From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Woodhouse Subject: Re: [RFC 09/10] x86/enter: Create macros to restrict/unrestrict Indirect Branch Speculation Date: Tue, 23 Jan 2018 10:27:24 +0000 Message-ID: <1516703244.9521.132.camel@infradead.org> References: <1516476182-5153-10-git-send-email-karahmed@amazon.de> <1516566497.9814.78.camel@infradead.org> <1516572013.9814.109.camel@infradead.org> <1516638426.9521.20.camel@infradead.org> <20180123072930.soz25cyky3u4hpgv@gmail.com> <20180123075358.nztpyxympwfkyi2a@gmail.com> <1516699832.9521.123.camel@infradead.org> <20180123101532.obioudsu3ecm4rez@gmail.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-6QNJZQ4wzgySCtvfcMaV" Cc: Linus Torvalds , KarimAllah Ahmed , Linux Kernel Mailing List , Andi Kleen , Andrea Arcangeli , Andy Lutomirski , Arjan van de Ven , Ashok Raj , Asit Mallick , Borislav Petkov , Dan Williams , Dave Hansen , Greg Kroah-Hartman , "H . Peter Anvin" , Ingo Molnar , Janakarajan Natarajan , Joerg Roedel , Jun Nakajima , Laura Abbott , To: Ingo Molnar Return-path: In-Reply-To: <20180123101532.obioudsu3ecm4rez@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org --=-6QNJZQ4wzgySCtvfcMaV Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Tue, 2018-01-23 at 11:15 +0100, Ingo Molnar wrote: >=20 > BTW., the reason this is enabled on all distro kernels is because the ove= rhead is=C2=A0 > a single patched-in NOP instruction in the function epilogue, when tracin= g is=C2=A0 > disabled. So it's not even a CALL+RET - it's a patched in NOP. Hm? We still have GCC emitting 'call __fentry__' don't we? Would be nice to get to the point where we can patch *that* out into a NOP... or are you saying we already can? But this is a digression. I was being pedantic about the "0 cycles" but sure, this would be perfectly tolerable. --=-6QNJZQ4wzgySCtvfcMaV 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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