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

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Message-ID: <aPN59bwcUrieMACf@kernel.org>
Date: Sat, 18 Oct 2025 14:28:53 +0300
From: Jarkko Sakkinen <jarkko@...nel.org>
To: Stuart Yoder <stuart.yoder@....com>
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 Wed, Oct 15, 2025 at 05:22:53PM -0500, Stuart Yoder wrote:
> 
> 
> 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?

Totally my fault, sorry. There was a bit shuffling with TCG_TPM2_HMAC and
some other things, and this one slipped over :-/

Since it is non-intrusive despite not a bug fix,  I think I can put out
-rc2 pull request to Linus, and see if he sees this acceptable.

> 
> Thanks,
> Stuart

BR, Jarkko