[PATCH 0/6] x86, mce: machine check recovery for applications

[PATCH 0/6] x86, mce: machine check recovery for applications

[Tony Luck]

This series adds code to recognise the machine check signature for
a recoverable error in the data path (Advanced SKUs of "Sandy Bridge"
server processors are the first to be able to allow s/w recovery for
this case), save the required information in the machine check handler
and then call to the generic memory_failure() code to try for
graceful error recovery (sending SIGBUS to affected process(es)).

Updates since last version (December 15th)

Part1-4: unchanged

Part5: Changed stub function for CONFIG_MEMORY_FAILURE=n case to BUG_ON
if it is handed an MF_ACTION_REQUIRED case (this indicates an error in
severity calculation). Drop "Memory error recovered" message (enough
chatter already).

Part6: Only pass back an ACTION_REQUIRED severity to a kernel if it is built
with CONFIG_MEMORY_FAILURE=y (i.e. has the code to take the action).

Whole series is available in:

	git://git.kernel.org/pub/scm/linux/kernel/git/ras/ras.git mce-recovery

Tony Luck (6):
  HWPOISON: clean up memory_failure() vs. __memory_failure()
  HWPOISON: Add code to handle "action required" errors.
  x86, mce: create helper function to save addr/misc when needed
  x86, mce: Add mechanism to safely save information in MCE handler
  x86, mce: handle "action required" errors
  x86, mce: Recognise machine check bank signature for data path error

 arch/x86/kernel/cpu/mcheck/mce-severity.c |   16 +++-
 arch/x86/kernel/cpu/mcheck/mce.c          |  179 ++++++++++++++++++++---------
 drivers/base/memory.c                     |    2 +-
 include/linux/mm.h                        |    4 +-
 mm/hwpoison-inject.c                      |    4 +-
 mm/madvise.c                              |    2 +-
 mm/memory-failure.c                       |   96 ++++++++--------
 7 files changed, 197 insertions(+), 106 deletions(-)

-- 
1.7.3.1

[PATCH 2/6] HWPOISON: Add code to handle "action required" errors.

[Tony Luck]

Add new flag bit "MF_ACTION_REQUIRED" to be used by machine check
code to force a signal with si_code = BUS_MCEERR_AR in the case
where the error occurs in processor execution context. Pass the
flags argument along call chain:
	memory_failure()
	  hwpoison_user_mappings()
	    kill_procs()
	      kill_proc()

Drop the "_ao" suffix from kill_procs_ao() and kill_proc_ao() since
they can now handle "action required" as well as "action optional" errors.

Acked-by: Borislav Petkov <bp@amd64.org>
Signed-off-by: Tony Luck <tony.luck@intel.com>
---
 include/linux/mm.h  |    1 +
 mm/memory-failure.c |   50 +++++++++++++++++++++++++++++---------------------
 2 files changed, 30 insertions(+), 21 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index bcc5234..bf169ca 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1606,6 +1606,7 @@ void vmemmap_populate_print_last(void);
 
 enum mf_flags {
 	MF_COUNT_INCREASED = 1 << 0,
+	MF_ACTION_REQUIRED = 1 << 1,
 };
 extern int memory_failure(unsigned long pfn, int trapno, int flags);
 extern void memory_failure_queue(unsigned long pfn, int trapno, int flags);
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index ab259bb..95fd307 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -187,33 +187,40 @@ int hwpoison_filter(struct page *p)
 EXPORT_SYMBOL_GPL(hwpoison_filter);
 
 /*
- * Send all the processes who have the page mapped an ``action optional''
- * signal.
+ * Send all the processes who have the page mapped a signal.
+ * ``action optional'' if they are not immediately affected by the error
+ * ``action required'' if error happened in current execution context
  */
-static int kill_proc_ao(struct task_struct *t, unsigned long addr, int trapno,
-			unsigned long pfn, struct page *page)
+static int kill_proc(struct task_struct *t, unsigned long addr, int trapno,
+			unsigned long pfn, struct page *page, int flags)
 {
 	struct siginfo si;
 	int ret;
 
