On Sat, Sep 16, 2017 at 08:36:29AM -0700, Jarkko Sakkinen wrote:
> Hi
>
> While sitting at the airport I started to think a bit about the context
> gap issue.
>
> I think first thing that would make sense would be to have a 64-bit
> shadow count for every TPM space i.e.
>
> atomic_long_t tpm2_ctx_cnt;
>
> struct tpm2_space {
> /* ... */
> u64 ctx_cnt;
> };
>
> For every create and load of a session you will read the global count
> and increase it. This way we have get a well defined order.
>
> With this organization we could for example put tpm spaces to a
> red-black tree and refresh the oldest tpm space (just first thought
> that came to mind).
>
> PS. While doing LPC and LSS slides I found error from the TPM 2.0
> commands specification. TPM2_ContextSave can never emit
> TPM2_RC_CONTEXT_GAP albeit the specification says so.
>
> /Jarkko
Other than context gap it would probably make sense to estimate TPM
capacity in order to make implementation more intelligent. We could
measure memory capacity of a TPM in the driver initialization by filling
it with fixed size dummy objects.
TPM2_GetCapability gives stuff that cannot be really trusted as spec
compliant TPM HW could just return always '1' for max.
/Jarkko
