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_INVALID, DKIM_SIGNED,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 E404FC433DF for ; Tue, 21 Jul 2020 05:06:34 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (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 8FF77206E9 for ; Tue, 21 Jul 2020 05:06:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=ozlabs.org header.i=@ozlabs.org header.b="DivInJNu" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8FF77206E9 Authentication-Results: mail.kernel.org; dmarc=pass (p=none dis=none) header.from=ozlabs.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 4B9mlr3jcBzDqgV for ; Tue, 21 Jul 2020 15:06:32 +1000 (AEST) Received: from ozlabs.org (bilbo.ozlabs.org [IPv6:2401:3900:2:1::2]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4B9mjt4SsdzDqVB for ; Tue, 21 Jul 2020 15:04:50 +1000 (AEST) Authentication-Results: lists.ozlabs.org; dmarc=pass (p=none dis=none) header.from=ozlabs.org Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; secure) header.d=ozlabs.org header.i=@ozlabs.org header.a=rsa-sha256 header.s=201707 header.b=DivInJNu; dkim-atps=neutral Received: by ozlabs.org (Postfix, from userid 1003) id 4B9mjt342fz9sSJ; Tue, 21 Jul 2020 15:04:50 +1000 (AEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ozlabs.org; s=201707; t=1595307890; bh=F77WFg+4dndurqYjYW+EYiJiX3wkHQ0Go7Hn9Xv1mhY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=DivInJNueA+UccbiuANm5nHiHdMSq1dBegGb0Qi7XOrxUwx8qMXEe14MxEW4C9bWJ VfjM0sYFtB5ndIRadWr57LjUNrnzvoP4GSzN8twwv3qGFtm4xc3H1dXY+d2O3Pd5ib e6JM0ZVmoD8b35ixh03vQ2VUiy48z8q+pQ4dQ7Quli0av6un79xsnGfEbv9x/F3iRk LGodlffg7TZG5Y7OYCxIFbj+3LoFJV2uwMLVjarNIeFlJE0IVtGJXgjzuCimK0ZNmG 83dgoFx2Nl7AC4/xqPw9lJ0QVe1LqhhkxIRSLWN2yRs+MR7jtNkhG56D3tXpKyLKT9 r1oATtEG7PkpQ== Date: Tue, 21 Jul 2020 15:04:45 +1000 From: Paul Mackerras To: =?iso-8859-1?Q?C=E9dric?= Le Goater Subject: Re: [PATCH] KVM: PPC: Book3S HV: Use feature flag CPU_FTR_P9_TIDR when accessing TIDR Message-ID: <20200721050445.GA3878639@thinks.paulus.ozlabs.org> References: <20200623165027.271215-1-clg@kaod.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20200623165027.271215-1-clg@kaod.org> X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linuxppc-dev@lists.ozlabs.org, kvm-ppc@vger.kernel.org, kvm@vger.kernel.org, David Gibson Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Tue, Jun 23, 2020 at 06:50:27PM +0200, Cédric Le Goater wrote: > The TIDR register is only available on POWER9 systems and code > accessing this register is not always protected by the CPU_FTR_P9_TIDR > flag. Fix that to make sure POWER10 systems won't use it as TIDR has > been removed. I'm concerned about what this patch would do if we are trying to migrate from a P9 guest to a guest on P10 in P9-compat mode, in that the destination QEMU would get an error on doing the SET_ONE_REG for the TIDR. I don't think the lack of TIDR is worth failing the migration for given that TIDR only actually does anything if you are using an accelerator, and KVM has never supported use of accelerators in guests. I'm cc'ing David Gibson for his comments on the compatibility and migration issues. In any case, given that both move to and move from TIDR will be no-ops on P10 (for privileged code), I don't think there is a great urgency for this patch. Paul.