From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3C660C433EF for ; Mon, 27 Jun 2022 16:34:08 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id AB27E8E0002; Mon, 27 Jun 2022 12:34:07 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A62588E0001; Mon, 27 Jun 2022 12:34:07 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 929D28E0002; Mon, 27 Jun 2022 12:34:07 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 80E5B8E0001 for ; Mon, 27 Jun 2022 12:34:07 -0400 (EDT) Received: from smtpin22.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay11.hostedemail.com (Postfix) with ESMTP id 4A2F880826 for ; Mon, 27 Jun 2022 16:34:07 +0000 (UTC) X-FDA: 79624562934.22.0FCD6E8 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by imf08.hostedemail.com (Postfix) with ESMTP id 58D78160031 for ; Mon, 27 Jun 2022 16:34:06 +0000 (UTC) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 4C92460EA0 for ; Mon, 27 Jun 2022 16:34:05 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 721EFC341D4 for ; Mon, 27 Jun 2022 16:34:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1656347643; bh=/SrPj904ouZSQFbqV4kyfH3imhY4twalKi5RBsFEDXg=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=hOiOupAlz0TGohr1zjOI5lFppGqzRMTEsnXwUTjo+AoOMM6Gpog71SfivxPwIX7NV iXB4scHnRb8F21nU9UWDw3UJPTycIN4itNmgWilRZJoxPN/ykb4KNUwBCASRz2g8B5 ozEcRcl0G9O6t24gpWsacxQyuRb82ttrYlvzpT5chxphOl/fxEh/ZzLG6Iwp5yyJBa I6G7FBcxCOwrsgR4to3Kezu+lQsavJbnz+NbIJG4Iin/YGpbkXyITEBWjaEAY7wjGG zm3V3Dpkg2/z1CzyK/M+yUiv7tHtUQTptE2M+6o50uuxDkrnO+NPnVCHt0JoBNBozO Fy8qOM9M2nZGg== Received: by mail-oi1-f173.google.com with SMTP id e131so13506668oif.13 for ; Mon, 27 Jun 2022 09:34:03 -0700 (PDT) X-Gm-Message-State: AJIora/YihsfXAA+Xwj7r7poXngt2M1wj8B3/Afa/b/73udrxtvqlx2u VRCeoKVrjjMIhFHuiMNtR1Z78r8tCKs57BwAI4Q= X-Google-Smtp-Source: AGRyM1vx0evnQKAh1ZRdKNDvgSVxe65OJG5sTTVLkDoO84Dm1BfKlU9Oq5kS74fbNmzzvJd58LGrRlW4KWp06rIXVKM= X-Received: by 2002:a05:6808:300e:b0:32c:425e:df34 with SMTP id ay14-20020a056808300e00b0032c425edf34mr8224110oib.126.1656347642388; Mon, 27 Jun 2022 09:34:02 -0700 (PDT) MIME-Version: 1.0 References: <20220614120231.48165-1-kirill.shutemov@linux.intel.com> <20220627113019.3q62luiay7izhehr@black.fi.intel.com> <20220627122230.7eetepoufd5w3lxd@black.fi.intel.com> In-Reply-To: From: Ard Biesheuvel Date: Mon, 27 Jun 2022 18:33:51 +0200 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCHv7 00/14] mm, x86/cc: Implement support for unaccepted memory To: Peter Gonda Cc: "Kirill A. Shutemov" , Borislav Petkov , Andy Lutomirski , Sean Christopherson , Andrew Morton , Joerg Roedel , Andi Kleen , Kuppuswamy Sathyanarayanan , David Rientjes , Vlastimil Babka , Tom Lendacky , Thomas Gleixner , Peter Zijlstra , Paolo Bonzini , Ingo Molnar , Varad Gautam , Dario Faggioli , Dave Hansen , Mike Rapoport , David Hildenbrand , Marcelo Cerri , tim.gardner@canonical.com, Khalid ElMously , philip.cox@canonical.com, "the arch/x86 maintainers" , Linux Memory Management List , linux-coco@lists.linux.dev, linux-efi , LKML Content-Type: text/plain; charset="UTF-8" ARC-Authentication-Results: i=1; imf08.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=hOiOupAl; dmarc=pass (policy=none) header.from=kernel.org; spf=pass (imf08.hostedemail.com: domain of ardb@kernel.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=ardb@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1656347646; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=/SrPj904ouZSQFbqV4kyfH3imhY4twalKi5RBsFEDXg=; b=ZQKe0AJVWsWaitJPpUJDjFJxrEgP1hTragnp/djUKlq5/l9GnVaOQBVFnz6SDV7hbkBUg8 cZldWCOIr3SCv0svfxstCDreTcQMnnbkhhFjLjbLLbjwq0ifTj9NC6wKktvp1Qj05Z5qzz iBdL7jAgQFZjw5REJSaf+7JxiLW9mGk= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1656347646; a=rsa-sha256; cv=none; b=O/gKEqOr3g8Cj9YkOBags5lbubXV0bdp0PZzO9pJKkyWolvtCcFN/OlpnZAcn9w7pHRp3j Bp4gRFaCbRdj3M/3AA8ACULnHy23ouZ9Kfqtfhk+anSn5XbaSfzzgiDk6mdS7OcWL5AV7z KYoZqivwKpo9ujh6YaNFdduRRV7dt1w= X-Stat-Signature: hggthhftetbihku94gmycc3n6se8a6xo X-Rspamd-Queue-Id: 58D78160031 X-Rspam-User: Authentication-Results: imf08.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=hOiOupAl; dmarc=pass (policy=none) header.from=kernel.org; spf=pass (imf08.hostedemail.com: domain of ardb@kernel.