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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 518AEC77B7F for ; Tue, 16 May 2023 13:12:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Subject:Cc:To:From:Message-ID:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=zlP3l+/LAE12EZ81XkoJHomuz6zuVdsrAFL9JaBcoDk=; b=k+z46RXSrMudDJ ozFDM1xbgalHP5DXoE7TesSC9llNCfj/37ngp7s7lPCmMprD8+zY3oQNZGIi8J7tIzk60H6tTNEdc 1Dy1C7oimPVigKV9GhPtZuN7wgCYjvxEydvCYNAghg193IKSjQRM2vEZyYjRS2SG/6WGfsBEW3uHD IV0Y8XnT5vDsI3SbU14fuFr+EcqBuyclKMmenH0vKQBoAjgJbaFdNasIcDbLcMAkMrm8e74hLZFUr 63qFFF9wT165cR6M0g5fa9G4ZEEXm5uEA3aJwlxQLC3IfiGAjn39Ek0uwbehlI7lduJNHTDpeWQ+n oYlEnZtxMAcQAb/F8Hug==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1pyuSm-005rOc-1H; Tue, 16 May 2023 13:11:36 +0000 Received: from dfw.source.kernel.org ([2604:1380:4641:c500::1]) by bombadil.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1pyuSj-005rO5-2O for linux-arm-kernel@lists.infradead.org; Tue, 16 May 2023 13:11:35 +0000 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 1AD5362DB7; Tue, 16 May 2023 13:11:33 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 724E7C433D2; Tue, 16 May 2023 13:11:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1684242692; bh=IJsMGoud7bTgHYYbedTM5y6Eb34rX7hOhJN1b6kykfU=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=LK+bVF/5Z1JNGB1HcqBAUvUoSTK/dIyhQXtKGtZhCFdOX838n5Vl9DZh3P6AJKmy8 +plzXsfqoH3aebWLp+5lPHyspxKEhq1yyZHqHw9QeQZjV5TtxrMX52natFO8Db7X9O F+KBLC28gB23BIIkGE1Bc/QDE0AyxZ3CLsq/WBxt2O5B2tz0zij4smpzubvIW4ZTS2 gevS1MTf6nMPIpQ/Aon/6VdfjDetb4QMI2SN9ZRCG3I5ALMqX24WrKEdOjHwD+Dn8X n9PQrqMuhMubEn1NZCWiHZ6HPT/w9T5DNAhpEA4LxGZcYw5ryLztvDbnuJ+bes3S2j 4x10l8TMnahQw== Received: from sofa.misterjones.org ([185.219.108.64] helo=goblin-girl.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.95) (envelope-from ) id 1pyuSg-00FXpL-Dd; Tue, 16 May 2023 14:11:30 +0100 Date: Tue, 16 May 2023 14:11:30 +0100 Message-ID: <867ct8mnel.wl-maz@kernel.org> From: Marc Zyngier To: Cornelia Huck Cc: Shameerali Kolothum Thodi , Jing Zhang , KVM , KVMARM , ARMLinux , Oliver Upton , Will Deacon , Paolo Bonzini , James Morse , Alexandru Elisei , Suzuki K Poulose , Fuad Tabba , Reiji Watanabe , Raghavendra Rao Ananta Subject: Re: [PATCH v8 0/6] Support writable CPU ID registers from userspace In-Reply-To: <87cz30h4nx.fsf@redhat.com> References: <20230503171618.2020461-1-jingzhangos@google.com> <2ef9208dabe44f5db445a1061a0d5918@huawei.com> <868rdomtfo.wl-maz@kernel.org> <1a96a72e87684e2fb3f8c77e32516d04@huawei.com> <87cz30h4nx.fsf@redhat.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/28.2 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: cohuck@redhat.com, shameerali.kolothum.thodi@huawei.com, jingzhangos@google.com, kvm@vger.kernel.org, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, oupton@google.com, will@kernel.org, pbonzini@redhat.com, james.morse@arm.com, alexandru.elisei@arm.com, suzuki.poulose@arm.com, tabba@google.com, reijiw@google.com, rananta@google.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230516_061133_869359_3D1CCB1B X-CRM114-Status: GOOD ( 19.12 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, 16 May 2023 12:55:14 +0100, Cornelia Huck wrote: > > Do you have more concrete ideas for QEMU CPU models already? Asking > because I wanted to talk about this at KVM Forum, so collecting what > others would like to do seems like a good idea :) I'm not being asked, but I'll share my thoughts anyway! ;-) I don't think CPU models are necessarily the most important thing. Specially when you look at the diversity of the ecosystem (and even the same CPU can be configured in different ways at integration time). Case in point, Neoverse N1 which can have its I/D caches made coherent or not. And the guest really wants to know which one it is (you can only lie in one direction). But being able to control the feature set exposed to the guest from userspace is a huge benefit in terms of migration. Now, this is only half of the problem (and we're back to the CPU model): most of these CPUs have various degrees of brokenness. Most of the workarounds have to be implemented by the guest, and are keyed on the MIDR values. So somehow, you need to be able to expose *all* the possible MIDR values that a guest can observe in its lifetime. I have a vague prototype for that that I'd need to dust off and finish, because that's also needed for this very silly construct called big-little... Thanks, M. -- Without deviation from the norm, progress is not possible. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel