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>>>>>> + struct rdt_resource *r; >>>>>> + u32 evt_cfg = 0; >>>>>> + int ret = 0; >>>>>> + >>>>>> + /* Valid input requires a trailing newline */ >>>>>> + if (nbytes == 0 || buf[nbytes - 1] != '\n') >>>>>> + return -EINVAL; >>>>>> + >>>>>> + buf[nbytes - 1] = '\0'; >>>>>> + >>>>>> + cpus_read_lock(); >>>>>> + mutex_lock(&rdtgroup_mutex); >>>>>> + >>>>>> + rdt_last_cmd_clear(); >>>>>> + >>>>>> + r = resctrl_arch_get_resource(mevt->rid); >>>>>> + if (!resctrl_arch_mbm_cntr_assign_enabled(r)) { >>>>>> + rdt_last_cmd_puts("mbm_event counter assignment mode is not enabled\n"); >>>>>> + ret = -EINVAL; >>>>>> + goto out_unlock; >>>>>> + } >>>>>> + >>>>>> + ret = resctrl_parse_mem_transactions(buf, &evt_cfg); >>>>>> + if (!ret && mevt->evt_cfg != evt_cfg) { >>>>> ... is evt_cfg of 0 (a) a valid value (that will not cause hardware to fault) and >>>>> (b) a reasonable value to allow? >>>>> >>>> The value evt_cfg = 0 is valid and permitted for both ABMC and BMEC. I >>>> have confirmed here through verification and testing. In that case, the >>>> event counter will not be monitoring anything. >>> Thank you for checking. >>> >>> I do not know what a use case for this would be but I also do not see why kernel >>> should prevent user space from doing this. Looks like event_filter_show() will then >>> just print a '\n' that is expected. Are counters expected to always return 0 in this >>> case or will they return an error? I am not clear on what qualifies as "invalid counter >>> configuration" for ABMC that results in RMID_VAL_ERROR. >> The event counters return 0 in this case. I would not think this as an >> invalid event configuration. >> >> One option is to add a text in last_cmd_status from event_filter_show(). >> >> rdt_last_cmd_printf("Event %s is not configured to monitor any memory >> transactions\n", mevt->name); > > event_filter_show() does not return an error in this case so a user may not > check last_cmd_status since the doc specifies that "If the command was successful, > it will read as "ok"." Since the write() succeeded we should not fail the associated > show() to prompt the user to check last_cmd_status though. > > Even so, an additional message does not seem necessary to me because as I understand > event_filter_show() returns an empty (just a '\n') file that I think > already reflects that no memory transactions are configured. It remains an awkward > use case to me but from what you stated this is valid for the hardware, it is what the > user requested, and the user can use interface to confirm the state. It does not seem > like changes are needed for this scenario. Sure.  Sounds good. Thanks Babu