Hi Xie XiuQi, On 05/12/2018 02:02, Xie XiuQi wrote: > On 2018/12/4 2:06, James Morse wrote: >> memory_failure() offlines or repairs pages of memory that have been >> discovered to be corrupt. These may be detected by an external >> component, (e.g. the memory controller), and notified via an IRQ. >> In this case the work is queued as not all of memory_failure()s work >> can happen in IRQ context. >> >> If the error was detected as a result of user-space accessing a >> corrupt memory location the CPU may take an abort instead. On arm64 >> this is a 'synchronous external abort', and on a firmware first >> system it is replayed using NOTIFY_SEA. >> >> This notification has NMI like properties, (it can interrupt >> IRQ-masked code), so the memory_failure() work is queued. If we >> return to user-space before the queued memory_failure() work is >> processed, we will take the fault again. This loop may cause platform >> firmware to exceed some threshold and reboot when Linux could have >> recovered from this error. >> >> If a ghes notification type indicates that it may be triggered again >> when we return to user-space, use the task-work and notify-resume >> hooks to kick the relevant memory_failure() queue before returning >> @@ -407,7 +447,22 @@ static void ghes_handle_memory_failure(struct acpi_hest_generic_data *gdata, int >> >> if (flags != -1) >> memory_failure_queue(pfn, flags); > > We may need to take MF_ACTION_REQUIRED flags for memory_failure() in SEA condition. Hmmm, I'd forgotten about the extra flags. They're only used by x86's do_machine_check(), which knows more about what is going on. I agree we do know it should be a 'MF_ACTION_REQUIRED' for Synchronous-external-abort, but I'd really like all the notifications to behave in the same way as we can't change which notification firmware uses. (This ghes_is_synchronous() affects when memory_failure() runs, not what it does.) What happens if we miss MF_ACTION_REQUIRED? Surely the page still gets unmapped as its PG_Poisoned, an AO signal may be pending, but if user-space touches the page it will get an AR signal. Is this just about removing an extra AO signal to user-space? If we do need this, I'd like to pick it up from the CPER records, as x86's NOTIFY_NMI looks like it covers both AO/AR cases. (as does NOTIFY_SDEI). The Master/Target abort or Invalid-address types in the memory-error-section CPER records look like the best bet. > And there is no return value check for memory_failure() in memory_failure_work_func(), > I'm not sure whether we need to check the return value. What would we do if it fails? The reasons look fairly broad, -EBUSY can mean "(page) still referenced by [..] users", 'thp split failed' or 'page already poisoned'. I don't think the behaviour or return-codes are consistent enough to use. > If the recovery fails here, we need to take other actions, such as force to send a SIGBUS signal. We don't do this today. If it fixes some mis-behaviour, and we can key it from something in the CPER records then I'm all ears! Thanks, James
