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Date: Wed, 14 Dec 2011 17:28:26 +0800
From: Chen Gong <gong.chen@...ux.intel.com>
To: Tony Luck <tony.luck@...el.com>
CC: linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
Borislav Petkov <bp@...64.org>,
"Huang, Ying" <ying.huang@...el.com>,
Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
Subject: Re: [PATCH 5/6] x86, mce: handle "action required" errors
δΊ 2011/12/13 5:47, Tony Luck ει:
> 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@...el.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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