 	printk(KERN_ERR
-		"MCE %#lx: Killing %s:%d early due to hardware memory corruption\n",
+		"MCE %#lx: Killing %s:%d due to hardware memory corruption\n",
 		pfn, t->comm, t->pid);
 	si.si_signo = SIGBUS;
 	si.si_errno = 0;
-	si.si_code = BUS_MCEERR_AO;
 	si.si_addr = (void *)addr;
 #ifdef __ARCH_SI_TRAPNO
 	si.si_trapno = trapno;
 #endif
 	si.si_addr_lsb = compound_trans_order(compound_head(page)) + PAGE_SHIFT;
-	/*
-	 * Don't use force here, it's convenient if the signal
-	 * can be temporarily blocked.
-	 * This could cause a loop when the user sets SIGBUS
-	 * to SIG_IGN, but hopefully no one will do that?
-	 */
-	ret = send_sig_info(SIGBUS, &si, t);  /* synchronous? */
+
+	if ((flags & MF_ACTION_REQUIRED) && t == current) {
+		si.si_code = BUS_MCEERR_AR;
+		ret = force_sig_info(SIGBUS, &si, t);
+	} else {
+		/*
+		 * Don't use force here, it's convenient if the signal
+		 * can be temporarily blocked.
+		 * This could cause a loop when the user sets SIGBUS
+		 * to SIG_IGN, but hopefully no one will do that?
+		 */
+		si.si_code = BUS_MCEERR_AO;
+		ret = send_sig_info(SIGBUS, &si, t);  /* synchronous? */
+	}
 	if (ret < 0)
 		printk(KERN_INFO "MCE: Error sending signal to %s:%d: %d\n",
 		       t->comm, t->pid, ret);
@@ -338,8 +345,9 @@ static void add_to_kill(struct task_struct *tsk, struct page *p,
  * Also when FAIL is set do a force kill because something went
  * wrong earlier.
  */
-static void kill_procs_ao(struct list_head *to_kill, int doit, int trapno,
-			  int fail, struct page *page, unsigned long pfn)
+static void kill_procs(struct list_head *to_kill, int doit, int trapno,
+			  int fail, struct page *page, unsigned long pfn,
+			  int flags)
 {
 	struct to_kill *tk, *next;
 
@@ -363,8 +371,8 @@ static void kill_procs_ao(struct list_head *to_kill, int doit, int trapno,
 			 * check for that, but we need to tell the
 			 * process anyways.
 			 */
-			else if (kill_proc_ao(tk->tsk, tk->addr, trapno,
-					      pfn, page) < 0)
+			else if (kill_proc(tk->tsk, tk->addr, trapno,
+					      pfn, page, flags) < 0)
 				printk(KERN_ERR
 		"MCE %#lx: Cannot send advisory machine check signal to %s:%d\n",
 					pfn, tk->tsk->comm, tk->tsk->pid);
@@ -844,7 +852,7 @@ static int page_action(struct page_state *ps, struct page *p,
  * the pages and send SIGBUS to the processes if the data was dirty.
  */
 static int hwpoison_user_mappings(struct page *p, unsigned long pfn,
-				  int trapno)
+				  int trapno, int flags)
 {
 	enum ttu_flags ttu = TTU_UNMAP | TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS;
 	struct address_space *mapping;
@@ -962,8 +970,8 @@ static int hwpoison_user_mappings(struct page *p, unsigned long pfn,
 	 * use a more force-full uncatchable kill to prevent
 	 * any accesses to the poisoned memory.
 	 */
-	kill_procs_ao(&tokill, !!PageDirty(ppage), trapno,
-		      ret != SWAP_SUCCESS, p, pfn);
+	kill_procs(&tokill, !!PageDirty(ppage), trapno,
+		      ret != SWAP_SUCCESS, p, pfn, flags);
 
 	return ret;
 }
@@ -1148,7 +1156,7 @@ int memory_failure(unsigned long pfn, int trapno, int flags)
 	 * Now take care of user space mappings.
 	 * Abort on fail: __delete_from_page_cache() assumes unmapped page.
 	 */
-	if (hwpoison_user_mappings(p, pfn, trapno) != SWAP_SUCCESS) {
+	if (hwpoison_user_mappings(p, pfn, trapno, flags) != SWAP_SUCCESS) {
 		printk(KERN_ERR "MCE %#lx: cannot unmap page, give up\n", pfn);
 		res = -EBUSY;
 		goto out;
-- 
1.7.3.1

