From: Sathyanarayanan Kuppuswamy <sathyanarayanan.kuppuswamy@linux.intel.com>
To: Kai Huang <kai.huang@intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org
Cc: "H . Peter Anvin" <hpa@zytor.com>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
Tony Luck <tony.luck@intel.com>, Andi Kleen <ak@linux.intel.com>,
Wander Lairson Costa <wander@redhat.com>,
Isaku Yamahata <isaku.yamahata@gmail.com>,
marcelo.cerri@canonical.com, tim.gardner@canonical.com,
khalid.elmously@canonical.com, philip.cox@canonical.com,
linux-kernel@vger.kernel.org, "Nakajima,
Jun" <jun.nakajima@intel.com>,
"Yao, Jiewen" <jiewen.yao@intel.com>
Subject: Re: [PATCH v8 2/5] x86/tdx: Add TDX Guest event notify interrupt support
Date: Fri, 24 Jun 2022 15:23:18 -0700 [thread overview]
Message-ID: <7ccfa470-ead3-220d-a354-de7e509adb08@linux.intel.com> (raw)
In-Reply-To: <efb2cdab-289b-8757-fe5e-5348519b0474@linux.intel.com>
+ Jiewen
Jiewen, Can you please comment on the specification related queries?
On 6/20/22 8:44 AM, Sathyanarayanan Kuppuswamy wrote:
> Hi,
>
> + Jun
>
> On 6/20/22 5:33 AM, Kai Huang wrote:
>> On Wed, 2022-06-08 at 19:52 -0700, Kuppuswamy Sathyanarayanan wrote:
>>> Host-guest event notification via configured interrupt vector is useful
>>> in cases where a guest makes an asynchronous request and needs a
>>> callback from the host to indicate the completion or to let the host
>>> notify the guest about events like device removal. One usage example is,
>>> callback requirement of GetQuote asynchronous hypercall.
>>
>> Although this paragraph is from GHCI spec, IMHO it is not very helpful. In
>> fact, I think this paragraph is not that right and should be removed from GHCI.
>> The reason is such event notification from VMM in cases like "device removal" is
>> too vague. There's no _specification_ in GHCI around which "device removal"
>> should VMM inject such event. For instance, I _think_ the Qemu enumerated ACPI-
>> based hotplug should continue to work in TD.
>
> Yes. It just says that it *can* be used to signal a device removal. It is just
> an example for where it can be used. But I agree that such a use case is vague.
> If it makes it better, I am fine with removing it.
>
> Copied from sec 3.5 TDG.VP.VMCALL<SetupEventNotifyInterrupt>:
>
> "Example of an operation that can use the event notify is the host
> VMM signaling a device removal to the TD, in response to which a TD may
> unload a device driver."
>
>>
>> That being said, if a TD has multiple devices, it cannot know whether the VMM
>> will inject the removal event via the vector set by SetupEventNotifyInterrupt.
>> And for the same device in the same TD, different VMMs may use different way to
>> notify its removal.
>
> As per current design, If it is used for device removal, I think all registered
> device drivers will get the notification and the individual device driver has
> to check whether it is applicable for them.
>
> If the SetupEventNotifyInterrupt TDVMCALL specification is extended to specify
> the exact device or use case detail, then it can optimize the implementation.
>
>>
>> It seems GetQuote is the only user of SetupEventNotifyInterrupt. Maybe we
>> should just declare it is for GetQuote.
>
> Ok.
>
>>
>> Isaku, what do you think? Does this make sense?
>>
>>>
>>> In TDX guest, SetupEventNotifyInterrupt hypercall can be used by the
>>> guest to specify which interrupt vector to use as an event-notify
>>> vector to the VMM. Details about the SetupEventNotifyInterrupt
>>> hypercall can be found in TDX Guest-Host Communication Interface
>>> (GHCI) Specification, sec 3.5 "VP.VMCALL<SetupEventNotifyInterrupt>".
>>> Add a tdx_hcall_set_notify_intr() helper function to implement the
>>> SetupEventNotifyInterrupt hypercall.
>>
>> As you also used "can" above, the GHCI only says the VMM _CAN_ inject the vector
>> set by SetupEventNotifyInterrupt, but not must (3.3 TDG.VP.VMCALL<GetQuote>).
