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

[Jarkko Sakkinen]

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@xxxxxxxxxx/
> 
> 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
> 
>  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?

BR, Jarkko