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 D54C8C43334 for ; Mon, 18 Jul 2022 08:19:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233815AbiGRITL (ORCPT ); Mon, 18 Jul 2022 04:19:11 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58916 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233771AbiGRITE (ORCPT ); Mon, 18 Jul 2022 04:19:04 -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 4CD56B849 for ; Mon, 18 Jul 2022 01:19:03 -0700 (PDT) Received: from [212.54.57.108] (helo=csmtp4.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 1oDLy2-0005F5-06 for linux-kernel@vger.kernel.org; Mon, 18 Jul 2022 10:19:02 +0200 Received: from llamedos.mydomain ([81.97.236.130]) by cmsmtp with ESMTPA id DLy1opNWRuYlrDLy1oRSOL; Mon, 18 Jul 2022 10:19:01 +0200 X-SourceIP: 81.97.236.130 X-Authenticated-Sender: zarniwhoop@ntlworld.com X-Spam: 0 X-Authority: v=2.4 cv=RoXWkQqK c=1 sm=1 tr=0 ts=62d51775 cx=a_exe a=OGiDJHazYrvzwCbh7ZIPzQ==:117 a=OGiDJHazYrvzwCbh7ZIPzQ==:17 a=IkcTkHD0fZMA:10 a=RgO8CyIxsXoA:10 a=zd2uoN0lAAAA:8 a=GQgagVcjBMtnFRtF3loA:9 a=QEXdDO2ut3YA:10 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ntlworld.com; s=meg.feb2017; t=1658132341; bh=V/C/Yeyoys4o7TehoWP926lx5yRUap6C1609FFWebys=; h=Date:From:To:Subject; b=ayAh9nwgdvHBrFI2O1lMC0SOwn6F7sssbd3po5CaREv8eKmPuwfPDxGr8+mIVtbsU 3i6wPRiFY0fXNPuizpu2rMah9nkOgl6FzwLFEhTVoQpffX/Va7ip4/N1x6NLHDvbY4 HJk9KgzTiRoiHUFZNHeFsY7ybVEcfPMRwez3kddG59/RlN8zZWhyuiAEfSZ1Ub3szU lMqqiFmuzmrtLZ202oOe0YP2DHwQOoN/0ZCiItcQgqlBPCzpkb0kHho4GKfZKsXyzG Z4Ff6DMljuyPFNX62qEo3iay57fgYXKUtRT66Qjo/g2sb3Iq7paEz96wKua6Stkm5F YeAXjbz8zYrDQ== Received: by llamedos.mydomain (Postfix, from userid 1000) id 9E99A8DB5C; Mon, 18 Jul 2022 09:19:01 +0100 (BST) Date: Mon, 18 Jul 2022 09:19:01 +0100 From: Ken Moffat To: linux-kernel@vger.kernel.org Subject: Retbleed, Zen2 and STIBP Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Clacks-Overhead: GNU Terry Pratchett Content-Transfer-Encoding: 8bit User-Agent: Mutt/2.2.6 (2022-06-05) X-CMAE-Envelope: MS4xfFOLku9WgYEKmdRdm/nvrbE3/D3Bjzf4qmp/FnBsB+7V4z4de2bxFPo3SKLY3eahoww5E/zhi7TZVvbqGdVXb5m+wia/5hf51D0hiYA/myNgh17OOnP2 gC9yyAqB/K51ojf2jhBa9cljxoFmBw9K4ACvDlOSNbg4NSExn94wFvSWlV1cMIawr3vI/HZR0ZOfc9Kfr7SNhy2nFm8FFcvTMP8= Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Probably like most people, I find the detail of the available retbleed mitigations obscure. In particular, for zen2 the options *might* include ibpb or unret. But I have failed to find what 'unret' actually means. Any pointers, please ? 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. Assuming, for the moment, that I might want to try this full mitigation, is there any way to set this in the absence of newer microcode ? Or should I just accept that the best I can get is 'unret', whatever that means ? 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