Re: [PATCH 1/4] tpm_tis: Clean up locality release

[Jerry Snitselaar <jsnitsel@redhat.com>]

James Bottomley @ 2020-09-30 16:03 MST:

> On Wed, 2020-09-30 at 14:19 -0700, Jerry Snitselaar wrote:
>> James Bottomley @ 2020-09-29 15:32 MST:
>> 
>> > The current release locality code seems to be based on the
>> > misunderstanding that the TPM interrupts when a locality is
>> > released: it doesn't, only when the locality is acquired.
>> > 
>> > Furthermore, there seems to be no point in waiting for the locality
>> > to be released.  All it does is penalize the last TPM
>> > user.  However, if there's no next TPM user, this is a pointless
>> > wait and if there is
>> > a
>> > next TPM user, they'll pay the penalty waiting for the new locality
>> > (or possibly not if it's the same as the old locality).
>> > 
>> > Fix the code by making release_locality as simple write to release
>> > with no waiting for completion.
> [...]
>> My recollection is that this was added because there were some chips
>> that took so long to release locality that a subsequent
>> request_locality call was seeing the locality as already active,
>> moving on, and then the locality was getting released out from under
>> the user.
>
> Well, I could simply dump the interrupt code, which can never work and
> we could always poll.
>
> However, there also appears to be a bug in our locality requesting
> code.  We write the request and wait for the grant, but a grant should
> be signalled by not only the ACCESS_ACTIVE_LOCALITY being 1 but also
> the ACCESS_REQUEST_USE going to 0.  As you say, if we're slow to
> relinquish, ACCESS_ACTIVE_LOCALITY could already be 1 and we'd think we
> were granted, but ACCESS_REQUEST_USE should stay 1 until the TPM
> actually grants the next request.
>
> If I code up a fix is there any chance you still have access to a
> problem TPM?  Mine all seem to grant and release localities fairly
> instantaneously.
>
> James

Sorry, I seemed to make a mess of it. I don't have access to a system where it
occurred, but cc'ing Laurent since he reported the problem and might
still have access to the system.

I'd say fix up the check for locality request to look at
ACCESS_REQUEST_USE, and go with this patch to clean up locality release.
Hopefully Laurent still has access and can test. I do have a laptop now
where I should be able to test the other bits in your patchset since
this is one of the models that hit interrupt storm problem when Stefan's
2 patches were originally applied. Lenovo applied a fix to their bios,
but this should still have the older one version that has the issue. I'm
on PTO this week, but I will try to spend some time in the next couple
days reproducing and then trying your patches.

Regards,
Jerry