From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b="nXqb+Bzu" Received: from linux.microsoft.com (linux.microsoft.com [13.77.154.182]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id A5564D6E; Fri, 24 Nov 2023 03:05:02 -0800 (PST) Received: from [192.168.1.150] (181-28-144-85.ftth.glasoperator.nl [85.144.28.181]) by linux.microsoft.com (Postfix) with ESMTPSA id 3571420B74C0; Fri, 24 Nov 2023 03:04:58 -0800 (PST) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 3571420B74C0 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1700823902; bh=7jaZ0scpk4NByvTCBB0IHW+wWWfI9aApWVslFKRIx8s=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=nXqb+Bzu6O/7N3ZWRXOm99TsvtglFjoQqN8btxWl2cQbPDnKJ9cZzWM7WP7FHqaoT k88jeDK15/O683dzQsHAukzlISzzRMID+4EIwy7BaWmKrJ+F+3EoTZrXSwEEWi3mjh Up+Dq/LtF41FV+wluqOVtVWxCr9o5lgV1AbxcJe8= Message-ID: <58c82110-45b2-4e23-9a82-90e1f3fa43c2@linux.microsoft.com> Date: Fri, 24 Nov 2023 12:04:56 +0100 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 1/3] x86/tdx: Check for TDX partitioning during early TDX init Content-Language: en-US To: "Kirill A. Shutemov" Cc: linux-kernel@vger.kernel.org, Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Ingo Molnar , Michael Kelley , Nikolay Borisov , Peter Zijlstra , Thomas Gleixner , Tom Lendacky , x86@kernel.org, Dexuan Cui , linux-hyperv@vger.kernel.org, stefan.bader@canonical.com, tim.gardner@canonical.com, roxana.nicolescu@canonical.com, cascardo@canonical.com, kys@microsoft.com, haiyangz@microsoft.com, wei.liu@kernel.org, sashal@kernel.org, stable@vger.kernel.org References: <20231122170106.270266-1-jpiotrowski@linux.microsoft.com> <20231123135846.pakk44rqbbi7njmb@box.shutemov.name> <9f550947-9d13-479c-90c4-2e3f7674afee@linux.microsoft.com> <20231124104337.gjfyasjmo5pp666l@box.shutemov.name> From: Jeremi Piotrowski In-Reply-To: <20231124104337.gjfyasjmo5pp666l@box.shutemov.name> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 24/11/2023 11:43, Kirill A. Shutemov wrote: > On Fri, Nov 24, 2023 at 11:31:44AM +0100, Jeremi Piotrowski wrote: >> On 23/11/2023 14:58, Kirill A. Shutemov wrote: >>> On Wed, Nov 22, 2023 at 06:01:04PM +0100, Jeremi Piotrowski wrote: >>>> Check for additional CPUID bits to identify TDX guests running with Trust >>>> Domain (TD) partitioning enabled. TD partitioning is like nested virtualization >>>> inside the Trust Domain so there is a L1 TD VM(M) and there can be L2 TD VM(s). >>>> >>>> In this arrangement we are not guaranteed that the TDX_CPUID_LEAF_ID is visible >>>> to Linux running as an L2 TD VM. This is because a majority of TDX facilities >>>> are controlled by the L1 VMM and the L2 TDX guest needs to use TD partitioning >>>> aware mechanisms for what's left. So currently such guests do not have >>>> X86_FEATURE_TDX_GUEST set. >>>> >>>> We want the kernel to have X86_FEATURE_TDX_GUEST set for all TDX guests so we >>>> need to check these additional CPUID bits, but we skip further initialization >>>> in the function as we aren't guaranteed access to TDX module calls. >>> >>> I don't follow. The idea of partitioning is that L2 OS can be >>> unenlightened and have no idea if it runs indide of TD. But this patch >>> tries to enumerate TDX anyway. >>> >>> Why? >>> >> >> That's not the only idea of partitioning. Partitioning provides different privilege >> levels within the TD, and unenlightened L2 OS can be made to work but are inefficient. >> In our case Linux always runs enlightened (both with and without TD partitioning), and >> uses TDX functionality where applicable (TDX vmcalls, PTE encryption bit). > > What value L1 adds in this case? If L2 has to be enlightened just run the > enlightened OS directly as L1 and ditch half-measures. I think you can > gain some performance this way. > It's primarily about the privilege separation, performance is a reason one doesn't want to run unenlightened. The L1 makes the following possible: - TPM emulation within the trust domain but isolated from the OS - infrastructure interfaces for things like VM live migration - support for Virtual Trust Levels[1], Virtual Secure Mode[2] These provide a lot of value to users, it's not at all about half-measures. [1]: https://lore.kernel.org/lkml/1681192532-15460-1-git-send-email-ssengar@linux.microsoft.com/ [2]: https://lore.kernel.org/lkml/20231108111806.92604-1-nsaenz@amazon.com/