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 1C040C4332F for ; Wed, 23 Nov 2022 18:18:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239644AbiKWSSI (ORCPT ); Wed, 23 Nov 2022 13:18:08 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43782 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239582AbiKWSRt (ORCPT ); Wed, 23 Nov 2022 13:17:49 -0500 Received: from mail-pj1-x1030.google.com (mail-pj1-x1030.google.com [IPv6:2607:f8b0:4864:20::1030]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7CDF810FC7 for ; Wed, 23 Nov 2022 10:16:26 -0800 (PST) Received: by mail-pj1-x1030.google.com with SMTP id a1-20020a17090abe0100b00218a7df7789so2822806pjs.5 for ; Wed, 23 Nov 2022 10:16:26 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:from:date:from:to :cc:subject:date:message-id:reply-to; bh=tPtG6fZZhKtGLftjAJCGFWjxf1W8gNx6BzHO8wa+RDY=; b=n+sWxH04gAVH9IaWSdVXB27EzzqDQRv8kExFSiEKcT/FrhFpF50phN8ImDhmJjB4Uv kLVYklIplhJ3RCJF7H8no9ZuJVCwTld3OhYEX4hs0wfgSNV/MP4XRBJ+9PhSC4R/6qZW PFSNjcyPB37Ptq4ag1XKo7AGQfOtow9z//E56zdRBaXkhnCag1TONnxCPjoXwW2l6SPv uf55CgnmFO2WsWyC7X4DUjUIZ3duz/52XwqlR1mINLUkK08KOjUZf3ruyQIZOWHPG+Qs cx2jA/vp+oFdP8dzoQdaa1GoTM+IIkTy85vbEFTYIvqBa928XvNCwe1zZzTGvY16kHmb 0WpA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:from:date :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=tPtG6fZZhKtGLftjAJCGFWjxf1W8gNx6BzHO8wa+RDY=; b=u68kinL3IpDeleEnKnW7ml2CJxG7/0VzcLjMn7DmzzonC5/6y5jez1mbrYFKePo0XM U0AhZKRr5R0ezUwtZ6qp0/6ovMlzf8ksCop8XLFOrYrE06VLhlNLtRqY2vu7RETdvX8I 5/Is76Llqch4EN66VRgqttzCr80f1NF/wM/bxh0ST7nSyUm5+VQOVzTDdUOWPm6Q4GbN xzFDCe8nFxZ8vNgGuF+/7G9JcCm+3E0coNWWJHR+vjZrYODVEMZNNd7dtwcPWi3tqsdN ZTu30kIU87apdvHEOV7FoYeCu7T05KM/3N/PFc1J/It7NMClFBITmJrZYMRUnQ6pLpPP +WiA== X-Gm-Message-State: ANoB5pltfA1mFdb8h/0/0F2euab0lEMeq5LIoISeHkFL3Ml3cpGmpjEG 33LDxxycKTBriZiKsl2WBuUqww+oZdo1VQ== X-Google-Smtp-Source: AA0mqf6Jkkz3t5x4GuMqI9rJ34J/1T1JWKCv1jVDMNDLXHs8MC687fBC20R4tLNWisJ8eXlpfFFfJA== X-Received: by 2002:a17:90a:cb11:b0:218:d772:ec60 with SMTP id z17-20020a17090acb1100b00218d772ec60mr6982300pjt.143.1669227385878; Wed, 23 Nov 2022 10:16:25 -0800 (PST) Received: from google.com (7.104.168.34.bc.googleusercontent.com. [34.168.104.7]) by smtp.gmail.com with ESMTPSA id p10-20020a170902780a00b0017ec1b1bf9fsm8845536pll.217.2022.11.23.10.16.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 23 Nov 2022 10:16:25 -0800 (PST) Date: Wed, 23 Nov 2022 18:16:21 +0000 From: Sean Christopherson To: David Woodhouse Cc: Paolo Bonzini , kvm@vger.kernel.org, mhal@rbox.co Subject: Re: [PATCH 2/4] KVM: x86/xen: Compatibility fixes for shared runstate area Message-ID: References: <20221119094659.11868-1-dwmw2@infradead.org> <20221119094659.11868-2-dwmw2@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Wed, Nov 23, 2022, David Woodhouse wrote: > On Wed, 2022-11-23 at 17:17 +0000, Sean Christopherson wrote: > And with or without that cache, we can *still* end up doing a partial > update if the page goes away. The byte with the XEN_RUNSTATE_UPDATE bit > might still be accessible, but bets are off about what state the rest > of the structure is in — and those runtimes are supposed to add up, or > the guest is going to get unhappy. Ugh. What a terrible ABI. > I'm actually OK with locking two GPCs. It wasn't my first choice, but > it's reasonable enough IMO given that none of the alternatives jump out > as being particularly attractive either. I detest the two GPCs, but since KVM apparently needs to provide "all or nothing" updates, I don't see a better option.