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=ardb@kernel.org X-Rspamd-Server: rspam12 X-HE-Tag: 1656347646-329413 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, 27 Jun 2022 at 18:17, Peter Gonda wrote: > > On Mon, Jun 27, 2022 at 6:22 AM Kirill A. Shutemov > wrote: > > > > On Mon, Jun 27, 2022 at 01:54:45PM +0200, Ard Biesheuvel wrote: > > > On Mon, 27 Jun 2022 at 13:30, Kirill A. Shutemov > > > wrote: > > > > > > > > On Fri, Jun 24, 2022 at 10:37:10AM -0600, Peter Gonda wrote: > > > > > On Tue, Jun 14, 2022 at 6:03 AM Kirill A. Shutemov > > > > > wrote: > > > > > > > > > > > > UEFI Specification version 2.9 introduces the concept of memory > > > > > > acceptance: some Virtual Machine platforms, such as Intel TDX or AMD > > > > > > SEV-SNP, requiring memory to be accepted before it can be used by the > > > > > > guest. Accepting happens via a protocol specific for the Virtual > > > > > > Machine platform. > > > > > > > > > > > > Accepting memory is costly and it makes VMM allocate memory for the > > > > > > accepted guest physical address range. It's better to postpone memory > > > > > > acceptance until memory is needed. It lowers boot time and reduces > > > > > > memory overhead. > > > > > > > > > > > > The kernel needs to know what memory has been accepted. Firmware > > > > > > communicates this information via memory map: a new memory type -- > > > > > > EFI_UNACCEPTED_MEMORY -- indicates such memory. > > > > > > > > > > > > Range-based tracking works fine for firmware, but it gets bulky for > > > > > > the kernel: e820 has to be modified on every page acceptance. It leads > > > > > > to table fragmentation, but there's a limited number of entries in the > > > > > > e820 table > > > > > > > > > > > > Another option is to mark such memory as usable in e820 and track if the > > > > > > range has been accepted in a bitmap. One bit in the bitmap represents > > > > > > 2MiB in the address space: one 4k page is enough to track 64GiB or > > > > > > physical address space. > > > > > > > > > > > > In the worst-case scenario -- a huge hole in the middle of the > > > > > > address space -- It needs 256MiB to handle 4PiB of the address > > > > > > space. > > > > > > > > > > > > Any unaccepted memory that is not aligned to 2M gets accepted upfront. > > > > > > > > > > > > The approach lowers boot time substantially. Boot to shell is ~2.5x > > > > > > faster for 4G TDX VM and ~4x faster for 64G. > > > > > > > > > > > > TDX-specific code isolated from the core of unaccepted memory support. It > > > > > > supposed to help to plug-in different implementation of unaccepted memory > > > > > > such as SEV-SNP. > > > > > > > > > > > > The tree can be found here: > > > > > > > > > > > > https://github.com/intel/tdx.git guest-unaccepted-memory > > > > > > > > > > Hi Kirill, > > > > > > > > > > I have a couple questions about this feature mainly about how cloud > > > > > customers can use this, I assume since this is a confidential compute > > > > > feature a large number of the users of these patches will be cloud > > > > > customers using TDX and SNP. One issue I see with these patches is how > > > > > do we as a cloud provider know whether a customer's linux image > > > > > supports this feature, if the image doesn't have these patches UEFI > > > > > needs to fully validate the memory, if the image does we can use this > > > > > new protocol. In GCE we supply our VMs with a version of the EDK2 FW > > > > > and the customer doesn't input into which UEFI we run, as far as I can > > > > > tell from the Azure SNP VM documentation it seems very similar. We > > > > > need to somehow tell our UEFI in the VM what to do based on the image. > > > > > The current way I can see to solve this issue would be to have our > > > > > customers give us metadata about their VM's image but this seems kinda > > > > > burdensome on our customers (I assume we'll have more features which > > > > > both UEFI and kernel need to both support inorder to be turned on like > > > > > this one) and error-prone, if a customer incorrectly labels their > > > > > image it may fail to boot.. Has there been any discussion about how to > > > > > solve this? My naive thoughts were what if UEFI and Kernel had some > > > > > sort of feature negotiation. Maybe that could happen via an extension > > > > > to exit boot services or a UEFI runtime driver, I'm not sure what's > > > > > best here just some ideas. > > > > > > > > Just as an idea, we can put info into UTS_VERSION which can be read from > > > > the built bzImage. We have info on SMP and preeption there already. > > > > > > > > > > Instead of hacking this into the binary, couldn't we define a protocol > > > that the kernel will call from the EFI stub (before EBS()) to identify > > > itself as an image that understands unaccepted memory, and knows how > > > to deal with it? > > > > > > That way, the firmware can accept all the memory on behalf of the OS > > > at ExitBootServices() time, unless the OS has indicated there is no > > > need to do so. > > > > I agree it would be better. But I think it would require change to EFI > > spec, no? > > Could this somehow be amended on to the UEFI Specification version 2.9 > change which added all of the unaccepted memory features? > Why would this need a change in the EFI spec? Not every EFI protocol needs to be in the spec.