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=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 1469AECE58D for ; Wed, 9 Oct 2019 12:34:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EBF25206C0 for ; Wed, 9 Oct 2019 12:34:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730979AbfJIMeX (ORCPT ); Wed, 9 Oct 2019 08:34:23 -0400 Received: from mx1.redhat.com ([209.132.183.28]:31866 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730244AbfJIMeW (ORCPT ); Wed, 9 Oct 2019 08:34:22 -0400 Received: from mail-wm1-f70.google.com (mail-wm1-f70.google.com [209.85.128.70]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 7E0483CBE2 for ; Wed, 9 Oct 2019 12:34:22 +0000 (UTC) Received: by mail-wm1-f70.google.com with SMTP id p6so442846wmc.3 for ; Wed, 09 Oct 2019 05:34:22 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:in-reply-to:references:date :message-id:mime-version; bh=NU17Yq/AK4USZPcdc43DTuLWNe9T5lZq4o05Tuv7xGk=; b=KayuKQEob2N9twEwsuwf1MzJDDba8/goX/X9p1uq1WxcatX7wT3OYHwe33W2Ceu5eB 4djul0Z/+yhI7ENT1I6TJtnCypGU0oXa0oUfLRVtXS5mQ+iac+UaUHWeI817IdwuwhLC +7wTfvCQu4E83zNobSLA4wIYUA0sA1jrT1VWrFjLZ7mVdwe96pl9pQ4ZGrculLB0Ep7k c2krrMb3seizriPc+MwIDG2EnOxPqQS8/czwuV8uF6fRb8a3cr/PZYwdVqoRO7m9gGkG zPnfeYSrBUD2QAV1d+PFApWBwoF/xoKFlcXYfeu1xZFVl9AQJYwpCDVg856oeCGcrX0x OBFg== X-Gm-Message-State: APjAAAW1YIHxd4z56q2grsrenNWRWfPYLUxfgIHLILBv9mawdxeQf5Dw aKT3KvAHBcyn46DfOacSakcgI48T5JI1rp8w7oV/SCWzoguDCYY07s6Ac2yqPjrwR7ugAI7OFUf Ta8m+WkMgf0v/ X-Received: by 2002:a05:6000:d:: with SMTP id h13mr2901724wrx.346.1570624460998; Wed, 09 Oct 2019 05:34:20 -0700 (PDT) X-Google-Smtp-Source: APXvYqz4krLMd42RXMqGzfozS0sdlYRgeYvbnnDan0LJVeGhK6peLuktJv7VzxKNfuT+j3QL6TMzEA== X-Received: by 2002:a05:6000:d:: with SMTP id h13mr2901711wrx.346.1570624460804; Wed, 09 Oct 2019 05:34:20 -0700 (PDT) Received: from vitty.brq.redhat.com (nat-pool-brq-t.redhat.com. [213.175.37.10]) by smtp.gmail.com with ESMTPSA id u7sm3181752wrp.19.2019.10.09.05.34.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 09 Oct 2019 05:34:20 -0700 (PDT) From: Vitaly Kuznetsov To: Paolo Bonzini Cc: Jim Mattson , Aaron Lewis , Babu Moger , Yang Weijiang , Sebastian Andrzej Siewior , kvm@vger.kernel.org Subject: Re: [Patch 2/6] KVM: VMX: Use wrmsr for switching between guest and host IA32_XSS In-Reply-To: References: <20191009004142.225377-1-aaronlewis@google.com> <20191009004142.225377-2-aaronlewis@google.com> Date: Wed, 09 Oct 2019 14:34:19 +0200 Message-ID: <871rvmyu5w.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Paolo Bonzini writes: > On 09/10/19 02:41, Aaron Lewis wrote: >> Set IA32_XSS for the guest and host during VM Enter and VM Exit >> transitions rather than by using the MSR-load areas. >> >> Reviewed-by: Jim Mattson >> Signed-off-by: Aaron Lewis > > This commit message is missing an explanation of why this is a good thing. > > Also, the series is missing a cover letter that explains a bit more of > the overall picture. I have no problem with no cover letter for > two-patch series, but at six it is definitely a requirement. > > So I'm replying to this patch as a proxy for the whole series, and > asking: why is it useful to enable XSAVES (on AMD or anywhere) if anyway > IA32_XSS is limited to zero? I know at least one good reason to do so: Hyper-V 2016 Gen1 (but not Gen2!) doesn't seem to be able to boot without XSAVES (don't ask me why). I'm not particularly sure if Aaron is aiming at fixing this one though. -- Vitaly