From: Jeremi Piotrowski <jpiotrowski@linux.microsoft.com>
To: "Huang, Kai" <kai.huang@intel.com>,
"kirill.shutemov@linux.intel.com"
<kirill.shutemov@linux.intel.com>,
"mhkelley58@gmail.com" <mhkelley58@gmail.com>,
"Cui, Dexuan" <decui@microsoft.com>,
"Reshetova, Elena" <elena.reshetova@intel.com>,
Borislav Petkov <bp@alien8.de>
Cc: "cascardo@canonical.com" <cascardo@canonical.com>,
"tim.gardner@canonical.com" <tim.gardner@canonical.com>,
"dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
"thomas.lendacky@amd.com" <thomas.lendacky@amd.com>,
"roxana.nicolescu@canonical.com" <roxana.nicolescu@canonical.com>,
"stable@vger.kernel.org" <stable@vger.kernel.org>,
"haiyangz@microsoft.com" <haiyangz@microsoft.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"mingo@redhat.com" <mingo@redhat.com>,
"kys@microsoft.com" <kys@microsoft.com>,
"stefan.bader@canonical.com" <stefan.bader@canonical.com>,
"nik.borisov@suse.com" <nik.borisov@suse.com>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"hpa@zytor.com" <hpa@zytor.com>,
"peterz@infradead.org" <peterz@infradead.org>,
"wei.liu@kernel.org" <wei.liu@kernel.org>,
"sashal@kernel.org" <sashal@kernel.org>,
"linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
"bp@alien8.de" <bp@alien8.de>, "x86@kernel.org" <x86@kernel.org>
Subject: Re: [PATCH v1 1/3] x86/tdx: Check for TDX partitioning during early TDX init
Date: Thu, 7 Dec 2023 20:35:33 +0100 [thread overview]
Message-ID: <6ec6b73e-c3f6-4952-9835-0dbc4b7c199f@linux.microsoft.com> (raw)
In-Reply-To: <8362bf44-f933-4a7e-9e56-a7c425a2ba5a@linux.microsoft.com>
On 07/12/2023 18:21, Jeremi Piotrowski wrote:
> On 07/12/2023 13:58, Huang, Kai wrote:
>>>
>>> That's how it currently works - all the enlightenments are in hypervisor/paravisor
>>> specific code in arch/x86/hyperv and drivers/hv and the vm is not marked with
>>> X86_FEATURE_TDX_GUEST.
>>
>> And I believe there's a reason that the VM is not marked as TDX guest.
> Yes, as Elena said:
> """
> OK, so in your case it is a decision of L1 VMM not to set the TDX_CPUID_LEAF_ID
> to reflect that it is a tdx guest and it is on purpose because you want to
> drop into a special tdx guest, i.e. partitioned guest.
> """
> TDX does not provide a means to let the partitioned guest know that it needs to
> cooperate with the paravisor (e.g. because TDVMCALLs are routed to L0) so this is
> exposed in a paravisor specific way (cpuids in patch 1).
>
>>
>>>
>>> But without X86_FEATURE_TDX_GUEST userspace has no unified way to discover that an
>>> environment is protected by TDX and also the VM gets classified as "AMD SEV" in dmesg.
>>> This is due to CC_ATTR_GUEST_MEM_ENCRYPT being set but X86_FEATURE_TDX_GUEST not.
>>
>> Can you provide more information about what does _userspace_ do here?
>
> I gave one usecase in a different email. A workload scheduler like Kubernetes might want to
> place a workload in a confidential environment, and needs a way to determine that a VM is
> TDX protected (or SNP protected) to make that placement decision.
>
>>
>> What's the difference if it sees a TDX guest or a normal non-coco guest in
>> /proc/cpuinfo?
>>
>> Looks the whole purpose of this series is to make userspace happy by advertising
>> TDX guest to /proc/cpuinfo. But if we do that we will have bad side-effect in
>> the kernel so that we need to do things in your patch 2/3.
>>
>
> Yes, exactly. It's unifying the two approaches so that userspace doesn't have to
> care.
