From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 2F8673BF68F; Wed, 26 Aug 2026 11:36:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787744181; cv=none; b=szMJt/KH19TrxpcBVltDMiNF8Lg2P3rpxlMm/6rLgj4/9H6QJuCYBYpBgaI0iHrOOOyD7EJOI3+SsU4AA1x06YQ/Rg9RuzyeJI8F/9Yl+7p+ePdalyfjS9j/ZPvLsJLOe7puD3w+vJL+dn5rdEDVL+ll20JL4Ufz2cxdwIkkoRs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787744181; c=relaxed/simple; bh=c0cU0JM9kk6THE4lwS7F3hZKvFcmoejPQkRkBMB2YEY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=p8yBGxVRkSSQIE3eoyN5h9ClZVb2gbFa6d1RZK0DRUGaqr8+aTEAUDIZpAkKbapKeVyGPyafHY/COXZ3ZdC+C7T9tUOk2jhjfCGuNO486UVOdZCl1f3qm8f7nzRmUy0+NezGnR37d8dZec6UaUx3RUwzCFa9NuEPVju5iFygvYI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=FDonw4av; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="FDonw4av" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 015511F000E9; Wed, 26 Aug 2026 11:36:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787744180; bh=1c7VcxPCAWwjhajO6j7AGFWsss4LLP8nxJ4e84M39nE=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=FDonw4avUZLdVWPH4NlSKp00RUrlZnjRSlkj5qSYSaOqmpH4XnP/1GuiTxPBzvNIU dK9TU04K8qiuEY9j4b2Y6FwZ2TYEnK3WAhpykoGck0nwB3B36oBIUxvQhd3elDzc3D ma59CaC5EsVADAf7iPTnEBIFyRRcic6+z78/Kz92MVWeSzEDc8tjjCZUZ0hQE/u0sQ jYii0BJhb+izLN2vbdGlyQOQja4JZYFA2CKuwN+NbGZqD76Ymm+fw0giF/JKaKfStr ySfWORrszMDbJDqMOUQOhcA4gtmbG2pXpfDCqV3csdBGntoJBaw+FmHib5jhzIR6Nz WPBx/RghU3ePA== Message-ID: <5921ace1-219d-4947-99d9-13b56e1ec6fa@kernel.org> Date: Wed, 26 Aug 2026 13:36:12 +0200 Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFCv2 PATCH 0/6] Support memory hotplug/unplug for TDX CoCo guests To: Zhenzhong Duan , marcandre.lureau@redhat.com, kas@kernel.org, rick.p.edgecombe@intel.com, prsampat@amd.com, pbonzini@redhat.com, mst@redhat.com, peterx@redhat.com, chenyi.qiang@intel.com, elena.reshetova@intel.com, michael.roth@amd.com, ackerleytng@google.com Cc: linux-kernel@vger.kernel.org, linux-coco@lists.linux.dev, virtualization@lists.linux.dev, x86@kernel.org, yilun.xu@intel.com, xiaoyao.li@intel.com, chao.p.peng@intel.com References: <20260623101739.79695-1-zhenzhong.duan@intel.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit On 6/23/26 12:17, Zhenzhong Duan wrote: > This RFCv2 series implements comprehensive support for virtio-mem and ACPI > DIMM memory hotplug/unplug in Intel TDX confidential computing guests. > It explores the start-private memory approach utilizing the native > TDG.MEM.PAGE.RELEASE API. > > We are seeking feedback from Kiryl on the CoCo guest implementation, MM > experts on DIMM & virio-mem memory hotplug integration and broader > virtio/CoCo community input on the overall approach. We are not seeking > x86 maintainer review at this stage. > > == Changes from RFC v1 == > > - Eliminated callback infrastructure: Dropped plug callback and replaced > unplug callback with platform-level unaccept function into core MM > hotplug and virtio-mem subsystems. > - Added comprehensive bitmap tracking: Introduced a "plugged" bitmap > alongside the unaccepted bitmap to track populated hotplug memory > states to support load_unaligned_zeropad(). > - Enhanced SRAT parsing: Extended the EFI stub to parse ACPI SRAT tables > early, ensuring hotpluggable ranges are tracked from initial boot. > > For more introduction about the background or other efforts in community, > please check the RFCv1 cover letter [1]. > > == Technical Approach == > > - Early SRAT Integration: A lightweight EFI stub parser scans ACPI SRAT > tables to identify hotpluggable ranges and adjust bitmap boundaries > early, avoiding the overhead of the full ACPI subsystem. > - Comprehensive Bitmap Tracking: Introduces a "plugged" bitmap right > after the unaccepted bitmap. Both static and hotplugged memory are > tracked, allowing the guest to map which ranges are populated by the > VMM. This prevents acceptance beyond plugged memory boundaries due to > load_unaligned_zeropad() operations. > - Platform Extensibility: Exposes generic CoCo memory interfaces. Other > confidential platforms (like AMD SEV-SNP) can easily adopt this by > hooking their specific mechanisms into arch_unaccept_memory(). > - Hotplug & Guest Control: Integrates platform-level unaccept logic > into ACPI hotplug and virtio-mem handlers. Uses TDG.MEM.PAGE.RELEASE > for TDX to explicitly set memory to the "unaccepted" state during > unplug, removing host hole-punching dependencies. > - Kexec Handover: Leverages existing EFI mechanisms to seamlessly hand > over both the extended unaccepted bitmap and the new plugged bitmap > across kexec boundaries. > > == Testing == > > - dimm and virtio-mem memory hotplug/unplug > - lazy and eager accept > - kexec/kdump with hotplugged memory > > This is tested with Marc-André Lureau's newest qemu series [2] What's the status of this? I am still not sure whether we shouldn't perform acceptance from move_pfn_range_to_zone() and from memory notifiers / generic_online_page. In particular, it's unclear to me how virtio-mem (which uses interfaces to add/remove memory) interacts with unaccept_memory / coco bitmap. Can we have an overall design view on what happens at which stage when adding / removing memory through virtio-mem? -- Cheers, David