linux-kernel - Re: [PATCHv2] tpm: ibmvtpm: Wait for ready buffer before probing for TPM2 attributes

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Date:   Thu, 18 Jun 2020 20:42:40 -0700
From:   Jerry Snitselaar <jsnitsel@...hat.com>
To:     David Gibson <david@...son.dropbear.id.au>
Cc:     jarkko.sakkinen@...ux.intel.com, stefanb@...ux.ibm.com,
        mpe@...erman.id.au, peterhuewe@....de, jgg@...pe.ca,
        nayna@...ux.ibm.com, paulus@...ba.org,
        linuxppc-dev@...ts.ozlabs.org, linux-integrity@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2] tpm: ibmvtpm: Wait for ready buffer before probing for
 TPM2 attributes

On Fri Jun 19 20, 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.
>
>To fix it, just move the tpm2_get_cc_attrs_tlb() call after the
>existing code to wait for initialization, which will ensure the buffer
>is allocated.
>
>Fixes: 18b3670d79ae9 ("tpm: ibmvtpm: Add support for TPM2")
>Signed-off-by: David Gibson <david@...son.dropbear.id.au>
>---

Reviewed-by: Jerry Snitselaar <jsnitsel@...hat.com>

>
>Changes from v1:
> * Fixed a formatting error in the commit message
> * Added some more detail to the commit message
>
>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 09fe45246b8cc..994385bf37c0c 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
>