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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 35682C38A2A for ; Fri, 8 May 2020 13:59:22 +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 0E592208CA for ; Fri, 8 May 2020 13:59:21 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0E592208CA Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.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 1jX3Wr-0001GE-0z; Fri, 08 May 2020 13:59:05 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jX3Wp-0001G9-Tu for xen-devel@lists.xenproject.org; Fri, 08 May 2020 13:59:03 +0000 X-Inumbo-ID: 12e73f42-9134-11ea-b9cf-bc764e2007e4 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id 12e73f42-9134-11ea-b9cf-bc764e2007e4; Fri, 08 May 2020 13:59:03 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id EFE5CABC7; Fri, 8 May 2020 13:59:04 +0000 (UTC) Subject: Re: [PATCH v8 04/12] x86emul: support SERIALIZE To: Andrew Cooper References: <60cc730f-2a1c-d7a6-74fe-64f3c9308831@suse.com> <0bbbf95e-48ec-ee73-5234-52cf9c6c06d8@suse.com> <64de91ff-41ae-baf1-1119-0ba39df32275@citrix.com> <0c5a03c6-6c4f-c6ec-e474-71a2badd1c9c@suse.com> From: Jan Beulich Message-ID: <1a4a9298-3446-a863-2e24-4c81244594dd@suse.com> Date: Fri, 8 May 2020 15:59:01 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit 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: "xen-devel@lists.xenproject.org" , Wei Liu , Roger Pau Monne Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" On 08.05.2020 15:00, Andrew Cooper wrote: > On 08/05/2020 08:34, Jan Beulich wrote: >>>> @@ -5660,6 +5661,18 @@ x86_emulate( >>>> goto done; >>>> break; >>>> >>>> + case 0xe8: >>>> + switch ( vex.pfx ) >>>> + { >>>> + case vex_none: /* serialize */ >>>> + host_and_vcpu_must_have(serialize); >>>> + asm volatile ( ".byte 0x0f, 0x01, 0xe8" ); >>> There is very little need for an actual implementation here.  The VMExit >>> to get here is good enough. >>> >>> The only question is whether pre-unrestricted_guest Intel boxes are >>> liable to find this in real mode code. >> Apart from this we also shouldn't assume HVM in the core emulator, >> I think. > > It's not assuming HVM.  Its just that there is no way we can end up > emulating this instruction from PV context. > > If we could end up here in PV context, the exception causing us to > emulate to begin with would be good enough as well. With the current way of where/how emulation gets involved - yes. I'd like to remind you though of the 4-insn window shadow code tries to emulate over for PAE guests. There is no intervening #VMEXIT there. So do you want me to drop the asm() then, and switch from host_and_vcpu_must_have(serialize) to just vcpu_must_have(serialize)? Jan