[PATCH 3/6] x86/mce: Create helper function to save addr/misc when needed

[Tony Luck]

The MCI_STATUS_MISCV and MCI_STATUS_ADDRV bits in the bank status
registers define whether the MISC and ADDR registers respectively
contain valid data - provide a helper function to check these bits
and read the registers when needed.

In addition, processors that support software error recovery (as
indicated by the MCG_SER_P bit in the MCG_CAP register) may include
some undefined bits in the ADDR register - mask these out.

Acked-by: Borislav Petkov <bp@amd64.org>
Signed-off-by: Tony Luck <tony.luck@intel.com>
---
 arch/x86/kernel/cpu/mcheck/mce.c |   31 +++++++++++++++++++++++--------
 1 files changed, 23 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index 1a08ce5..2f1c200 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -492,6 +492,27 @@ static void mce_report_event(struct pt_regs *regs)
 	irq_work_queue(&__get_cpu_var(mce_irq_work));
 }
 
+/*
+ * Read ADDR and MISC registers.
+ */
+static void mce_read_aux(struct mce *m, int i)
+{
+	if (m->status & MCI_STATUS_MISCV)
+		m->misc = mce_rdmsrl(MSR_IA32_MCx_MISC(i));
+	if (m->status & MCI_STATUS_ADDRV) {
+		m->addr = mce_rdmsrl(MSR_IA32_MCx_ADDR(i));
+
+		/*
+		 * Mask the reported address by the reported granularity.
+		 */
+		if (mce_ser && (m->status & MCI_STATUS_MISCV)) {
+			u8 shift = MCI_MISC_ADDR_LSB(m->misc);
+			m->addr >>= shift;
+			m->addr <<= shift;
+		}
+	}
+}
+
 DEFINE_PER_CPU(unsigned, mce_poll_count);
 
 /*
@@ -542,10 +563,7 @@ void machine_check_poll(enum mcp_flags flags, mce_banks_t *b)
 		    (m.status & (mce_ser ? MCI_STATUS_S : MCI_STATUS_UC)))
 			continue;
 
-		if (m.status & MCI_STATUS_MISCV)
-			m.misc = mce_rdmsrl(MSR_IA32_MCx_MISC(i));
-		if (m.status & MCI_STATUS_ADDRV)
-			m.addr = mce_rdmsrl(MSR_IA32_MCx_ADDR(i));
+		mce_read_aux(&m, i);
 
 		if (!(flags & MCP_TIMESTAMP))
 			m.tsc = 0;
@@ -981,10 +999,7 @@ void do_machine_check(struct pt_regs *regs, long error_code)
 		if (severity == MCE_AR_SEVERITY)
 			kill_it = 1;
 
-		if (m.status & MCI_STATUS_MISCV)
-			m.misc = mce_rdmsrl(MSR_IA32_MCx_MISC(i));
-		if (m.status & MCI_STATUS_ADDRV)
-			m.addr = mce_rdmsrl(MSR_IA32_MCx_ADDR(i));
+		mce_read_aux(&m, i);
 
 		/*
 		 * Action optional error. Queue address for later processing.
-- 
1.7.3.1

[PATCH 4/6] x86/mce: Add mechanism to safely save information in MCE handler

[Tony Luck]

Machine checks on Intel cpus interrupt execution on all cpus, regardless
of interrupt masking.  We have a need to save some data about the cause
of the machine check (physical address) in the machine check handler that
can be retrieved later to attempt recovery in a more flexible execution
state.

