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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6C868C4332F for ; Mon, 9 May 2022 22:18:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231470AbiEIWV5 (ORCPT ); Mon, 9 May 2022 18:21:57 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59156 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229510AbiEIWVy (ORCPT ); Mon, 9 May 2022 18:21:54 -0400 Received: from mail.skyhub.de (mail.skyhub.de [IPv6:2a01:4f8:190:11c2::b:1457]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3537A26BC9A; Mon, 9 May 2022 15:17:59 -0700 (PDT) Received: from zn.tnic (p5de8eeb4.dip0.t-ipconnect.de [93.232.238.180]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id 44E961EC0505; Tue, 10 May 2022 00:17:53 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1652134673; 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: content-transfer-encoding:in-reply-to:in-reply-to: references:references; bh=2k2dEWW2F1hrc51g6pFhQEncF54Nbue4YVbgz5LkyTE=; b=lV/tv/BBA10J6KuReciOQ9eOK4caCe95n4wYgIVJjxAnm/MvUQV1MMl/fvLSanKq3O8I+h /WI2c8ufp0ts8T7FBmUQza5KOUUZx8AwJj4xvAqNH45y8lo3IFnbxg40+yVgxqBY0F2wls fezDy9Tqdv9Nm71Pao3DSOnHh2SHL4Q= Date: Tue, 10 May 2022 00:17:56 +0200 From: Borislav Petkov To: Dave Hansen Cc: Dan Williams , Martin Fernandez , Linux Kernel Mailing List , linux-efi , platform-driver-x86@vger.kernel.org, Linux MM , "H. Peter Anvin" , daniel.gutson@eclypsium.com, Darren Hart , Andy Shevchenko , Kees Cook , Andrew Morton , Ard Biesheuvel , Ingo Molnar , Thomas Gleixner , Dave Hansen , "Rafael J. Wysocki" , X86 ML , "Schofield, Alison" , hughsient@gmail.com, alex.bazhaniuk@eclypsium.com, Greg KH , Mike Rapoport , Ben Widawsky , "Huang, Kai" , Sean Christopherson , "Shutemov, Kirill" , Kuppuswamy Sathyanarayanan , Tom Lendacky , Michael Roth Subject: Re: [PATCH v8 0/8] x86: Show in sysfs if a memory node is able to do encryption Message-ID: References: <6d90c832-af4a-7ed6-4f72-dae08bb69c37@intel.com> <47140A56-D3F8-4292-B355-5F92E3BA9F67@alien8.de> <6abea873-52a2-f506-b21b-4b567bee1874@intel.com> <4bc56567-e2ce-40ec-19ab-349c8de8d969@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 09, 2022 at 11:47:43AM -0700, Dave Hansen wrote: > ... adding some KVM/TDX folks + AMD SEV folks as they're going to probably need something like that too. > On 5/6/22 12:02, Boris Petkov wrote: > >> This node attribute punts the problem back out to userspace. It > >> gives userspace the ability to steer allocations to compatible NUMA > >> nodes. If something goes wrong, they can use other NUMA ABIs to > >> inspect the situation, like /proc/$pid/numa_maps. > > That's all fine and dandy but I still don't see the *actual*, > > real-life use case of why something would request memory of > > particular encryption capabilities. Don't get me wrong - I'm not > > saying there are not such use cases - I'm saying we should go all the > > way and fully define properly *why* we're doing this whole hoopla. > > Let's say TDX is running on a system with mixed encryption > capabilities*. Some NUMA nodes support TDX and some don't. If that > happens, your guest RAM can come from anywhere. When the host kernel > calls into the TDX module to add pages to the guest (via > TDH.MEM.PAGE.ADD) it might get an error back from the TDX module. At > that point, the host kernel is stuck. It's got a partially created > guest and no recourse to fix the error. Thanks for that detailed use case, btw! > This new ABI provides a way to avoid that situation in the first place. > Userspace can look at sysfs to figure out which NUMA nodes support > "encryption" (aka. TDX) and can use the existing NUMA policy ABI to > avoid TDH.MEM.PAGE.ADD failures. > > So, here's the question for the TDX folks: are these mixed-capability > systems a problem for you? Does this ABI help you fix the problem? What I'm not really sure too is, is per-node granularity ok? I guess it is but let me ask it anyway... > Will your userspace (qemu and friends) actually use consume from this ABI? Same question for SEV folks - do you guys think this interface would make sense for the SEV side of things? > * There are three ways we might hit a system with this issue: > 1. NVDIMMs that don't support TDX, like lack of memory integrity > protection. > 2. CXL-attached memory controllers that can't do encryption at all > 3. Nominally TDX-compatible memory that was not covered/converted by > the kernel for some reason (memory hot-add, or ran out of TDMR > resources) And I think some of those might be of interest to the AMD side of things too. Thx. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette