From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: ACJfBov55ZxB6bhiIiyNbYIc9SioTES0QxkDroGo6Bw86H705plkKqoTB4AlReIUsffBuIpk1o9d ARC-Seal: i=1; a=rsa-sha256; t=1515449946; cv=none; d=google.com; s=arc-20160816; b=XUZRPoFgVlqSsjQRXOrzmfkvwdisbboLzPKD5XIv0ch8sRLvB+AIDcdXuYNEXA2wtv pNhIFbg08pfH4G0XpAeZD7E2qZFZSSoFt7fbUT9BT0GqyBAnay1FciHW4B7TYQMuYvyQ pZ7UHEWopapPyP5MajECB0S11sfRXrSCLy/xsxJNcBaYRhfIDDzsY/RWeHf952BATxd8 rBGTIcvCU/buop+8F6H+mfZMJ12b5cJLOTxiuq9PqohHfSkLjoJwScxJiW12Zstkr5+U rR68ByVIGiZLBLwHXpCLcftvRgAjFclpH3sH+p3iTjn/vHlYVs30SBVyQxVLy1tMQrMs sW3w== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=precedence:mime-version:accept-language:in-reply-to:references :message-id:date:thread-index:thread-topic:subject:cc:to:from :mime-version:dkim-signature:arc-authentication-results; bh=2RjL9JcRcUh7JHIbiD4MkTh/Z9rvdSGrN5xnouY/6+k=; b=Cm8rdhKAYuAsHvu6BQHfV86ZntZQi6gLn5e3miWxBdx59SVa/M84xeJhXdq4NABcng 2PYTPX8q5CuvwgKXrrqhu2x+4EAedsgCagwx60NFKIthNh8xMryO7kTQwZoWKKBz0PVq BC3hvs4R5+6kSqmut5/m01Y+v4mZq52fK32xGVOhim0hpL+7eqJa1fQZAXA37AIeKc8W tCg2JiogPmGT/Rn09VWpAGKzTLKwfl01vuhaK4P3csefkMDdJP0INE/UBy539qlz0F6+ wdPuNOlzUmRWJ0XoB+7wXsvneCKIlT1juMJDMMhcxb0GtiBG7CPiw2cJ/rWDCOC4jc2e 3tGQ== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@amazon.co.uk header.s=amazon201209 header.b=cHFrfJ8C; spf=pass (google.com: domain of prvs=539e5dcb6=dwmw@amazon.co.uk designates 207.171.184.29 as permitted sender) smtp.mailfrom=prvs=539e5dcb6=dwmw@amazon.co.uk; dmarc=pass (p=QUARANTINE sp=QUARANTINE dis=NONE) header.from=amazon.co.uk Authentication-Results: mx.google.com; dkim=pass header.i=@amazon.co.uk header.s=amazon201209 header.b=cHFrfJ8C; spf=pass (google.com: domain of prvs=539e5dcb6=dwmw@amazon.co.uk designates 207.171.184.29 as permitted sender) smtp.mailfrom=prvs=539e5dcb6=dwmw@amazon.co.uk; dmarc=pass (p=QUARANTINE sp=QUARANTINE dis=NONE) header.from=amazon.co.uk X-Amazon-filename: smime.p7s X-IronPort-AV: E=Sophos;i="5.46,332,1511827200"; d="p7s'?scan'208";a="584988596" Content-Type: multipart/mixed; boundary="===============2894579398333474129==" MIME-Version: 1.0 From: "Woodhouse, David" To: "peterz@infradead.org" , "andi@firstfloor.org" CC: "linux-kernel@vger.kernel.org" , "tim.c.chen@linux.intel.com" , "tglx@linutronix.de" , "ak@linux.intel.com" , "pjt@google.com" , "dave.hansen@intel.com" , "luto@amacapital.net" , "gregkh@linux-foundation.org" Subject: Re: [PATCH] x86/retpoline: Avoid return buffer underflows on context switch Thread-Topic: [PATCH] x86/retpoline: Avoid return buffer underflows on context switch Thread-Index: AQHTiMfVdOWxn93ytEiH0Qj57uVnLKNqiaqAgAABq4A= Date: Mon, 8 Jan 2018 22:17:19 +0000 Message-ID: <1515449839.4423.37.camel@amazon.co.uk> References: <20180108201531.6782-1-andi@firstfloor.org> <20180108221121.GU29822@worktop.programming.kicks-ass.net> In-Reply-To: <20180108221121.GU29822@worktop.programming.kicks-ass.net> Accept-Language: en-GB, en-US X-MS-Has-Attach: yes X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.43.60.176] MIME-Version: 1.0 X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1589061348548787060?= X-GMAIL-MSGID: =?utf-8?q?1589064443653836253?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: --===============2894579398333474129== Content-Language: en-US Content-Type: multipart/signed; micalg=sha-256; protocol="application/x-pkcs7-signature"; boundary="=-ao1J52DUMawWrZu36Gra" --=-ao1J52DUMawWrZu36Gra Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Mon, 2018-01-08 at 23:11 +0100, Peter Zijlstra wrote: >=20 > So pjt did alignment, a single unroll and per discussion earlier today > (CET) or late last night (PST), he only does 16. Hey Intel, please tell us precisely how many RSB entries there are, on each family of CPU... :) > Why is none of that done here? Also, can we pretty please stop using > those retarded number labels, they make this stuff unreadable. >=20 > Also, pause is unlikely to stop speculation, that comment doesn't make > sense. Looking at PJT's version there used to be a speculation trap in > there, but I can't see that here. In this particular code we don't need a speculation trap; that's elsewhere. This one is *just* about the call stack. And the reason we don't just have... =C2=A0call . + 5 =C2=A0call . + 5 =C2=A0call . + 5 =C2=A0... is because that might get interpreted as a "push %rip" and not go on the RSB at all. 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