Signed-off-by: Tony Luck <tony.luck@intel.com>
---
 arch/x86/kernel/cpu/mcheck/mce.c |   43 ++++++++++++++++++++++++++++++++++++++
 1 files changed, 43 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index 2f1c200..e1579c5 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -887,6 +887,49 @@ static void mce_clear_state(unsigned long *toclear)
 }
 
 /*
+ * Need to save faulting physical address associated with a process
+ * in the machine check handler some place where we can grab it back
+ * later in mce_notify_process()
+ */
+#define	MCE_INFO_MAX	16
+
+struct mce_info {
+	atomic_t		inuse;
+	struct task_struct	*t;
+	__u64			paddr;
+} mce_info[MCE_INFO_MAX];
+
+static void mce_save_info(__u64 addr)
+{
+	struct mce_info *mi;
+
+	for (mi = mce_info; mi < &mce_info[MCE_INFO_MAX]; mi++) {
+		if (atomic_cmpxchg(&mi->inuse, 0, 1) == 0) {
+			mi->t = current;
+			mi->paddr = addr;
+			return;
+		}
+	}
+
+	mce_panic("Too many concurrent recoverable errors", NULL, NULL);
+}
+
+static struct mce_info *mce_find_info(void)
+{
+	struct mce_info *mi;
+
+	for (mi = mce_info; mi < &mce_info[MCE_INFO_MAX]; mi++)
+		if (atomic_read(&mi->inuse) && mi->t == current)
+			return mi;
+	return NULL;
+}
+
+static void mce_clear_info(struct mce_info *mi)
+{
+	atomic_set(&mi->inuse, 0);
+}
+
+/*
  * The actual machine check handler. This only handles real
  * exceptions when something got corrupted coming in through int 18.
  *
-- 
1.7.3.1

[PATCH 1/6] HWPOISON: Clean up memory_failure() vs. __memory_failure()

[Tony Luck]

There is only one caller of memory_failure(), all other users call
__memory_failure() and pass in the flags argument explicitly. The
lone user of memory_failure() will soon need to pass flags too.

Add flags argument to the callsite in mce.c. Delete the old memory_failure()
function, and then rename __memory_failure() without the leading "__".

Provide clearer message when action optional memory errors are ignored.

Acked-by: Borislav Petkov <bp@amd64.org>
Signed-off-by: Tony Luck <tony.luck@intel.com>
---
 arch/x86/kernel/cpu/mcheck/mce.c |   12 ++++++---
 drivers/base/memory.c            |    2 +-
 include/linux/mm.h               |    3 +-
 mm/hwpoison-inject.c             |    4 +-
 mm/madvise.c                     |    2 +-
 mm/memory-failure.c              |   46 +++++++++++++++++--------------------
 6 files changed, 34 insertions(+), 35 deletions(-)

diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index 2af127d..1a08ce5 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -1046,11 +1046,15 @@ out:
 }
 EXPORT_SYMBOL_GPL(do_machine_check);
 
-/* dummy to break dependency. actual code is in mm/memory-failure.c */
-void __attribute__((weak)) memory_failure(unsigned long pfn, int vector)
+#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);
+	printk(KERN_ERR "Uncorrected memory error in page 0x%lx ignored\n"
+		"Rebuild kernel with CONFIG_MEMORY_FAILURE=y for smarter handling\n", pfn);
+
+	return 0;
 }
+#endif
 
 /*
  * Called after mce notification in process context. This code
@@ -1068,7 +1072,7 @@ void mce_notify_process(void)
 	unsigned long pfn;
 	mce_notify_irq();
 	while (mce_ring_get(&pfn))
-		memory_failure(pfn, MCE_VECTOR);
+		memory_failure(pfn, MCE_VECTOR, 0);
 }
 
 static void mce_process_work(struct work_struct *dummy)
diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index 8272d92..9a92444 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -474,7 +474,7 @@ store_hard_offline_page(struct class *class,
 	if (strict_strtoull(buf, 0, &pfn) < 0)
 		return -EINVAL;
 	pfn >>= PAGE_SHIFT;
-	ret = __memory_failure(pfn, 0, 0);
+	ret = memory_failure(pfn, 0, 0);
 	return ret ? ret : count;
 }
 
