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

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Message-ID: <pxtojuqebtk7pa5vjbhmiulydmgyutsbgxg2j5b6ziyxzqls35@qmmmcn4uwzie>
Date: Tue, 6 May 2025 15:06:22 +0200
From: Stefano Garzarella <sgarzare@...hat.com>
To: Jarkko Sakkinen <jarkko@...nel.org>
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 Wed, Apr 30, 2025 at 06:49:37PM +0300, Jarkko Sakkinen wrote:
>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.

I see, I'll replace the "So we can set..." paragraph with your 
suggestion on the previous patch.

Thanks,
Stefano

>
>> ---
>>  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
>