x86, mce: improve mce_get_rip

Assume IP on the stack is valid when either EIPV or RIPV are set.
This influences whether the machine check exception handler decides
to return or panic.

This fixes a test case in the mce-test suite and is more compliant
to the specification.

This currently only makes a difference in a artificial testing
scenario with the mce-test test suite.

Also in addition do not force the EIPV to be valid with the exact
register MSRs, and keep in trust the CS value on stack even if MSR
is available.

[AK: combination of patches from Huang Ying and Hidetoshi Seto, with
new description by me]
[add some description, no code changed - HS]
Signed-off-by: Huang Ying <ying.huang@intel.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

arch/x86/kernel/cpu/mcheck/mce.c

@@ -306,21 +306,22 @@ int mce_available(struct cpuinfo_x86 *c)
 	return cpu_has(c, X86_FEATURE_MCE) && cpu_has(c, X86_FEATURE_MCA);
 }
 
+/*
+ * Get the address of the instruction at the time of the machine check
+ * error.
+ */
 static inline void mce_get_rip(struct mce *m, struct pt_regs *regs)
 {
-	if (regs && (m->mcgstatus & MCG_STATUS_RIPV)) {
+
+	if (regs && (m->mcgstatus & (MCG_STATUS_RIPV|MCG_STATUS_EIPV))) {
 		m->ip = regs->ip;
 		m->cs = regs->cs;
 	} else {
 		m->ip = 0;
 		m->cs = 0;
 	}
-	if (rip_msr) {
-		/* Assume the RIP in the MSR is exact. Is this true? */
-		m->mcgstatus |= MCG_STATUS_EIPV;
+	if (rip_msr)
 		m->ip = mce_rdmsrl(rip_msr);
-		m->cs = 0;
-	}
 }
 
 #ifdef CONFIG_X86_LOCAL_APIC