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 4baadd1..bcc5234 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1607,8 +1607,7 @@ void vmemmap_populate_print_last(void);
 enum mf_flags {
 	MF_COUNT_INCREASED = 1 << 0,
 };
-extern void memory_failure(unsigned long pfn, int trapno);
-extern int __memory_failure(unsigned long pfn, int trapno, int flags);
+extern int memory_failure(unsigned long pfn, int trapno, int flags);
 extern void memory_failure_queue(unsigned long pfn, int trapno, int flags);
 extern int unpoison_memory(unsigned long pfn);
 extern int sysctl_memory_failure_early_kill;
diff --git a/mm/hwpoison-inject.c b/mm/hwpoison-inject.c
index c7fc7fd..cc448bb 100644
--- a/mm/hwpoison-inject.c
+++ b/mm/hwpoison-inject.c
@@ -45,7 +45,7 @@ static int hwpoison_inject(void *data, u64 val)
 	 * do a racy check with elevated page count, to make sure PG_hwpoison
 	 * will only be set for the targeted owner (or on a free page).
 	 * We temporarily take page lock for try_get_mem_cgroup_from_page().
-	 * __memory_failure() will redo the check reliably inside page lock.
+	 * memory_failure() will redo the check reliably inside page lock.
 	 */
 	lock_page(hpage);
 	err = hwpoison_filter(hpage);
@@ -55,7 +55,7 @@ static int hwpoison_inject(void *data, u64 val)
 
 inject:
 	printk(KERN_INFO "Injecting memory failure at pfn %lx\n", pfn);
-	return __memory_failure(pfn, 18, MF_COUNT_INCREASED);
+	return memory_failure(pfn, 18, MF_COUNT_INCREASED);
 }
 
 static int hwpoison_unpoison(void *data, u64 val)
diff --git a/mm/madvise.c b/mm/madvise.c
index 74bf193..f5ab745 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -251,7 +251,7 @@ static int madvise_hwpoison(int bhv, unsigned long start, unsigned long end)
 		printk(KERN_INFO "Injecting memory failure for page %lx at %lx\n",
 		       page_to_pfn(p), start);
 		/* Ignore return value for now */
-		__memory_failure(page_to_pfn(p), 0, MF_COUNT_INCREASED);
+		memory_failure(page_to_pfn(p), 0, MF_COUNT_INCREASED);
 	}
 	return ret;
 }
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 06d3479..ab259bb 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -984,7 +984,25 @@ static void clear_page_hwpoison_huge_page(struct page *hpage)
 		ClearPageHWPoison(hpage + i);
 }
 
-int __memory_failure(unsigned long pfn, int trapno, int flags)
+/**
+ * memory_failure - Handle memory failure of a page.
+ * @pfn: Page Number of the corrupted page
+ * @trapno: Trap number reported in the signal to user space.
+ * @flags: fine tune action taken
+ *
+ * This function is called by the low level machine check code
+ * of an architecture when it detects hardware memory corruption
+ * of a page. It tries its best to recover, which includes
+ * dropping pages, killing processes etc.
+ *
+ * The function is primarily of use for corruptions that
+ * happen outside the current execution context (e.g. when
+ * detected by a background scrubber)
+ *
+ * Must run in process context (e.g. a work queue) with interrupts
+ * enabled and no spinlocks hold.
+ */
+int memory_failure(unsigned long pfn, int trapno, int flags)
 {
 	struct page_state *ps;
 	struct page *p;
@@ -1156,29 +1174,7 @@ out:
 	unlock_page(hpage);
 	return res;
 }
-EXPORT_SYMBOL_GPL(__memory_failure);
-
-/**
- * memory_failure - Handle memory failure of a page.
- * @pfn: Page Number of the corrupted page
- * @trapno: Trap number reported in the signal to user space.
- *
- * This function is called by the low level machine check code
- * of an architecture when it detects hardware memory corruption
- * of a page. It tries its best to recover, which includes
- * dropping pages, killing processes etc.
- *
- * The function is primarily of use for corruptions that
- * happen outside the current execution context (e.g. when
- * detected by a background scrubber)
- *
- * Must run in process context (e.g. a work queue) with interrupts
- * enabled and no spinlocks hold.
- */
-void memory_failure(unsigned long pfn, int trapno)
-{
-	__memory_failure(pfn, trapno, 0);
-}
+EXPORT_SYMBOL_GPL(memory_failure);
 
