[PATCHv2] tpm: ibmvtpm: Wait for ready buffer before probing for TPM2 attributes

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@gibson.dropbear.id.au>
---

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(-)

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@gibson.dropbear.id.au>
>---

Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.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
>

On Fri, Jun 19, 2020 at 01:30:40PM +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.
> 
> 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@gibson.dropbear.id.au>

Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>

/Jarkko