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,URIBL_BLOCKED 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 ED834C433E3 for ; Tue, 21 Jul 2020 05:41:20 +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 2BA4720792 for ; Tue, 21 Jul 2020 05:41:20 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=gibson.dropbear.id.au header.i=@gibson.dropbear.id.au header.b="ew0jBvgE" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2BA4720792 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=gibson.dropbear.id.au 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 4B9nWx1bQ5zDqTn for ; Tue, 21 Jul 2020 15:41:17 +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 4B9nTs6D7NzDqTn for ; Tue, 21 Jul 2020 15:39:29 +1000 (AEST) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=gibson.dropbear.id.au Authentication-Results: lists.ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=gibson.dropbear.id.au header.i=@gibson.dropbear.id.au header.a=rsa-sha256 header.s=201602 header.b=ew0jBvgE; dkim-atps=neutral Received: by ozlabs.org (Postfix, from userid 1007) id 4B9nTs3QKjz9sRk; Tue, 21 Jul 2020 15:39:29 +1000 (AEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gibson.dropbear.id.au; s=201602; t=1595309969; bh=J4UScPRMK9eRPaOWcVp7O8JSp1ZFqU5+OaPm5aZhMDM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=ew0jBvgEc77aF6Dzo8vZ0zTFSU7A/eVeUpwxMb7sc8LXPLmeZarmkdt6KXV+Ka23T gQ222dPYsavkOxvXGANiKRYnTqwypD2JaPcw1sT8K8dTEvdE8GrJ1dMr0WCP6p1Xw+ RlZYTPrTuLm8dypOfPqV1qAwOf0AOOv5JTlQdjto= Date: Tue, 21 Jul 2020 15:39:25 +1000 From: David Gibson To: Paul Mackerras Subject: Re: [PATCH] KVM: PPC: Book3S HV: Use feature flag CPU_FTR_P9_TIDR when accessing TIDR Message-ID: <20200721053925.GG215446@umbus.fritz.box> References: <20200623165027.271215-1-clg@kaod.org> <20200721050445.GA3878639@thinks.paulus.ozlabs.org> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="VSVNCtZB1QZ8vhj+" Content-Disposition: inline In-Reply-To: <20200721050445.GA3878639@thinks.paulus.ozlabs.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: kvm-ppc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, =?iso-8859-1?Q?C=E9dric?= Le Goater , kvm@vger.kernel.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" --VSVNCtZB1QZ8vhj+ Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Jul 21, 2020 at 03:04:45PM +1000, Paul Mackerras wrote: > On Tue, Jun 23, 2020 at 06:50:27PM +0200, C=E9dric 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. >=20 > 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. Having thought about this a bit more, I don't think it matters. We're going to have to update qemu to handle POWER10 anyway. If this causes a problem, this would just add one small thing to whatever we need to fix there. > 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. --=20 David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. 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