[BUGFIX -v2] x86, mce, inject: Make injected mce valid only duringfaked handler call

[Huang Ying]

In the current implementation, injected MCE is valid from the point
the MCE is injected to the point the MCE is processed by the faked
handler call.

This has an undesired side-effect: it is possible for it to be
consumed by real machine_check_poll. This may confuse a real system
error and may confuse the mce test suite.

To fix this, this patch introduces another flag MCJ_VALID to indicate
that the MCE entry is valid for injector but not for the
handler. Another flag, mce.finished is used to indicate the MCE entry
is valid for the handler.

mce.finished is enabled only during faked MCE handler call and
protected by IRQ disabling. This make it impossible for real
machine_check_poll to consume it.

Signed-off-by: Huang Ying <ying.huang@xxxxxxxxx>

v2:
- Revise commit changelog (Thanks Ingo)
- Change naming (XX_BIT for bit definition)

---
 arch/x86/include/asm/mce.h              |   17 +++++++++++------
 arch/x86/kernel/cpu/mcheck/mce-inject.c |   23 ++++++++++++++++-------
 2 files changed, 27 insertions(+), 13 deletions(-)

--- a/arch/x86/include/asm/mce.h
+++ b/arch/x86/include/asm/mce.h
@@ -38,13 +38,18 @@
 #define MCM_ADDR_MEM	 3	/* memory address */
 #define MCM_ADDR_GENERIC 7	/* generic */
 
-#define MCJ_CTX_MASK		3
+#define MCJ_NMI_BROADCAST_BIT	2    /* do NMI broadcasting */
+#define MCJ_EXCEPTION_BIT	3    /* raise as exception */
+#define MCJ_LOADED_BIT		4    /* entry is valid for injector */
+
+#define MCJ_CTX_MASK		0x03
 #define MCJ_CTX(flags)		((flags) & MCJ_CTX_MASK)
-#define MCJ_CTX_RANDOM		0    /* inject context: random */
-#define MCJ_CTX_PROCESS		1    /* inject context: process */
-#define MCJ_CTX_IRQ		2    /* inject context: IRQ */
-#define MCJ_NMI_BROADCAST	4    /* do NMI broadcasting */
-#define MCJ_EXCEPTION		8    /* raise as exception */
+#define MCJ_CTX_RANDOM		0x00    /* inject context: random */
+#define MCJ_CTX_PROCESS		0x01    /* inject context: process */
+#define MCJ_CTX_IRQ		0x02    /* inject context: IRQ */
+#define MCJ_NMI_BROADCAST	(1 << MCJ_NMI_BROADCAST_BIT)
+#define MCJ_EXCEPTION		(1 << MCJ_EXCEPTION_BIT)
+#define MCJ_LOADED		(1 << MCJ_LOADED_BIT)
 
 /* Fields are zero when not available */
 struct mce {
--- a/arch/x86/kernel/cpu/mcheck/mce-inject.c
+++ b/arch/x86/kernel/cpu/mcheck/mce-inject.c
@@ -32,16 +32,16 @@ static void inject_mce(struct mce *m)
 
 	/* Make sure noone reads partially written injectm */
 	i->finished = 0;
+	clear_bit(MCJ_LOADED_BIT, (unsigned long *)&i->inject_flags);
 	mb();
 	m->finished = 0;
-	/* First set the fields after finished */
+	clear_bit(MCJ_LOADED_BIT, (unsigned long *)&m->inject_flags);
 	i->extcpu = m->extcpu;
 	mb();
-	/* Now write record in order, finished last (except above) */
 	memcpy(i, m, sizeof(struct mce));
 	/* Finally activate it */
 	mb();
-	i->finished = 1;
+	set_bit(MCJ_LOADED_BIT, (unsigned long *)&i->inject_flags);
 }
 
 static void raise_poll(struct mce *m)
@@ -51,9 +51,11 @@ static void raise_poll(struct mce *m)
 
 	memset(&b, 0xff, sizeof(mce_banks_t));
 	local_irq_save(flags);
+	m->finished = 1;
 	machine_check_poll(0, &b);
-	local_irq_restore(flags);
 	m->finished = 0;
+	clear_bit(MCJ_LOADED_BIT, (unsigned long *)&m->inject_flags);
+	local_irq_restore(flags);
 }
 
 static void raise_exception(struct mce *m, struct pt_regs *pregs)
@@ -69,9 +71,11 @@ static void raise_exception(struct mce *
 	}
 	/* in mcheck exeception handler, irq will be disabled */
 	local_irq_save(flags);
+	m->finished = 1;
 	do_machine_check(pregs, 0);
-	local_irq_restore(flags);
 	m->finished = 0;
+	clear_bit(MCJ_LOADED_BIT, (unsigned long *)&m->inject_flags);
+	local_irq_restore(flags);
 }
 
 static cpumask_t mce_inject_cpumask;
@@ -89,6 +93,8 @@ static int mce_raise_notify(struct notif
 		raise_exception(m, args->regs);
 	else if (m->status)
 		raise_poll(m);
+	else
+		clear_bit(MCJ_LOADED_BIT, (unsigned long *)&m->inject_flags);
 	return NOTIFY_STOP;
 }
 
@@ -129,7 +135,7 @@ static int raise_local(void)
 		mce_notify_irq();
 		printk(KERN_INFO "Machine check poll done on CPU %d\n", cpu);
 	} else
-		m->finished = 0;
+		clear_bit(MCJ_LOADED_BIT, (unsigned long *)&m->inject_flags);
 
 	return ret;
 }
@@ -152,10 +158,13 @@ static void raise_mce(struct mce *m)
 		cpu_clear(get_cpu(), mce_inject_cpumask);
 		for_each_online_cpu(cpu) {
 			struct mce *mcpu = &per_cpu(injectm, cpu);
-			if (!mcpu->finished ||
+			if (!test_bit(MCJ_LOADED_BIT,
+				      (unsigned long *)&mcpu->inject_flags) ||
 			    MCJ_CTX(mcpu->inject_flags) != MCJ_CTX_RANDOM)
 				cpu_clear(cpu, mce_inject_cpumask);
 		}
+		/* make sure needed data is available on other CPUs */
+		smp_mb();
 		if (!cpus_empty(mce_inject_cpumask))
 			apic->send_IPI_mask(&mce_inject_cpumask, NMI_VECTOR);
 		start = jiffies;


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