>> This means theoretically TD should implement pooling mode in case VMM doesn't
>> support injecting event via vector done by SetupEventNotifyInterrupt?
>
> Yes. But GetQuote specification does not talk about the pooling mode
> use case as well. So I think it is just a wording confusion.
>
>>
>> Perhaps we should update the GHCI spec to use must..
>
> Ok.
>
>>
>>>
>>> Reserve 0xec IRQ vector address for TDX guest to receive the event
>>> completion notification from VMM. Also add related IDT handler to
>>> process the notification event.
>>
>> Here lacks why we need to choose to reserve a system vector. For instance, why
>> we cannot choose to use device IRQ way which only requires one vector on one
>
> As you have explained below, as per current spec, it just expects a system
> vector.
>
>> cpu. As you can see reserving a system vector isn't ideal especially for
>> attestation as it is not a frequent operation. It is wasteful of using IRQ
>
> I agree that event notification is currently only used for attestation. But I
> think in future there could be other use cases for it. If the intention is just
> to use it for attestation, then we can just modify the GetQuote TDVMCALL to pass
> the vector address, and there is no need for new TDVMCALL. I think the intention
> here is to have generic method for VMM to notify TD about some events. I am not
> clear about the possible future use cases, so I cannot comment on frequency of
> its use.
>
> Jun, any comments?
>
>
>
>> resource especially on server systems with a lot of CPUs.
>
> FWIW, this reservation is protected with CONFIG_INTEL_TDX_GUEST. So it will be
> reserved only for TDX use case.
>
>
>>
>> The reason is SetupEventNotifyInterrupt TDVMCALL only has one argument, which is
>> vector, but cannot specify which CPU that the VMM should inject the event to.
>> The GHCI spec doesn't say which CPU the VMM should inject to (i.e. must inject
>> to the CPU on which SetupEventNotifyInterrupt is called), so we can only assume
>> VMM can inject to any CPU.
>>
>> Btw, x86 maintainers,
>>
>> I'd like to check with you to see whether we should improve the existing
>> SetupEventNotifyInterrupt so we can choose to use request_irq() style for
>> attestation. Using request_irq() means we don't need to reserve a system
>> vector, but can allocate a vector dynamically when needed.
>>
>> Assuming we update SetupEventNotifyInterrupt to also allow TD to specify which
>> CPU (i.e. via APICID) to inject (along with the vector), my understanding is we
>> can use below way (idea only) to dynamically allocate a vector on one CPU when
>> attestation is needed:
>>
>>
>> int cpu, vector;
>> int irq;
>>
>> // request an IRQ, and prevent it from being migrated
>> irq = __irq_domain_alloc_irqs(x86_vector_domain, 0, 1, ...);
>> request_irq(irq, ...);
>>
>> // get vector, cpu from irq
>>
>> TDVMCALL<SetupEventNotifyInterrupt>(vector,
>> apic->cpu_present_to_apidid(cpu));
>>
>> Is this reasonable? If yes, is it worth to do?
>>
>
--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer
next prev parent reply other threads:[~2022-06-24 22:23 UTC|newest]
Thread overview: 77+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-09 2:52 [PATCH v8 0/5] Add TDX Guest Attestation support Kuppuswamy Sathyanarayanan
