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=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,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 1568EC433C1 for ; Mon, 29 Mar 2021 17:44:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B63626024A for ; Mon, 29 Mar 2021 17:44:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230385AbhC2Rne (ORCPT ); Mon, 29 Mar 2021 13:43:34 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59226 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230437AbhC2RnK (ORCPT ); Mon, 29 Mar 2021 13:43:10 -0400 Received: from mail-pj1-x102a.google.com (mail-pj1-x102a.google.com [IPv6:2607:f8b0:4864:20::102a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 89B61C061574 for ; Mon, 29 Mar 2021 10:43:10 -0700 (PDT) Received: by mail-pj1-x102a.google.com with SMTP id x21-20020a17090a5315b029012c4a622e4aso5537650pjh.2 for ; Mon, 29 Mar 2021 10:43:10 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amacapital-net.20150623.gappssmtp.com; s=20150623; h=content-transfer-encoding:from:mime-version:subject:date:message-id :references:cc:in-reply-to:to; bh=Z6t4O1RYVUyxfnLHWVRPLJFIbpkzHLyD7hxqplzKA4M=; b=gLMohOAGYhCGb6LRh6BSEina138WNXhAys9t8Oc4R2GhmbTB3EeFsp16Pg6YbniYGN MqlJ2WdU6OvpeHEPizCrcgHdMt2yWp4CrQbBTkp0tDcY6hadne66FYLx3LvmMnxGK7CT 2LpYVqJjkntMOJF9DiTyjvs48CW2EklqivnXyo8fOG21UBK3rh3ETCudY73pJ39vGPU1 OMXnjAUrD9Qef55KxyPlafcV6cf+NPpb6ueeXR2UOFgRY24NIgVhTVOH8EV6Ip3nPt4v EbiL2IhyW/NbFTIBwxVGDIp81LebVBrxJ/v534CpmXKPvrzmZv8UBkIGOLbWKd0a4hJk NgXw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:content-transfer-encoding:from:mime-version :subject:date:message-id:references:cc:in-reply-to:to; bh=Z6t4O1RYVUyxfnLHWVRPLJFIbpkzHLyD7hxqplzKA4M=; b=HYFhzXSQp52hXM5ctIuZeAGTv8Rk9JvkOa/TeQp0NekfT0JGeOVrEGx6YZj8fFIjom +Eg/L0tue9IaTt1g4PepKR+Dcf66aX/ENLq4hOZRBs0xu/svuGvJW0VVpny5yQx50Nq8 Nyl5d7JzCwvs7pa+mu4YTlaeEIZAyogZNGStF5963/+hv+4jxIWjg6hH/sSc3m9l21vj r7/K64lCNV+vMIDr37aijODV2gvGRvn81Kc1sVXMGN637jKagtvZOhfdEckXJA5wwfqJ WzOsCVhCFK3dckapZ9n/AbF50ThG+noY2YFsN54FUJTloHyuB0L3QFOGmnlznt70wh5O aUPg== X-Gm-Message-State: AOAM531Ll7mS+iAjRLnrUTCFGRI1fL4O67XnKFPC5CeW0C/SSTIjlq/r EkeRx73UNRtnu4ApFWOaUcAT8g== X-Google-Smtp-Source: ABdhPJyhxU9RzMMXlogKIDMvRFNS8XrXutmNrsOIY/4iBlP04fOsR7l8yS6aHgFEHYEgZ6nI3qwHNA== X-Received: by 2002:a17:90b:ecd:: with SMTP id gz13mr218628pjb.219.1617039790046; Mon, 29 Mar 2021 10:43:10 -0700 (PDT) Received: from ?IPv6:2600:1010:b06a:1311:e806:6d31:5a5:2c5c? ([2600:1010:b06a:1311:e806:6d31:5a5:2c5c]) by smtp.gmail.com with ESMTPSA id g10sm16590978pgh.36.2021.03.29.10.43.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 29 Mar 2021 10:43:09 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable From: Andy Lutomirski Mime-Version: 1.0 (1.0) Subject: Re: [PATCH v4 14/22] x86/fpu/xstate: Expand the xstate buffer on the first use of dynamic user state Date: Mon, 29 Mar 2021 10:43:05 -0700 Message-Id: <09AB34BD-7DB8-4DBD-A538-F3AE642F8C8A@amacapital.net> References: Cc: Thomas Gleixner , "Chang S. Bae" , Borislav Petkov , Andy Lutomirski , Ingo Molnar , X86 ML , "Brown, Len" , Dave Hansen , "Liu, Jing2" , "Ravi V. Shankar" , Linux Kernel Mailing List In-Reply-To: To: Len Brown X-Mailer: iPhone Mail (18D61) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Mar 29, 2021, at 9:06 AM, Len Brown wrote: >=20 > =EF=BB=BFOn Mon, Mar 29, 2021 at 11:43 AM Len Brown wrot= e: >>=20 >> On Mon, Mar 29, 2021 at 9:33 AM Thomas Gleixner wrot= e: >>=20 >>>> I found the author of this passage, and he agreed to revise it to say t= his >>>> was targeted primarily at VMMs. >>>=20 >>> Why would this only a problem for VMMs? >>=20 >> VMMs may have to emulate different hardware for different guest OS's, >> and they would likely "context switch" XCR0 to achieve that. >>=20 >> As switching XCR0 at run-time would confuse the heck out of user-space, >> it was not imagined that a bare-metal OS would do that. >=20 > to clarify... > *switching* XCR0 on context switch is slow, but perfectly legal. How slow is it? And how slow is switching XFD? XFD is definitely serializi= ng?