From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-180.mta0.migadu.com (out-180.mta0.migadu.com [91.218.175.180]) (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 87DBB286A8 for ; Wed, 12 Jun 2024 05:31:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.180 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1718170263; cv=none; b=mAcwXeNLVJuNHq4T9sMzgU7EIgw3KQcqtuhw3RNOM/BkrBDQGMtWNmEPrDOR9a52HZfMihhfv0kAAd+lg7yjB+M+zi1niEB/GOKueLTSf5HkbDlDP85LNLcAHA2NY8bk+H9k6gIIMAX7ciL+NLa3iLGb/lDbMIlnsdeF6vSjeTo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1718170263; c=relaxed/simple; bh=M79FP9xawocEU+lriIXIatL6EDmqJHLQLEu2xZP59cE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=T/CZv8Zt1IajFVrLAuswSELjIytPtSHoHrzwMXUQjs8XfIX2X3an9yq1d8f/H8ZU+OcugLz4Ed63i5jQ7rcFV6CaTBNHkebHkM3bQevenncggec6nxGv643HfgXXyCBZcvMhdyBBxKGVNIbvJllDqrOF0J98riKTHUTB8mq9prE= 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=qXr+DAg8; arc=none smtp.client-ip=91.218.175.180 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="qXr+DAg8" X-Envelope-To: shahuang@redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1718170259; 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=/UiRVtVLigMQeE81g8Kpmn0pUJ/eW6cDDy3LoMW/VXc=; b=qXr+DAg8cKacFvDiSUke0+CGHdsYkHAmAXVnXnPbCZTIdT4ICUniQacRM8YvMnGHJsOFdY diLKnRd3TYks2/vlYheRAZEPOKxV2nCgdMwl21BghyUTzHBFWCzo/zfvIUM+oA0YvNQGpT ysoU3sMV2TcI+Fq3yT58ywcIQaau6e8= X-Envelope-To: maz@kernel.org X-Envelope-To: kvmarm@lists.linux.dev X-Envelope-To: eauger@redhat.com X-Envelope-To: sebott@redhat.com X-Envelope-To: cohuck@redhat.com X-Envelope-To: catalin.marinas@arm.com X-Envelope-To: james.morse@arm.com X-Envelope-To: kvm@vger.kernel.org X-Envelope-To: linux-arm-kernel@lists.infradead.org X-Envelope-To: linux-kernel@vger.kernel.org X-Envelope-To: linux-kselftest@vger.kernel.org X-Envelope-To: pbonzini@redhat.com X-Envelope-To: shuah@kernel.org X-Envelope-To: suzuki.poulose@arm.com X-Envelope-To: will@kernel.org X-Envelope-To: yuzenghui@huawei.com Date: Tue, 11 Jun 2024 22:30:51 -0700 X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Oliver Upton To: Shaoqin Huang Cc: Marc Zyngier , kvmarm@lists.linux.dev, Eric Auger , Sebastian Ott , Cornelia Huck , Catalin Marinas , James Morse , kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Paolo Bonzini , Shuah Khan , Suzuki K Poulose , Will Deacon , Zenghui Yu Subject: Re: [RFC PATCH v1 0/2] KVM: arm64: Making BT Field in ID_AA64PFR1_EL1 writable Message-ID: References: <20240612023553.127813-1-shahuang@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: <20240612023553.127813-1-shahuang@redhat.com> X-Migadu-Flow: FLOW_OUT Hi Shaoqin, On Tue, Jun 11, 2024 at 10:35:50PM -0400, Shaoqin Huang wrote: > Hi guys, > > I'm trying to enable migration from MtCollins(Ampere Altra, ARMv8.2+) to > AmpereOne(AmpereOne, ARMv8.6+), the migration always fails when migration from > MtCollins to AmpereOne due to some register fields differing between the > two machines. > > In this patch series, we try to make more register fields writable like > ID_AA64PFR1_EL1.BT. This is first step towards making the migration possible. > Some other hurdles need to be overcome. This is not sufficient to make the > migration successful from MtCollins to AmpereOne. It isn't possible to transparently migrate between these systems. The former has a cntfrq of 25MHz, and the latter has a cntfrq of 1GHz. There isn't a mechanism for scaling the counter frequency, and I have zero appetite for a paravirt interface. On top of that, erratum AC03_CPU_38 seems to make a migration from Neoverse-N1 to AmpereOne quite perilous, unless you hide FEAT_HAFDBS on the source. These issues are separate, though, from any possible changes to the writability of ID_AA64PFR1_EL1, which still may be useful to userspace. -- Thanks, Oliver