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 9A8E1C021A4 for ; Mon, 24 Feb 2025 22:24:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=MytlJ2KGkzQ+RhdKVpvDJ1qR08yPF+KOv8QGFyqerQs=; b=w8qvxHvJEfu+mQ92s+KemNYrtf Ww5k6gz2b4sBi/KNUpzhDwWAI5yBCZk679uROITJ5uL/61ypq8s3qQh+yt7WjtT9Avg1AqUdbLENs jQ3PN7yTt80BkozrFVbNyANtPcnqS0IkYHCVXYrV5TYTYsCCb4WI/IdaY8Eqk4h7aXSVj9ba0GSIk lB7RlNrFP40SOnUe8v4hnzX4rpceULaRn0RlexkrRpsx4AVymrY7Tti9pLvRv7ujrPpmIFDXbkMX3 ysNrOG6Mzq7VrrDEiZqpClbTe8CnkHaOObsvST8VFnXlqSr0bnVGEyTuRADi5eX8QpW3WU/gzW9S2 g2DHQODA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tmgsb-0000000FMJe-1Hal; Mon, 24 Feb 2025 22:24:49 +0000 Received: from out-178.mta1.migadu.com ([2001:41d0:203:375::b2]) by bombadil.infradead.org with esmtps (Exim 4.98 #2 (Red Hat Linux)) id 1tmgr7-0000000FM2N-01yf for linux-arm-kernel@lists.infradead.org; Mon, 24 Feb 2025 22:23:18 +0000 Date: Mon, 24 Feb 2025 14:23:05 -0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1740435794; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=MytlJ2KGkzQ+RhdKVpvDJ1qR08yPF+KOv8QGFyqerQs=; b=maOIQzSvuUUmYk2SXkgSfup4ufEe8vHbBJ1FJO81wU3bAJfRUFrahN1yRRh9znIPT/o5TV WoB9p4K7A8zLUuGiNJ6GriZ8DtNyq3pPrqY+zl2aOneRbzq2EQxRQ9awhbiIE8t+IhjSRU HIruwKqVpJtTTT00ZjwDqRmDWWixvoY= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Oliver Upton To: Sebastian Ott Cc: Marc Zyngier , Joey Gouly , Suzuki K Poulose , Zenghui Yu , Catalin Marinas , Will Deacon , Shameer Kolothum , Cornelia Huck , Eric Auger , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 0/4] KVM: arm64: writable MIDR/REVIDR Message-ID: References: <20250218163443.32836-1-sebott@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250218163443.32836-1-sebott@redhat.com> X-Migadu-Flow: FLOW_OUT X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250224_142317_188274_92F4B223 X-CRM114-Status: GOOD ( 11.95 ) 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: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Sebastian, On Tue, Feb 18, 2025 at 05:34:39PM +0100, Sebastian Ott wrote: > Based on prior discussion [1] this series allows VMMs to change > MIDR/REVIDR to enable migration between machines that differ in > these registers. Since these are used for errata handling the > errata management series [2] is a prerequisite for this one. > > changes for V3: > * handle VPIDR_EL2 as part of vcpu ctxt - thanks Oliver! Thanks for respinning. While your changes are looking good, as I got ready to apply this series I wound up peeling the onion a bit further and have a few more concerns: - Current KVM allows guests to read SMIDR_EL1 despite the fact that we do not support SME (this is part of TID1 traps) - The "invariant" values that KVM presents to userspace originate from the boot CPU, not the CPU that resets the ID registers for a VM - A VMM that wants to present big-little can do so on current KVM by affining vCPUs, but cannot with this series All of this is to say, I think your series is going to collide with the pre-existing pile of crap we have. I'm going to pick up these changes and rework them so we can send a fix for #1 to stable trees and (hopefully) avoid breaking the old "invariant" behavior. I'll post what I have as soon as I test it, hopefully we can get this shaped up for 6.15. Thanks, Oliver