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

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Date:   Tue, 23 Jun 2020 03:48:13 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     David Gibson <david@...son.dropbear.id.au>
Cc:     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, 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@...son.dropbear.id.au>

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

/Jarkko