed a disinclination to take IBRS support in that form, I might be more inclined to defend the $(warning) too. --=-rT0xjnV9L/P+V12cmKvK 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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