From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793900871; b=UGbBS7JxRC7DCgXkJMgTttwydbKyUQaRl51U6ukZONbjz5EEsvZrly6xgMsNnv3HDPgP mIUOghzTGOJtCbFPZJMGnBkvlo0U/GC6IZdUUk8XUjZR9OANrpp0JbSrW7v7a6X0kHCKa hGRwqhVVpAeQPSqDP18DXJyMCZN1E29aFVEw+6N6gdVaZ9LlE9Bum5gSqQ6nfDEHvMVKO 1E/K/DRqxz169jAEz+RcclJpDe72JGVxzPVo2ERchRolbK2SyteLzTmfnH5JGb/aysoxd OKg9KsgIkM/6dizmXXeqQb0ijtSVACHxve1q6Oes1erZHamgCqTzLJ53YtITKs2CMrQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793900871; h=Received:DKIM-Signature:Date:From:To:Cc:Subject:Message-ID: References:MIME-Version:Content-Type:Content-Disposition:In-Reply-To; bh=yK5guq06GyB2POOrEH6V5+qRnqqw9aF5Y+PexajT4A4=; b=fHCiWbOc3g/6zTvlxfeWhpYDCe3Z6XPSeBopDSEdBQsn/qJ9oGgUbNkXt/1XwmXreRBV WJrJUZPKbEZV9nvTOHPvSjPT8Rlro1IkBhYLbaSMX3jzijF8JM/7uhl2KPmgYiQF2dxpl XQ/2sJRbX82v9ffDg8KeVRHtWa1kty33oQeOS510DUMFMTRw5C1VyxebuCpoLd6V33npc 6uyqhLqUScV5UdQK+8qidMppYoSYo9DmqPE5knQFnQYVbsfp+x6zAquhLzGufFhn7B8K6 PECmO/tbVtXT8Ltw5nSV04VlQ8/rUL9QRQ1+cGrmYGt0bQbL70TTrwnku0sz5Q1Gqqg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=UnPfYa3q; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 317F6606A328; Thu, 5 Nov 2026 17:47:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=UnPfYa3q Received: by smtp.kernel.org (Postfix) with ESMTPSA id 29EAC1F00919; Thu, 5 Nov 2026 17:47:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793900870; bh=yK5guq06GyB2POOrEH6V5+qRnqqw9aF5Y+PexajT4A4=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=UnPfYa3qDnqLQRHvVrNAuqpvDaJOJ6jHV4/9Jd5TTybeyTuR2OyeLNAuJTFs7rX74 WdurwevvTTlLMWrTN+MB/OG8bqZbWlno2jZcDxqc8v6r5x5eDVVKYWye0VDbOgCzS9 VnvjRlqdfPSOTPQNHP0WxkFApO6jZlD/ka496TCgdL52NPJAE573xfOxfF2qxK8fll wn5Amn07xx1cFgTDqBxL376qtOmGlb9aBEq70HVIbobk0ptY/VS7lM+xWSrrA/kw02 YgqNnPraKUOLNRVTyJzRdeSj+cwT1oRv9DlhuUkbMkiV4Gd9fZi3XeVp3Rn/Q9CKOl +siiQprvThIEA== Date: Thu, 5 Nov 2026 17:47:45 +0000 From: "Lorenzo Stoakes (ARM)" To: Alexandru Elisei Cc: maz@kernel.org, oupton@kernel.org, fuad.tabba@linux.dev, joey.gouly@arm.com, seiden@linux.ibm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, will@kernel.org, mark.rutland@arm.com, linux-perf-users@vger.kernel.org, catalin.marinas@arm.com, james.clark@linaro.org Subject: Re: [RFC PATCH v7 00/28] KVM: arm64: Add Statistical Profiling Extension (SPE) support Message-ID: References: <20260903160623.315525-1-alexandru.elisei@arm.com> X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260903160623.315525-1-alexandru.elisei@arm.com> Hi Alex, I've gone through all of the patches now, thank you for your patience with the review :) So there are various dependencies/architectural decisions that need to be made here to go from RFC -> non-RFC: 1. The 'Ignore MMU notifiers for guest_memfd-only memslots' patch [0] is a hard dependency for the series. I chased over there, hopefully we can get something landed there. 2. non-VHE, pKVM, NV disallowed for SPE - As I mentioned off-list, I spoke to Marc, and he confirmed that he's more than happy for these to be off the table for a v1. So I think you can drop the HACK: patches and just make these conditions of using SPE. 3. The entire VM needs to be pre-faulted, but who should do it? - I do think that relying on userland to do this is a little iffy. So I wonder whether it might be possible to, on SPE first run, prefault the ranges there, and make that a condition of using it? Relatedly, KVM could reject non-guest_memfd memslots for an SPE VM rather than trusting userspace there too. 4. Dirty page logging - patch 27/28 relies on series [1] being landed, which is also an RFC, and allows migration of SPE VMs. So we need to decide - do we want this migration? Additionally, I think it's reasonable to, if we want it, send both [1] and patch 27/28 as a follow up separate from the v1 non-RFC of the series. 5. Errata handling - the default already disallows SPE on the affected silicon, which seems right. I wonder whether kvm-arm.ignore_spe_errata should exist at all though, other than in some sort of debug mode. So 1 is a known dependency, I think there's no getting around that, and thus that makes merging [0] or something like it a top priority. It seems to me 2 is pretty clear-cut, and 4 can reasonably (if we want it) be sent as a follow up. So really 3 and 5 are the decisions to make here! -- Cheers, Lorenzo [0]: https://lore.kernel.org/all/20260714160411.302386-1-alexandru.elisei@arm.com/ [1]: https://lore.kernel.org/kvmarm/20260702142912.6395-1-alexandru.elisei@arm.com/