linux-kernel - Re: [PATCH] tpm_crb: Add idle support for the Arm FF-A start method

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Message-ID: <91d8e71a-7013-43d7-9d04-9a191fed50e9@arm.com>
Date: Wed, 15 Oct 2025 17:22:53 -0500
From: Stuart Yoder <stuart.yoder@....com>
To: Jarkko Sakkinen <jarkko@...nel.org>
Cc: linux-integrity@...r.kernel.org, peterhuewe@....de, jgg@...pe.ca,
 sudeep.holla@....com, Prachotan.Bathi@....com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tpm_crb: Add idle support for the Arm FF-A start method



On 8/25/25 5:49 PM, Jarkko Sakkinen wrote:
> On Mon, Aug 25, 2025 at 05:19:34PM -0500, Stuart Yoder wrote:
>>
>>
>> On 8/25/25 4:58 PM, Jarkko Sakkinen wrote:
>>> On Mon, Aug 25, 2025 at 03:59:43PM -0500, Stuart Yoder wrote:
>>>> According to the CRB over FF-A specification [1], a TPM that implements
>>>> the ABI must comply with the TCG PTP specification. This requires support
>>>> for the Idle and Ready states.
>>>>
>>>> This patch implements CRB control area requests for goIdle and
>>>> cmdReady on FF-A based TPMs.
>>>>
>>>> The FF-A message used to notify the TPM of CRB updates includes a
>>>> locality parameter, which provides a hint to the TPM about which
>>>> locality modified the CRB.  This patch adds a locality parameter
>>>> to __crb_go_idle() and __crb_cmd_ready() to support this.
>>>>
>>>> [1] https://developer.arm.com/documentation/den0138/latest/
>>>>
>>>> Signed-off-by: Stuart Yoder <stuart.yoder@....com>
>>>
>>> Perhaps a dummy question but is this "QEMU testable"? I know how
>>> to bind swtpm to QEMU and make it appear as CRB device on x86-64.
>>>
>>> I don't see much testing happening with these ARM CRB patches,
>>> and if that works in the first palce  I could probably add
>>> a new board target to my BR2_EXTERNAL [1].
>>>
>>> I can of course do "negative testing' i.e. that these don't
>>> break x86 ;-)
>>
>> Unfortunately this is not currently testable on QEMU.  We are using
>> the Arm FVP [1], which is also a machine emulator, with the firmware
>> stack and an fTPM running in TrustZone.  The firmware, fTPM, etc are
>> not all publicly available yet, but everything is based on open
>> source projects and the intent is that all the components needed do
>> test this on FVP will be available at some point.
>>
>> There is nothing fundamental that would prevent this from running
>> on QEMU, but just a fair amount of integration and possibly firmware
>> work.
> 
> OK, it's cool and the patch looks totally fine and I can
> "hallucinate it" so:
> 
> Reviewed-by: Jarkko Sakkinen <jarkko@...nel.org>

Hi Jarkko,

It looks like this patch did not make it into 6.18.  I wanted to make
sure it didn't get lost.  Will it be queued up for 6.19?

Thanks,
Stuart