From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-171.mta1.migadu.com (out-171.mta1.migadu.com [95.215.58.171]) (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 954F22571D0 for ; Mon, 24 Feb 2025 22:23:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.171 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740435808; cv=none; b=b7am/Ei0ikC2b5M7t/gWHle+jZrSX8RdRhUS9EdbQIblF2BO8mRdlsITYt1kMfChbVtcN8/tBzpkAeJlcF3bL0frx6T2IPwVbQkauGvUF+7ns2ocUoPqRH6jHwnFR/bwxNdkwKvKxMzh1jF3EFECuJke1vKghwi5KLQc+nuC850= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740435808; c=relaxed/simple; bh=qmooO3AxZOs0ohQpJ4yo5y4Yi0jidhmcv0CFom4ARm0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=CpRtqy3O8V0ztxmAqZ6gG8yKFsMRtUcpamWWdvRzypYh2sIPg/nzED7NILNzaOVpm0uedUFr/Y4pe+TDQo925Go5klpRXDpHjpNPALCCTWYQJKmNpPwtGenDKHk+b7Fuvf4+Qc6lqNKJHR+W7OZKxv2Xzj57PEy4jMTb8ho1q7s= 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=maOIQzSv; arc=none smtp.client-ip=95.215.58.171 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="maOIQzSv" 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> 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: <20250218163443.32836-1-sebott@redhat.com> X-Migadu-Flow: FLOW_OUT 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