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[209.132.180.67]) by mx.google.com with ESMTP id b17si8505784pgu.407.2018.03.05.08.49.20; Mon, 05 Mar 2018 08:49:34 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; dkim=pass header.i=@linaro.org header.s=google header.b=IqtlD7Yt; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=linaro.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752460AbeCEQsR (ORCPT + 99 others); Mon, 5 Mar 2018 11:48:17 -0500 Received: from mail-ot0-f181.google.com ([74.125.82.181]:46639 "EHLO mail-ot0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751311AbeCEQsQ (ORCPT ); Mon, 5 Mar 2018 11:48:16 -0500 Received: by mail-ot0-f181.google.com with SMTP id g97so15502782otg.13 for ; Mon, 05 Mar 2018 08:48:15 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc; bh=Teo4weLKhqRLnN7/Y6+HUN2rV9HXEs+DE9qu7zdpQAc=; b=IqtlD7YtipQi8MUOnPx7Ucjfsvr4aZZ/V5YmH1tY/hE0o6xBNlzbBgqzIY0QJ4/Isl f956KN4LsvYleJtcTLKVwEAfM3I779PvbsWKIcpNaczuROtd2Urvb/6+6uFjs6uwIgBZ x0HjrHkUlo0LVDAXk5/WIB/7ccAIIiaowQLWg= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc; bh=Teo4weLKhqRLnN7/Y6+HUN2rV9HXEs+DE9qu7zdpQAc=; b=fGBKoXbBzgSzppysKMIekGd26OXQhQnx2H1c/UQP/5QyHTBVGJeqp5J9tQ9ITr8wgJ mqeFN08nKDib8Cnnsqqkgl1JK2G1R86uuTHCj91gHw2VBVbDY3FdVE3eZNQvFkv81E5q FKP8YogSF2lEPcGUphPhUNzCQpQqkDrZfscS748xt/0Uryu5rtxXwnkTUpMftyG7a6um 6vKSnTaq3FhkAPH9h6kGozKxpvBrB5MZr0oUbn2yn18bUiQuddctSYQkoMRh7iftVpN7 rRDax382Pq5T7IXaIYFReadBK8F6r3EZcuFahFYEDSC5PQgslmkLJo1+EtTq7prefy4E udxw== X-Gm-Message-State: APf1xPBsP3jk+UgyoGIjLILoLSzD/7KwkTt8mx6Dm+jIpqVaIKeVSiNi rHKzRVjtMcstlTEwtm29e/M0W95jvJ/P2Qgc97smHA== X-Received: by 10.157.72.231 with SMTP id a36mr11263438otj.308.1520268495478; Mon, 05 Mar 2018 08:48:15 -0800 (PST) MIME-Version: 1.0 Received: by 10.157.33.100 with HTTP; Mon, 5 Mar 2018 08:47:55 -0800 (PST) In-Reply-To: <86o9k63f7a.wl-marc.zyngier@arm.com> References: <20180215175803.6870-1-marc.zyngier@arm.com> <86o9k63f7a.wl-marc.zyngier@arm.com> From: Peter Maydell Date: Mon, 5 Mar 2018 16:47:55 +0000 Message-ID: Subject: Re: [REPOST PATCH] arm/arm64: KVM: Add PSCI version selection API To: Marc Zyngier Cc: Auger Eric , lkml - Kernel Mailing List , arm-mail-list , kvmarm@lists.cs.columbia.edu Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2 March 2018 at 11:11, Marc Zyngier wrote: > On Fri, 02 Mar 2018 10:44:48 +0000, > Auger Eric wrote: >> I understand the get/set is called as part of the migration process. >> So my understanding is the benefit of this series is migration fails in >> those cases: >> >> >=0.2 source -> 0.1 destination >> 0.1 source -> >=0.2 destination > > It also fails in the case where you migrate a 1.0 guest to something > that cannot support it. I think it would be useful if we could write out the various combinations of source, destination and what we expect/want to have happen. My gut feeling here is that we're sacrificing exact migration compatibility in favour of having the guest automatically get the variant-2 mitigations, but it's not clear to me exactly which migration combinations that's intended to happen for. Marc? If this wasn't a mitigation issue the desired behaviour would be straightforward: * kernel should default to 0.2 on the basis that that's what it did before * new QEMU version should enable 1.0 by default for virt-2.12 and 0.2 for virt-2.11 and earlier * PSCI version info shouldn't appear in migration stream unless it's something other than 0.2 But that would leave some setups (which?) unnecessarily without the mitigation, so we're not doing that. The question is, exactly what *are* we aiming for? thanks -- PMM