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

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Date:   Fri, 5 Jun 2020 11:33:12 -0400
From:   Stefan Berger <stefanb@...ux.ibm.com>
To:     David Gibson <david@...son.dropbear.id.au>,
        Michael Ellerman <mpe@...erman.id.au>,
        Peter Huewe <peterhuewe@....de>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Nayna Jain <nayna@...ux.ibm.com>
Cc:     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 6/5/20 2:37 AM, 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.

Uuuh. Thanks!


> Fixes: 18b3670d79ae9 "tpm: ibmvtpm: Add support for TPM2"
> Signed-off-by: David Gibson <david@...son.dropbear.id.au>
Reviewed-by: Stefan Berger <stefanb@...ux.ibm.com>



> ---
>   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 {