x86/mce: Handle "action required" errors

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>

1 files changed, 53 insertions, 42 deletions

diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index e1579c5a71da..56e4e79387c3 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 +1058,9 @@ void do_machine_check(struct pt_regs *regs, long error_code)
                 }
         }
 
+        /* mce_clear_state will clear *final, save locally for use later */
+        m = *final;
+
         if (!no_way_out)
                 mce_clear_state(toclear);
 
@@ -1073,27 +1072,22 @@ void do_machine_check(struct pt_regs *regs, long error_code)
                 no_way_out = worst >= MCE_PANIC_SEVERITY;
 
         /*
-         * If we have decided that we just CAN'T continue, and the user
-         * has not set tolerant to an insane level, give up and die.
-         *
-         * This is mainly used in the case when the system doesn't
-         * support MCE broadcasting or it has been disabled.
+         * At insane "tolerant" levels we take no action. Otherwise
+         * we only die if we have no other choice. For less serious
+         * issues we try to recover, or limit damage to the current
+         * process.
          */
-        if (no_way_out && tolerant < 3)
-                mce_panic("Fatal machine check on current CPU", final, msg);
-
-        /*
-         * If the error seems to be unrecoverable, something should be
-         * done.  Try to kill as little as possible.  If we can kill just
-         * one task, do that.  If the user has set the tolerance very
-         * high, don't try to do anything at all.
-         */
-
-        if (kill_it && tolerant < 3)
-                force_sig(SIGBUS, current);
-
-        /* notify userspace ASAP */
-        set_thread_flag(TIF_MCE_NOTIFY);
+        if (tolerant < 3) {
+                if (no_way_out)
+                        mce_panic("Fatal machine check on current CPU", &m, msg);
+                if (worst == MCE_AR_SEVERITY) {
+                        /* schedule action before return to userland */
+                        mce_save_info(m.addr);
+                        set_thread_flag(TIF_MCE_NOTIFY);
+                } else if (kill_it) {
+                        force_sig(SIGBUS, current);
+                }
+        }
 
         if (worst > 0)
                 mce_report_event(regs);
@@ -1107,6 +1101,8 @@ EXPORT_SYMBOL_GPL(do_machine_check);
 #ifndef CONFIG_MEMORY_FAILURE
 int memory_failure(unsigned long pfn, int vector, int flags)
 {
+        /* mce_severity() should not hand us an ACTION_REQUIRED error */
+        BUG_ON(flags & MF_ACTION_REQUIRED);
         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 +1111,44 @@ 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_NOTIFY, just before returning to erroneous 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 physical address for unconsumed uncorrectable error", 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);
+        }
+        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 +1238,6 @@ 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);