linux-kernel - Re: [PATCH] tpm: ibmvtpm: Wait for ready buffer before probing for TPM2 attributes

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Date:   Wed, 17 Jun 2020 00:08:08 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     David Gibson <david@...son.dropbear.id.au>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Peter Huewe <peterhuewe@....de>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Stefan Berger <stefanb@...ux.ibm.com>,
        Nayna Jain <nayna@...ux.ibm.com>,
        Paul Mackerras <paulus@...ba.org>,
        linuxppc-dev@...ts.ozlabs.org, linux-integrity@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tpm: ibmvtpm: Wait for ready buffer before probing for
 TPM2 attributes

On Fri, Jun 05, 2020 at 04:37:19PM +1000, David Gibson wrote:
> The tpm2_get_cc_attrs_tbl() call will result in TPM commands being issued,
> which will need the use of the internal command/response buffer.  But,
> we're issuing this *before* we've waited to make sure that buffer is
> allocated.
> 
> This can result in intermittent failures to probe if the hypervisor / TPM
> implementation doesn't respond quickly enough.  I find it fails almost
> every time with an 8 vcpu guest under KVM with software emulated TPM.
> 
> Fixes: 18b3670d79ae9 "tpm: ibmvtpm: Add support for TPM2"

Should be Fixes: 18b3670d79ae ("tpm: ibmvtpm: Add support for TPM2")

Also briefly state what the commit does, not just the problem
description. The code change looks legit.

Please send v2 with these changes.

> Signed-off-by: David Gibson <david@...son.dropbear.id.au>
> ---
>  drivers/char/tpm/tpm_ibmvtpm.c | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm_ibmvtpm.c b/drivers/char/tpm/tpm_ibmvtpm.c
> index 09fe45246b8c..994385bf37c0 100644
> --- a/drivers/char/tpm/tpm_ibmvtpm.c
> +++ b/drivers/char/tpm/tpm_ibmvtpm.c
> @@ -683,13 +683,6 @@ static int tpm_ibmvtpm_probe(struct vio_dev *vio_dev,
>  	if (rc)
>  		goto init_irq_cleanup;
>  
> -	if (!strcmp(id->compat, "IBM,vtpm20")) {
> -		chip->flags |= TPM_CHIP_FLAG_TPM2;
> -		rc = tpm2_get_cc_attrs_tbl(chip);
> -		if (rc)
> -			goto init_irq_cleanup;
> -	}
> -
>  	if (!wait_event_timeout(ibmvtpm->crq_queue.wq,
>  				ibmvtpm->rtce_buf != NULL,
>  				HZ)) {
> @@ -697,6 +690,13 @@ static int tpm_ibmvtpm_probe(struct vio_dev *vio_dev,
>  		goto init_irq_cleanup;
>  	}
>  
> +	if (!strcmp(id->compat, "IBM,vtpm20")) {
> +		chip->flags |= TPM_CHIP_FLAG_TPM2;
> +		rc = tpm2_get_cc_attrs_tbl(chip);
> +		if (rc)
> +			goto init_irq_cleanup;
> +	}
> +
>  	return tpm_chip_register(chip);
>  init_irq_cleanup:
>  	do {
> -- 
> 2.26.2
> 

/Jarkko