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

[Stefan Berger]

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@xxxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>



> ---
>   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 {