MCE: Fix vm86 handling for 32bit mce handler

commit a129a7c8 upstream.

When running on 32bit the mce handler could misinterpret
vm86 mode as ring 0. This can affect whether it does recovery
or not; it was possible to panic when recovery was actually
possible.

Fix this by always forcing vm86 to look like ring 3.
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

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

@@ -389,6 +389,14 @@ static inline void mce_gather_info(struct mce *m, struct pt_regs *regs)
 		if (m->mcgstatus & (MCG_STATUS_RIPV|MCG_STATUS_EIPV)) {
 			m->ip = regs->ip;
 			m->cs = regs->cs;
+
+			/*
+			 * When in VM86 mode make the cs look like ring 3
+			 * always. This is a lie, but it's better than passing
+			 * the additional vm86 bit around everywhere.
+			 */
+			if (v8086_mode(regs))
+				m->cs |= 3;
 		}
 		/* Use accurate RIP reporting if available. */
 		if (rip_msr)