linux-kernel - Re: [PATCH v3 4/4] tpm/tpm_svsm: support TPM_CHIP_FLAG

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Message-ID: <aBJGkSil1YAzSXsg@kernel.org>
Date: Wed, 30 Apr 2025 18:49:37 +0300
From: Jarkko Sakkinen <jarkko@...nel.org>
To: Stefano Garzarella <sgarzare@...hat.com>
Cc: Christophe Leroy <christophe.leroy@...roup.eu>,
	Peter Huewe <peterhuewe@....de>,
	Alexandre Belloni <alexandre.belloni@...tlin.com>,
	Jens Wiklander <jens.wiklander@...aro.org>,
	Claudiu Beznea <claudiu.beznea@...on.dev>,
	Naveen N Rao <naveen@...nel.org>,
	Nicholas Piggin <npiggin@...il.com>, linuxppc-dev@...ts.ozlabs.org,
	Nicolas Ferre <nicolas.ferre@...rochip.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	linux-integrity@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Sumit Garg <sumit.garg@...nel.org>, linux-kernel@...r.kernel.org,
	Jason Gunthorpe <jgg@...pe.ca>
Subject: Re: [PATCH v3 4/4] tpm/tpm_svsm: support TPM_CHIP_FLAG_SYNC

On Mon, Apr 14, 2025 at 04:56:53PM +0200, Stefano Garzarella wrote:
> From: Stefano Garzarella <sgarzare@...hat.com>
> 
> This driver does not support interrupts, and receiving the response is
> synchronous with sending the command.
> 
> So we can set TPM_CHIP_FLAG_SYNC to support synchronous send() and
> return responses in the same buffer used for commands. This way we
> don't need to implement recv() op.
> 
> Keep using the same pre-allocated buffer to avoid having to allocate
> it for each command. We need the buffer to have the header required by
> the SVSM protocol and the command contiguous in memory.
> 
> Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>

Similar comments, and a bit redundancy does not matter i.e., they can
have pretty much the same explanation.

> ---
>  drivers/char/tpm/tpm_svsm.c | 27 +++++++++++----------------
>  1 file changed, 11 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm_svsm.c b/drivers/char/tpm/tpm_svsm.c
> index d3ca5615b6f7..db1983072345 100644
> --- a/drivers/char/tpm/tpm_svsm.c
> +++ b/drivers/char/tpm/tpm_svsm.c
> @@ -25,38 +25,32 @@ struct tpm_svsm_priv {
>  	void *buffer;
>  };
>  
> -static int tpm_svsm_send(struct tpm_chip *chip, u8 *buf, size_t len,
> +static int tpm_svsm_send(struct tpm_chip *chip, u8 *buf, size_t cmd_len,
>  			 size_t buf_size)
>  {
>  	struct tpm_svsm_priv *priv = dev_get_drvdata(&chip->dev);
>  	int ret;
>  
> -	ret = svsm_vtpm_cmd_request_fill(priv->buffer, 0, buf, len);
> +	ret = svsm_vtpm_cmd_request_fill(priv->buffer, 0, buf, cmd_len);
>  	if (ret)
>  		return ret;
>  
>  	/*
>  	 * The SVSM call uses the same buffer for the command and for the
> -	 * response, so after this call, the buffer will contain the response
> -	 * that can be used by .recv() op.
> +	 * response, so after this call, the buffer will contain the response.
> +	 *
> +	 * Note: we have to use an internal buffer because the device in SVSM
> +	 * expects the svsm_vtpm header + data to be physically contiguous.
>  	 */
> -	return snp_svsm_vtpm_send_command(priv->buffer);
> -}
> -
> -static int tpm_svsm_recv(struct tpm_chip *chip, u8 *buf, size_t len)
> -{
> -	struct tpm_svsm_priv *priv = dev_get_drvdata(&chip->dev);
> +	ret = snp_svsm_vtpm_send_command(priv->buffer);
> +	if (ret)
> +		return ret;
>  
> -	/*
> -	 * The internal buffer contains the response after we send the command
> -	 * to SVSM.
> -	 */
> -	return svsm_vtpm_cmd_response_parse(priv->buffer, buf, len);
> +	return svsm_vtpm_cmd_response_parse(priv->buffer, buf, buf_size);
>  }
>  
>  static struct tpm_class_ops tpm_chip_ops = {
>  	.flags = TPM_OPS_AUTO_STARTUP,
> -	.recv = tpm_svsm_recv,
>  	.send = tpm_svsm_send,
>  };
>  
> @@ -85,6 +79,7 @@ static int __init tpm_svsm_probe(struct platform_device *pdev)
>  
>  	dev_set_drvdata(&chip->dev, priv);
>  
> +	chip->flags |= TPM_CHIP_FLAG_SYNC;
>  	err = tpm2_probe(chip);
>  	if (err)
>  		return err;
> -- 
> 2.49.0
> 

BR, Jarkko