>
>> That doesn't seem very convincing.
>
> Why not?
> The whole point of the kernel is to provide a unified interface to userspace and
> abstract away these small differences. Yes it requires some kernel code to do,
> thats not a reason to force every userspace to implement its own logic. This is
> what the flags in /proc/cpuinfo are for.
>
So I feel like we're finally getting to the gist of the disagreements in this thread.
Here's something I think we should all agree on (both a) and b)). X86_FEATURE_TDX_GUEST:
a) is visible to userspace and not just some kernel-only construct
b) means "this is a guest running in an Intel TDX Trust Domain, and said guest is aware
of TDX"
a) is obvious but I think needs restating. b) is what userspace expects, and excludes legacy
(/unmodified) guests running in a TD. That's a reasonable definition.
For kernel only checks we can rely on platform-specific CC_ATTRS checked through
intel_cc_platform_has.
@Borislav: does that sound reasonable to you?
@Kai, @Kirill, @Elena: can I get you to agree with this compromise, for userspace' sake?
Jeremi
next prev parent reply other threads:[~2023-12-07 19:35 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-22 17:01 [PATCH v1 1/3] x86/tdx: Check for TDX partitioning during early TDX init Jeremi Piotrowski
2023-11-22 17:01 ` [PATCH v1 2/3] x86/coco: Disable TDX module calls when TD partitioning is active Jeremi Piotrowski
2023-11-23 14:13 ` Kirill A. Shutemov
2023-11-24 10:38 ` Jeremi Piotrowski
2023-11-29 10:37 ` Huang, Kai
2023-12-01 15:27 ` Jeremi Piotrowski
2023-11-22 17:01 ` [PATCH v1 3/3] x86/tdx: Provide stub tdx_accept_memory() for non-TDX configs Jeremi Piotrowski
2023-11-23 14:11 ` Kirill A. Shutemov
2023-11-24 10:00 ` Jeremi Piotrowski
2023-11-22 17:19 ` [PATCH v1 1/3] x86/tdx: Check for TDX partitioning during early TDX init Jeremi Piotrowski
2023-11-29 16:40 ` Borislav Petkov
2023-11-30 7:08 ` Reshetova, Elena
2023-11-30 7:55 ` Borislav Petkov
2023-11-30 8:31 ` Reshetova, Elena
2023-11-30 9:21 ` Borislav Petkov
2023-12-04 16:44 ` Jeremi Piotrowski
2023-12-04 13:39 ` Jeremi Piotrowski
2023-12-04 19:37 ` Jeremi Piotrowski
2023-11-23 13:58 ` Kirill A. Shutemov
2023-11-24 10:31 ` Jeremi Piotrowski
2023-11-24 10:43 ` Kirill A. Shutemov
2023-11-24 11:04 ` Jeremi Piotrowski
2023-11-24 13:33 ` Kirill A. Shutemov
2023-11-24 16:19 ` Jeremi Piotrowski
2023-11-29 4:36 ` Huang, Kai
2023-12-01 16:16 ` Jeremi Piotrowski
2023-12-05 13:26 ` Huang, Kai
2023-12-06 18:47 ` Jeremi Piotrowski
2023-12-07 12:58 ` Huang, Kai
2023-12-07 17:21 ` Jeremi Piotrowski
2023-12-07 19:35 ` Jeremi Piotrowski [this message]
2023-12-08 10:51 ` Huang, Kai
2023-12-07 17:36 ` Reshetova, Elena
2023-12-08 12:45 ` Jeremi Piotrowski
2023-12-04 9:17 ` Reshetova, Elena
2023-12-04 19:07 ` Jeremi Piotrowski
2023-12-05 10:54 ` Kirill A. Shutemov
2023-12-06 17:49 ` Jeremi Piotrowski
2023-12-06 22:54 ` Kirill A. Shutemov
2023-12-07 17:06 ` Jeremi Piotrowski
2023-12-07 20:56 ` Kirill A. Shutemov
2023-12-05 13:24 ` Reshetova, Elena
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