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    SubjectRe: [PATCH 5/6] x86, mce: handle "action required" errors
    于 2011/12/13 5:47, Tony Luck 写道:
    > All non-urgent actions (reporting low severity errors and handling
    > "action-optional" errors) are now handled by a work queue. This
    > means that TIF_MCE_NOTIFY can be used to block execution for a
    > thread experiencing an "action-required" fault until we get all
    > cpus out of the machine check handler (and the thread that hit
    > the fault into mce_notify_process().
    >
    > We use the new mce_{save,find,clear}_info() API to get information
    > from do_machine_check() to mce_notify_process(), and then use the
    > newly improved memory_failure(..., MF_ACTION_REQUIRED) to handle
    > the error (possibly signalling the process).
    >
    > Signed-off-by: Tony Luck<tony.luck@intel.com>
    > ---
    > arch/x86/kernel/cpu/mcheck/mce.c | 64 ++++++++++++++++++++++---------------
    > 1 files changed, 38 insertions(+), 26 deletions(-)
    >
    > diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
    > index 9b83b7d..66e3bfb 100644
    > --- a/arch/x86/kernel/cpu/mcheck/mce.c
    > +++ b/arch/x86/kernel/cpu/mcheck/mce.c
    > @@ -1044,12 +1044,6 @@ void do_machine_check(struct pt_regs *regs, long error_code)
    > continue;
    > }
    >
    > - /*
    > - * Kill on action required.
    > - */
    > - if (severity == MCE_AR_SEVERITY)
    > - kill_it = 1;
    > -
    > mce_read_aux(&m, i);
    >
    > /*
    > @@ -1070,6 +1064,8 @@ void do_machine_check(struct pt_regs *regs, long error_code)
    > }
    > }
    >
    > + m = *final;
    > +
    > if (!no_way_out)
    > mce_clear_state(toclear);
    >
    > @@ -1088,7 +1084,7 @@ void do_machine_check(struct pt_regs *regs, long error_code)
    > * support MCE broadcasting or it has been disabled.
    > */
    > if (no_way_out&& tolerant< 3)
    > - mce_panic("Fatal machine check on current CPU", final, msg);
    > + mce_panic("Fatal machine check on current CPU",&m, msg);
    >
    > /*
    > * If the error seems to be unrecoverable, something should be
    > @@ -1097,11 +1093,13 @@ void do_machine_check(struct pt_regs *regs, long error_code)
    > * high, don't try to do anything at all.
    > */
    >
    > - if (kill_it&& tolerant< 3)
    > + if (worst != MCE_AR_SEVERITY&& kill_it&& tolerant< 3)
    > force_sig(SIGBUS, current);

    I think here it should add more comments to clarify why not killing *AR* case.
    Such as: "for SRAR errors, such as DCU/IFU error, on affected logical
    processors, it is reasonable that RIPV is 0."

    >
    > - /* notify userspace ASAP */
    > - set_thread_flag(TIF_MCE_NOTIFY);
    > + if (worst == MCE_AR_SEVERITY) {

    how about adding one more condition check: mce_usable_address(&m) here?

    > + mce_save_info(m.addr);
    > + set_thread_flag(TIF_MCE_NOTIFY);

    Here only SRAR error are flagged with TIF_MCE_NOTIFY, which means only SRAR
    error is handled in the function do_notify_resume. If so, SRAO error will
    only be handled in work_queue mce_work. If so, I think some related function
    names should be updated too. Otherwise, it will confuse people not touching
    these codes before.

    > + }
    >
    > if (worst> 0)
    > mce_report_event(regs);
    > @@ -1115,34 +1113,50 @@ EXPORT_SYMBOL_GPL(do_machine_check);
    > #ifndef CONFIG_MEMORY_FAILURE
    > int memory_failure(unsigned long pfn, int vector, int flags)
    > {
    > - printk(KERN_ERR "Action optional memory failure at %lx ignored\n", pfn);
    > + if (flags& MF_ACTION_REQUIRED)
    > + return -ENXIO; /* panic? */
    > + else
    > + printk(KERN_ERR "Action optional memory failure at %lx ignored\n", pfn);
    >
    > return 0;
    > }
    > #endif
    >
    > /*
    > - * Called after mce notification in process context. This code
    > - * is allowed to sleep. Call the high level VM handler to process
    > - * any corrupted pages.
    > - * Assume that the work queue code only calls this one at a time
    > - * per CPU.
    > - * Note we don't disable preemption, so this code might run on the wrong
    > - * CPU. In this case the event is picked up by the scheduled work queue.
    > - * This is merely a fast path to expedite processing in some common
    > - * cases.
    > + * Called in process context that interrupted by MCE and marked with
    > + * TIF_MCE_NOTFY, just before returning to errorneous userland.
    > + * This code is allowed to sleep.
    > + * Attempt possible recovery such as calling the high level VM handler to
    > + * process any corrupted pages, and kill/signal current process if required.
    > */
    > void mce_notify_process(void)
    > {
    > + __u64 paddr = paddr;

    you mean "__u64 paddr = 0;"?

    > unsigned long pfn;
    > - mce_notify_irq();
    > - while (mce_ring_get(&pfn))
    > - memory_failure(pfn, MCE_VECTOR, 0);
    > +
    > + if (!mce_find_info(&paddr))
    > + mce_panic("Lost address", NULL, NULL);
    > + pfn = paddr>> PAGE_SHIFT;
    > +
    > + clear_thread_flag(TIF_MCE_NOTIFY);
    > +
    > + pr_err("Uncorrected hardware memory error in user-access at %llx",
    > + paddr);
    > + if (memory_failure(pfn, MCE_VECTOR, MF_ACTION_REQUIRED)< 0) {
    > + pr_err("Memory error not recovered");
    > + force_sig(SIGBUS, current);
    > + } else {
    > + pr_err("Memory error recovered");
    > + mce_clear_info();
    > + }
    > }

    Does there exist some possibility that in the same process there are more than
    one error triggered? If so, maybe mce_find_info/mce_clear_info should be changed
    to loop-style, because here TIF_MCE_NOTIFY is cleared in the handler.

    Or it is impossible because overwritten will be covered by following condition:

    MCESEV(
    PANIC, "Action required with lost events",
    SER, BITSET(MCI_STATUS_OVER|MCI_UC_SAR)
    ),

    >
    > static void mce_process_work(struct work_struct *dummy)
    > {
    > - mce_notify_process();
    > + unsigned long pfn;
    > +
    > + while (mce_ring_get(&pfn))
    > + memory_failure(pfn, MCE_VECTOR, 0);
    > }
    >
    > #ifdef CONFIG_X86_MCE_INTEL
    > @@ -1232,8 +1246,6 @@ int mce_notify_irq(void)
    > /* Not more than two messages every minute */
    > static DEFINE_RATELIMIT_STATE(ratelimit, 60*HZ, 2);
    >
    > - clear_thread_flag(TIF_MCE_NOTIFY);
    > -
    > if (test_and_clear_bit(0,&mce_need_notify)) {
    > /* wake processes polling /dev/mcelog */
    > wake_up_interruptible(&mce_chrdev_wait);

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