[PATCH 2/2] x86/mce: Add quirk for instruction recovery on SandyBridge processors

[Tony Luck]

Sandy Bridge processors follow the SDM (Vol 3B, Table 15-20) and set
both the RIPV and EIPV bits in the MCG_STATUS register to zero for
machine checks during instruction fetch. This is more than a little
counter-intuitive and means that Linux cannot recover from these
errors. Rather than insert special case code at several places in mce.c
and mce-severity.c, we pretend the EIPV bit was set for just this case
early in processing the machine check.

Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
---
 arch/x86/kernel/cpu/mcheck/mce.c | 43 +++++++++++++++++++++++++++++++++++++---
 1 file changed, 40 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index da27c5d..e65e738 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -102,6 +102,8 @@ DEFINE_PER_CPU(mce_banks_t, mce_poll_banks) = {
 
 static DEFINE_PER_CPU(struct work_struct, mce_work);
 
+static void (*quirk_no_way_out)(int bank, struct mce *m, struct pt_regs *regs);
+
 /*
  * CPU/chipset specific EDAC code can register a notifier call here to print
  * MCE errors in a human-readable form.
@@ -649,14 +651,18 @@ EXPORT_SYMBOL_GPL(machine_check_poll);
  * Do a quick check if any of the events requires a panic.
  * This decides if we keep the events around or clear them.
  */
-static int mce_no_way_out(struct mce *m, char **msg, unsigned long *validp)
+static int mce_no_way_out(struct mce *m, char **msg, unsigned long *validp,
+			  struct pt_regs *regs)
 {
 	int i, ret = 0;
 
 	for (i = 0; i < banks; i++) {
 		m->status = mce_rdmsrl(MSR_IA32_MCx_STATUS(i));
-		if (m->status & MCI_STATUS_VAL)
+		if (m->status & MCI_STATUS_VAL) {
 			__set_bit(i, validp);
+			if (quirk_no_way_out)
+				quirk_no_way_out(i, m, regs);
+		}
 		if (mce_severity(m, tolerant, msg) >= MCE_PANIC_SEVERITY)
 			ret = 1;
 	}
@@ -1039,7 +1045,7 @@ void do_machine_check(struct pt_regs *regs, long error_code)
 	*final = m;
 
 	memset(valid_banks, 0, sizeof(valid_banks));
-	no_way_out = mce_no_way_out(&m, &msg, valid_banks);
+	no_way_out = mce_no_way_out(&m, &msg, valid_banks, regs);
 
 	barrier();
 
@@ -1415,6 +1421,34 @@ static void __mcheck_cpu_init_generic(void)
 	}
 }
 
+/*
+ * During IFU recovery Sandy Bridge -EP4S processors set the RIPV and
+ * EIPV bits in MCG_STATUS to zero on the affected logical processor (SDM
+ * Vol 3B Table 15-20). But this confuses both the code that determines
+ * whether the machine check occurred in kernel or user mode, and also
+ * the severity assessment code. Pretend that EIPV was set, and take the
+ * ip/cs values from the pt_regs that mce_gather_info() ignored earlier.
+ */
+static void quirk_sandybridge_ifu(int bank, struct mce *m, struct pt_regs *regs)
+{
+	if (bank != 0)
+		return;
+	if ((m->mcgstatus & (MCG_STATUS_EIPV|MCG_STATUS_RIPV)) != 0)
+		return;
+	if ((m->status & (MCI_STATUS_OVER|MCI_STATUS_UC|
+		          MCI_STATUS_EN|MCI_STATUS_MISCV|MCI_STATUS_ADDRV|
+			  MCI_STATUS_PCC|MCI_STATUS_S|MCI_STATUS_AR|
+			  MCACOD)) !=
+			 (MCI_STATUS_UC|MCI_STATUS_EN|
+			  MCI_STATUS_MISCV|MCI_STATUS_ADDRV|MCI_STATUS_S|
+			  MCI_STATUS_AR|MCACOD_INSTR))
+		return;
+
+	m->mcgstatus |= MCG_STATUS_EIPV;
+	m->ip = regs->ip;
+	m->cs = regs->cs;
+}
+
 /* Add per CPU specific workarounds here */
 static int __cpuinit __mcheck_cpu_apply_quirks(struct cpuinfo_x86 *c)
 {
@@ -1512,6 +1546,9 @@ static int __cpuinit __mcheck_cpu_apply_quirks(struct cpuinfo_x86 *c)
 		 */
 		if (c->x86 == 6 && c->x86_model <= 13 && mce_bootlog < 0)
 			mce_bootlog = 0;
+
+		if (c->x86 == 6 && c->x86_model == 45)
+			quirk_no_way_out = quirk_sandybridge_ifu;
 	}
 	if (monarch_timeout < 0)
 		monarch_timeout = 0;
-- 
1.7.10.2.552.gaa3bb87

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