Re: [RFC 0/4] tpm_crb: Add command and response buffer chunking support

[Stefan Berger <stefanb@linux.ibm.com>]

On 4/23/26 6:43 AM, Arun Menon wrote:
> On Wed, Apr 08, 2026 at 11:34:54AM +0300, Jarkko Sakkinen wrote:
>> On Tue, Mar 24, 2026 at 06:11:11PM +0530, Arun Menon wrote:
>>> Hi Jarkko,
>>>
>>> On Tue, Mar 24, 2026 at 12:41:26PM +0200, Jarkko Sakkinen wrote:
>>>> On Tue, Mar 24, 2026 at 12:47:59PM +0530, Arun Menon wrote:
>>>>> The new version of TCG TPM v185 (currently under review [1]) supports
>>>>> sending data/commands in chunks for the CRB (Command Response Buffer)
>>>>> interface. This is in line with the initiative to support PQC algorithms.
>>>>>
>>>>> This series implements the logic to send and receive larger TPM
>>>>> cmd/rsp between the linux guest and the TPM backend in chunks.
>>>>> Currently, the TPM CRB driver is limited by the physical size of the
>>>>> MMIO window. When userspace attempts to send a payload that exceeds this
>>>>> size, the driver rejects it.
>>>>>
>>>>> This series introduces chunking support. The driver now checks the CRB
>>>>> interface capability for CRB_INTF_CAP_CRB_CHUNK. If supported by the
>>>>> backend, the driver will slice oversized commands into MMIO-sized
>>>>> chunks, signalling the backend via CRB_START_NEXT_CHUNK, and finalizing
>>>>> with CRB_START_INVOKE. Responses are also read back in a similar chunked
>>>>> manner.
>>>>>
>>>>> If the backend does not support chunking, the driver retains its legacy
>>>>> behaviour and enforces the standard size limits.
>>>>>
>>>>> This feature also requires the QEMU to interpret the data in chunks and
>>>>> forward it to the TPM backend and subsequently dispatch the TPM response
>>>>> in chunks back to the linux guest. This is implemented in [2]
>>>>>
>>>>> [1] https://trustedcomputinggroup.org/wp-content/uploads/PC-Client-Specific-Platform-TPM-Profile-for-TPM-2p0-v1p07_rc1_121225.pdf
>>>>> [2] https://lore.kernel.org/qemu-devel/20260319135316.37412-1-armenon@redhat.com/
>>>>>
>>>>> Arun Menon (4):
>>>>>    tpm_crb: Add definition of TPM CRB chunking fields
>>>>>    tpm_crb: Add new wrapper function to invoke start method
>>>>>    tpm_crb: Implement command and response chunking logic
>>>>>    tpm: Increase TPM_BUFSIZE to 64kB for chunking support

64kb? I am only increasing the TPM buffer to 8kb. More does not seem to 
be necessary.

>>>>>
>>>>>   drivers/char/tpm/tpm.h     |   2 +-
>>>>>   drivers/char/tpm/tpm_crb.c | 194 ++++++++++++++++++++++++++-----------
>>>>>   2 files changed, 137 insertions(+), 59 deletions(-)
>>>>>
>>>>> -- 
>>>>> 2.53.0
>>>>>
>>>>
>>>> When QEMU has the feature available?
>>>
>>> The QEMU patches are in review at the moment,
>>> here is the link: https://lore.kernel.org/qemu-devel/20260319135316.37412-1-armenon@redhat.com/
>>> Hoping to have them merged soon.
>>
>> Right, and additional question: what about swtpm?

I am waiting for https://github.com/trustedComputingGroup/tpm to show 
rev185 with PQC support so that I can merge my patches based on 'their' 
PQC support into the public libtpms repo.