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    SubjectRe: [PATCH v7 07/10] tmp, tmp_tis: Implement usage counter for locality
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    On 04.07.22 19:45, Lino Sanfilippo wrote:
    >
    >
    > On 01.07.22 01:29, Jarkko Sakkinen wrote:
    >
    >>
    >> I'm kind of thinking that should tpm_tis_data have a lock for its
    >> contents?
    >
    > Most of the tpm_tis_data structure elements are set once during init and
    > then never changed but only read. So no need for locking for these. The
    > exceptions I see are
    >
    > - flags
    > - locality_count
    > - locality
    >
    >
    > whereby "flags" is accessed by atomic bit manipulating functions and thus
    > does not need extra locking. "locality_count" is protected by the locality_count_mutex.
    > "locality" is only set in check_locality() which is called from tpm_tis_request_locality_locked()
    > which holds the locality_count_mutex. So check_locality() is also protected by the locality_count_mutex
    > (which for this reason should probably rather be called locality_mutex since it protects both the "locality_count"
    > and the "locality" variable).
    >
    > There is one other place check_locality() is called from, namely the interrupt handler. This is also the only
    > place in which "locality" could be assigned another value than 0 (aka the default). In this case there
    > is no lock, so this could indeed by racy.
    >
    > The solution I see for this is:
    > 1. remove the entire loop that checks for the current locality, i.e. this code:
    >
    > if (interrupt & TPM_INTF_LOCALITY_CHANGE_INT)
    > for (i = 0; i < 5; i++)
    > if (check_locality(chip, i))
    > break;
    >
    > So we avoid "locality" from being changed to something that is not the default.
    >
    >

    I wonder if we need tpm_tis_data->locality at all: the claimed locality is already tracked in
    chip->locality and in TPM TIS we never use anything else than locality 0 so it never changes.

    Is there any good reason not to remove it?



    Regards,
    Lino

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