 #define MEMORY_FAILURE_FIFO_ORDER	4
 #define MEMORY_FAILURE_FIFO_SIZE	(1 << MEMORY_FAILURE_FIFO_ORDER)
@@ -1251,7 +1247,7 @@ static void memory_failure_work_func(struct work_struct *work)
 		spin_unlock_irqrestore(&mf_cpu->lock, proc_flags);
 		if (!gotten)
 			break;
-		__memory_failure(entry.pfn, entry.trapno, entry.flags);
+		memory_failure(entry.pfn, entry.trapno, entry.flags);
 	}
 }
 
-- 
1.7.3.1

[PATCH 5/6] x86/mce: Handle "action required" errors

[Tony Luck]

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>
---
 arch/x86/kernel/cpu/mcheck/mce.c |   95 +++++++++++++++++++++-----------------
 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 e1579c5..56e4e79 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);
-- 
1.7.3.1

[PATCH 6/6] x86/mce: Recognise machine check bank signature for data path error

[Tony Luck]

Action required data path signature is defined in table 15-19 of SDM:

+-----------------------------------------------------------------------------+
| SRAR Error | Valid | OVER | UC | EN | MISCV | ADDRV | PCC | S | AR | MCACOD |
| Data Load  |     1 |    0 |  1 |  1 |     1 |     1 |   0 | 1 |  1 |  0x134 |
+-----------------------------------------------------------------------------+

Recognise this, and pass MCE_AR_SEVERITY code back to do_machine_check() if
we have the action handler configured (CONFIG_MEMORY_FAILURE=y)

Acked-by: Borislav Petkov <bp@amd64.org>
Signed-off-by: Tony Luck <tony.luck@intel.com>
---
 arch/x86/kernel/cpu/mcheck/mce-severity.c |   16 +++++++++++++++-
 1 files changed, 15 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kernel/cpu/mcheck/mce-severity.c b/arch/x86/kernel/cpu/mcheck/mce-severity.c
index 7395d5f..f6c92f9 100644
--- a/arch/x86/kernel/cpu/mcheck/mce-severity.c
+++ b/arch/x86/kernel/cpu/mcheck/mce-severity.c
@@ -54,6 +54,7 @@ static struct severity {
 #define  MASK(x, y)	.mask = x, .result = y
 #define MCI_UC_S (MCI_STATUS_UC|MCI_STATUS_S)
 #define MCI_UC_SAR (MCI_STATUS_UC|MCI_STATUS_S|MCI_STATUS_AR)
+#define	MCI_ADDR (MCI_STATUS_ADDRV|MCI_STATUS_MISCV)
 #define MCACOD 0xffff
 
 	MCESEV(
@@ -102,11 +103,24 @@ static struct severity {
 		SER, BITCLR(MCI_STATUS_S)
 		),
 
-	/* AR add known MCACODs here */
 	MCESEV(
 		PANIC, "Action required with lost events",
 		SER, BITSET(MCI_STATUS_OVER|MCI_UC_SAR)
 		),
+
+	/* known AR MCACODs: */
+#ifdef	CONFIG_MEMORY_FAILURE
+	MCESEV(
+		KEEP, "HT thread notices Action required: data load error",
+		SER, MASK(MCI_STATUS_OVER|MCI_UC_SAR|MCI_ADDR|MCACOD, MCI_UC_SAR|MCI_ADDR|0x0134),
+		MCGMASK(MCG_STATUS_EIPV, 0)
+		),
+	MCESEV(
+		AR, "Action required: data load error",
+		SER, MASK(MCI_STATUS_OVER|MCI_UC_SAR|MCI_ADDR|MCACOD, MCI_UC_SAR|MCI_ADDR|0x0134),
+		USER
+		),
+#endif
 	MCESEV(
 		PANIC, "Action required: unknown MCACOD",
 		SER, MASK(MCI_STATUS_OVER|MCI_UC_SAR, MCI_UC_SAR)
-- 
1.7.3.1