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 X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3E933C433DF for ; Wed, 20 May 2020 22:17:54 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 055B320829 for ; Wed, 20 May 2020 22:17:53 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 055B320829 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=citrix.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jbX1n-0000Wx-Jm; Wed, 20 May 2020 22:17:31 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jbX1m-0000Ws-D0 for xen-devel@lists.xenproject.org; Wed, 20 May 2020 22:17:30 +0000 X-Inumbo-ID: b168c048-9ae7-11ea-b9cf-bc764e2007e4 Received: from ppsw-30.csi.cam.ac.uk (unknown [131.111.8.130]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id b168c048-9ae7-11ea-b9cf-bc764e2007e4; Wed, 20 May 2020 22:17:29 +0000 (UTC) X-Cam-AntiVirus: no malware found X-Cam-ScannerInfo: http://help.uis.cam.ac.uk/email-scanner-virus Received: from 88-109-182-220.dynamic.dsl.as9105.com ([88.109.182.220]:53322 helo=[192.168.1.219]) by ppsw-30.csi.cam.ac.uk (smtp.hermes.cam.ac.uk [131.111.8.156]:465) with esmtpsa (PLAIN:amc96) (TLSv1.2:ECDHE-RSA-AES128-GCM-SHA256:128) id 1jbX1i-000Ef4-dM (Exim 4.92.3) (return-path ); Wed, 20 May 2020 23:17:26 +0100 Subject: Re: [PATCH v5] x86: clear RDRAND CPUID bit on AMD family 15h/16h To: Jan Beulich , "xen-devel@lists.xenproject.org" References: <4f76749b-54bd-7c39-6c90-279ce25cb57c@suse.com> From: Andrew Cooper Message-ID: Date: Wed, 20 May 2020 23:17:25 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <4f76749b-54bd-7c39-6c90-279ce25cb57c@suse.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Language: en-GB X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: Wei Liu , =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" On 18/05/2020 14:19, Jan Beulich wrote: > Inspired by Linux commit c49a0a80137c7ca7d6ced4c812c9e07a949f6f24: > > There have been reports of RDRAND issues after resuming from suspend on > some AMD family 15h and family 16h systems. This issue stems from a BIOS > not performing the proper steps during resume to ensure RDRAND continues > to function properly. > > Update the CPU initialization to clear the RDRAND CPUID bit for any family > 15h and 16h processor that supports RDRAND. If it is known that the family > 15h or family 16h system does not have an RDRAND resume issue or that the > system will not be placed in suspend, the "cpuid=rdrand" kernel parameter > can be used to stop the clearing of the RDRAND CPUID bit. > > Note, that clearing the RDRAND CPUID bit does not prevent a processor > that normally supports the RDRAND instruction from executing it. So any > code that determined the support based on family and model won't #UD. > > Warn if no explicit choice was given on affected hardware. > > Check RDRAND functions at boot as well as after S3 resume (the retry > limit chosen is entirely arbitrary). > > Signed-off-by: Jan Beulich > Reviewed-by: Roger Pau Monné Acked-by: Andrew Cooper > --- > Still slightly RFC, and still in particular because of the change to > parse_xen_cpuid(): Alternative approach suggestions are welcome. But now > also because with many CPUs there may now be a lot of warnings in case > of issues. It would still be nice if we could find a better way of determining whether S3 is supported on the platform, which would at least let us sort server and client platforms. A straight string search for _S3 in the DSDT does look to be effective, on a sample of 5 boxes I've tried. ~Andrew