2022-06-09 2:52 ` [PATCH v8 1/5] x86/tdx: Add TDX Guest attestation interface driver Kuppuswamy Sathyanarayanan
2022-06-24 16:51 ` Dave Hansen
2022-06-27 14:50 ` Sathyanarayanan Kuppuswamy
2022-06-27 17:24 ` Dave Hansen
2022-06-30 23:50 ` Sathyanarayanan Kuppuswamy
2022-07-05 12:07 ` Kai Huang
2022-07-05 18:45 ` Sathyanarayanan Kuppuswamy
2022-07-05 18:52 ` Dave Hansen
2022-07-05 21:21 ` Sathyanarayanan Kuppuswamy
2022-07-05 22:31 ` Kai Huang
2022-07-06 22:27 ` Sathyanarayanan Kuppuswamy
2022-07-06 22:59 ` Kai Huang
2022-07-18 22:52 ` Sathyanarayanan Kuppuswamy
2022-06-09 2:52 ` [PATCH v8 2/5] x86/tdx: Add TDX Guest event notify interrupt support Kuppuswamy Sathyanarayanan
2022-06-20 12:33 ` Kai Huang
2022-06-20 15:44 ` Sathyanarayanan Kuppuswamy
2022-06-23 9:46 ` Kai Huang
2022-06-23 10:24 ` Kai Huang
2022-06-24 22:23 ` Sathyanarayanan Kuppuswamy [this message]
2022-06-24 23:41 ` Nakajima, Jun
2022-06-25 3:35 ` Yao, Jiewen
2022-06-27 11:21 ` Kai Huang
2022-06-27 14:56 ` Sathyanarayanan Kuppuswamy
2022-07-14 0:46 ` Sathyanarayanan Kuppuswamy
2022-07-14 10:42 ` Kai Huang
2022-07-14 20:55 ` Sathyanarayanan Kuppuswamy
2022-07-14 23:58 ` Kai Huang
2022-06-09 2:52 ` [PATCH v8 3/5] x86/mm: Make tdx_enc_status_changed() vmalloc address compatible Kuppuswamy Sathyanarayanan
2022-06-09 2:52 ` [PATCH v8 4/5] x86/mm: Add noalias variants of set_memory_*crypted() functions Kuppuswamy Sathyanarayanan
2022-06-24 13:19 ` Dave Hansen
2022-06-27 15:12 ` Kirill A. Shutemov
2022-06-27 18:24 ` Dave Hansen
2022-06-28 1:15 ` Kai Huang
2022-07-05 15:29 ` Kirill A. Shutemov
2022-07-18 14:22 ` Sathyanarayanan Kuppuswamy
2022-07-19 16:13 ` Kirill A. Shutemov
2022-07-19 17:10 ` Sathyanarayanan Kuppuswamy
2022-07-19 21:55 ` Kirill A. Shutemov
2022-07-20 14:56 ` Sathyanarayanan Kuppuswamy
2022-07-20 16:17 ` Kirill A. Shutemov
2022-07-20 16:58 ` Sathyanarayanan Kuppuswamy
2022-06-09 2:52 ` [PATCH v8 5/5] x86/tdx: Add Quote generation support Kuppuswamy Sathyanarayanan
2022-06-14 12:30 ` Wander Lairson Costa
2022-06-14 12:58 ` Sathyanarayanan Kuppuswamy
2022-07-21 16:08 ` Dave Hansen
2022-07-21 16:42 ` Sathyanarayanan Kuppuswamy
2022-07-21 16:49 ` Dave Hansen
2022-07-21 16:54 ` Sathyanarayanan Kuppuswamy
2022-07-21 17:02 ` Dave Hansen
2022-07-21 17:16 ` Sathyanarayanan Kuppuswamy
2022-07-21 17:19 ` Dave Hansen
2022-07-21 18:31 ` Sathyanarayanan Kuppuswamy
2022-07-21 18:42 ` Isaku Yamahata
2022-07-21 18:52 ` Dave Hansen
2022-07-21 18:57 ` Sathyanarayanan Kuppuswamy
2022-07-21 19:23 ` Dave Hansen
2022-07-21 22:08 ` Sathyanarayanan Kuppuswamy
2022-07-21 23:16 ` Kai Huang
2022-07-21 23:32 ` Kai Huang
2022-07-22 0:27 ` Dave Hansen
2022-07-22 19:05 ` Isaku Yamahata
2022-07-22 19:13 ` Dave Hansen
2022-07-22 21:18 ` Sathyanarayanan Kuppuswamy
2022-07-22 21:24 ` Dave Hansen
2022-07-25 20:19 ` Nakajima, Jun
2022-07-25 20:23 ` Dave Hansen
2022-07-25 21:56 ` Nakajima, Jun
2022-07-25 22:06 ` Sathyanarayanan Kuppuswamy
2022-08-09 6:20 ` Guorui Yu
2022-11-21 2:04 ` Guorui Yu
2022-11-21 2:26 ` Dave Hansen
2023-01-07 0:58 ` Erdem Aktas
2022-07-25 11:05 ` Kai Huang
2022-06-24 18:24 ` [PATCH v8 0/5] Add TDX Guest Attestation support Dave Hansen
2022-06-27 14:51 ` Sathyanarayanan Kuppuswamy
2022-06-27 18:51 ` Dave Hansen
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