From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6FD5AC43334 for ; Mon, 18 Jul 2022 22:17:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234536AbiGRWRX (ORCPT ); Mon, 18 Jul 2022 18:17:23 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59054 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232115AbiGRWRU (ORCPT ); Mon, 18 Jul 2022 18:17:20 -0400 Received: from smtpq2.tb.ukmail.iss.as9143.net (smtpq2.tb.ukmail.iss.as9143.net [212.54.57.97]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9F6B92CDE2 for ; Mon, 18 Jul 2022 15:17:19 -0700 (PDT) Received: from [212.54.57.107] (helo=csmtp3.tb.ukmail.iss.as9143.net) by smtpq2.tb.ukmail.iss.as9143.net with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oDZ3F-0004Sq-V8 for linux-kernel@vger.kernel.org; Tue, 19 Jul 2022 00:17:17 +0200 Received: from llamedos.mydomain ([81.97.236.130]) by cmsmtp with ESMTPA id DZ3FoPKOj45FHDZ3FoyRHC; Tue, 19 Jul 2022 00:17:17 +0200 X-SourceIP: 81.97.236.130 X-Authenticated-Sender: zarniwhoop@ntlworld.com X-Spam: 0 X-Authority: v=2.4 cv=e64V9Il/ c=1 sm=1 tr=0 ts=62d5dbed cx=a_exe a=OGiDJHazYrvzwCbh7ZIPzQ==:117 a=OGiDJHazYrvzwCbh7ZIPzQ==:17 a=IkcTkHD0fZMA:10 a=RgO8CyIxsXoA:10 a=zd2uoN0lAAAA:8 a=AqaP6XfnJfmMz2SymAQA:9 a=QEXdDO2ut3YA:10 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ntlworld.com; s=meg.feb2017; t=1658182637; bh=hCnMqaD5w6X4h1smVOeulyXHGnrQ3edjw87XVqMWrx8=; h=Date:From:To:Subject:References:In-Reply-To; b=3JlOvd4We8l/HmB31t2Jm28fnrHB7sHrqRlH9wdmQVOvSDK2DS5IjsehjN4ok6QnZ Mx2BJx8MuvrNCI/3lgcFiS4fsJ+Z6LJ0eCBqyRg3u/RL1IVMGveB98XeZXmPeYz0pb RECeaFAfTHIfjM0xCReoKdiDXvIrFfVc8vVP1Od23qupCI1m9wLRb0gR/w1EeGGLmM Px1ESs2OKY+VMVYA2+hikr23W2+Do7hqrkTGb9vVYxvJ1qcj7n7bIAtRYYHbCYEWP8 r9iDLnkH4QgMqG27IZ90OUO4BS0M351y/9Dn3TGvEjOiRLDmEWj9lEK4F8ZgecrsJF cF+BVETIaqwdw== Received: by llamedos.mydomain (Postfix, from userid 1000) id 93E9A8DB5C; Mon, 18 Jul 2022 23:17:17 +0100 (BST) Date: Mon, 18 Jul 2022 23:17:17 +0100 From: Ken Moffat To: linux-kernel@vger.kernel.org Subject: Re: Retbleed, Zen2 and STIBP Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Clacks-Overhead: GNU Terry Pratchett Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/2.2.6 (2022-06-05) X-CMAE-Envelope: MS4xfHcZL6CKDZHFu/rOSnTEFhABp9eoNf+HOyH0N1xNAoWQHP7jjVOqcOUzpCpBdneUNur+3zFiu5kv7grf5HYCmzgUkVpE6hDhEHw2obZrE4U+Xu9MOGx8 Zi3+HdmiDWRCuQh2MN+lkA7ZdG2K+I4RQLu4kWrpH55tBKuvmlJKrY5FoweiQvA+PkBzr6X1MLkGigcybxbp7HVx8apr+yI3s10= Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 18, 2022 at 09:19:01AM +0100, Ken Moffat wrote: Replying to myself to close this speculative misunderstanding. > > While ibpb might be available (and slow), on my Renoir with > microcode level (0860106h) there were no newer microcode versions > available when I last looked (a few weeks ago) but note 7 at the > bottom of > https://www.amd.com/system/files/documents/technical-guidance-for-mitigating-branch-type-confusion_v > 7_20220712.pdf > implies that the relevant bit is only set on Renoir in 0860109h and > later. > > Some of the text in that pdf implies that at least one of the > options could be set if not already set from the microcode, but the > amount of detail leaves me totally lost. > Now that I've tried the options, I can see that ibpb *is* available on this zen2 desktop machine (and no, I have no desire to use it, having seen how much things slow down). The default (auto) on this zen2 is the same as 'unret', i.e. Mitigation: untrained return thunk; SMT enabled with STIBP protection ĸen -- It is very easy to get ridiculously confused about the tenses of time travel, but most things can be resolved by a sufficiently large ego. -- The Last Continent