From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-175.mta0.migadu.com (out-175.mta0.migadu.com [91.218.175.175]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7759F236449 for ; Wed, 26 Feb 2025 18:56:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.175 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740596190; cv=none; b=savRafudg7nwdW7BZ+z4xX0VXCEKGbia5kT57HyPG0cdT4OeaAI8dLPyUU8rDIdMEEFUxSWZz2atk57Jp+7BJDYRH62haS74yjPVdD8LAx5VJVHYEhb+DT7YaX0drB1vE3OFaA3otP1cOiAtLSckBxY9ZPEkl6OhB1n1+f5GzMo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740596190; c=relaxed/simple; bh=EUlIfdeF1pzupry08mNxqfWtBGYYyvkzaYg8I7GMfQg=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=uce8qilppa8rwugnZPDS/djzPhcQqX06sNDNpg29N8/MCIPfVJzZqICtoRWchbeeB9RFhJw0BdZUMYTinR98SBFcayeKarvxwx1U17QlrEcv2b1JLAWq6f+9Vp190PKAveHuBX/O4DkAwmsg2fhpdu1YzY93RE9te2dnh84fTxE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=DTrVl07I; arc=none smtp.client-ip=91.218.175.175 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="DTrVl07I" Date: Wed, 26 Feb 2025 10:56:21 -0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1740596186; 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=BSZAKZJBtmXPfCIzyN+pyGhW+GDpOa1dgPvIqwhe5V4=; b=DTrVl07ICp5qpVt9MAbJRYr2jB6odrQGw25//j+jiz92ZneaTgdDrKxpiezmpU/LqmQ43I JALYeNQ0rzYI+D5/Kg7jn9ve6YZsWTOq2pUMBN/fF/SjaKuW4hlJPRhK+IMYGRaD01KVOD /BMsU7qHDH6aVQa/frsYmyPqUVcg77s= 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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT On Wed, Feb 26, 2025 at 05:47:53PM +0100, Sebastian Ott wrote: > On Mon, 24 Feb 2025, Oliver Upton wrote: > > 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. > > Sry, for the additional work I've caused. I gave what you have in next a > spin and it looks good so far. > Thank you very much! Don't apologize -- it isn't your fault what we had already was a mess! :) Thanks for kicking the tires. Best, Oliver