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Subject[PATCH 5/6] x86, mce: handle "action required" errors (unjumbled version)
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).
Update some comments to make the new code flows clearer.

Signed-off-by: Tony Luck <tony.luck@intel.com>
---
[Version posted earlier had the diff included in the commit comment,
and then the real copy of the diff - making it hard to read. Sorry.]

arch/x86/kernel/cpu/mcheck/mce.c | 71 ++++++++++++++++++++++++--------------
1 files changed, 45 insertions(+), 26 deletions(-)
diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index 7d7303a..dfd20a6 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -982,7 +982,9 @@ void do_machine_check(struct pt_regs *regs, long error_code)
barrier();

/*
- * When no restart IP must always kill or panic.
+ * When no restart IP might need to kill or panic.
+ * Assume the worst for now, but if we find the
+ * severity is MCE_AR_SEVERITY we have other options.
*/
if (!(m.mcgstatus & MCG_STATUS_RIPV))
kill_it = 1;
@@ -1036,12 +1038,6 @@ 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);

/*
@@ -1062,6 +1058,8 @@ void do_machine_check(struct pt_regs *regs, long error_code)
}
}

+ m = *final;
+
if (!no_way_out)
mce_clear_state(toclear);

@@ -1080,7 +1078,7 @@ 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
@@ -1089,11 +1087,13 @@ 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);

- /* notify userspace ASAP */
- set_thread_flag(TIF_MCE_NOTIFY);
+ if (worst == MCE_AR_SEVERITY) {
+ mce_save_info(m.addr);
+ set_thread_flag(TIF_MCE_NOTIFY);
+ }

if (worst > 0)
mce_report_event(regs);
@@ -1107,6 +1107,8 @@ EXPORT_SYMBOL_GPL(do_machine_check);
#ifndef CONFIG_MEMORY_FAILURE
int memory_failure(unsigned long pfn, int vector, int flags)
{
+ if (flags & MF_ACTION_REQUIRED)
+ return -ENXIO; /* panic? */
printk(KERN_ERR "Uncorrected memory error in page 0x%lx ignored\n"
"Rebuild kernel with CONFIG_MEMORY_FAILURE=y for smarter handling\n", pfn);

@@ -1115,27 +1117,46 @@ int memory_failure(unsigned long pfn, int vector, int flags)
#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.
+ * Action required errors are handled here.
*/
void mce_notify_process(void)
{
unsigned long pfn;
- mce_notify_irq();
- while (mce_ring_get(&pfn))
- memory_failure(pfn, MCE_VECTOR, 0);
+ struct mce_info *mi = mce_find_info();
+
+ if (!mi)
+ mce_panic("Lost address", NULL, NULL);
+ pfn = mi->paddr >> PAGE_SHIFT;
+
+ clear_thread_flag(TIF_MCE_NOTIFY);
+
+ pr_err("Uncorrected hardware memory error in user-access at %llx",
+ mi->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(mi);
}

+/*
+ * Action optional processing happens here (picking up
+ * from the list of faulting pages that do_machine_check()
+ * placed into the "ring").
+ */
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
@@ -1225,8 +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);
--
1.7.3.1


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