x86/AMD: Apply erratum 665 on machines without a BIOS fix

commit d1992996 upstream.

AMD F12h machines have an erratum which can cause DIV/IDIV to behave
unpredictably. The workaround is to set MSRC001_1029[31] but sometimes
there is no BIOS update containing that workaround so let's do it
ourselves unconditionally. It is simple enough.

[ Borislav: Wrote commit message. ]
Signed-off-by: Emanuel Czirai <icanrealizeum@gmail.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Yaowu Xu <yaowu@google.com>
Link: http://lkml.kernel.org/r/20160902053550.18097-1-bp@alien8.deSigned-off-by: Thomas Gleixner <tglx@linutronix.de>
[bwh: Backported to 3.16:
 - Add an if-statement to init_amd() in place of the switch
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

arch/x86/kernel/cpu/amd.c

@@ -522,6 +522,17 @@ static const int amd_erratum_383[];
 static const int amd_erratum_400[];
 static bool cpu_has_amd_erratum(struct cpuinfo_x86 *cpu, const int *erratum);
 
+#define MSR_AMD64_DE_CFG	0xC0011029
+
+static void init_amd_ln(struct cpuinfo_x86 *c)
+{
+	/*
+	 * Apply erratum 665 fix unconditionally so machines without a BIOS
+	 * fix work.
+	 */
+	msr_set_bit(MSR_AMD64_DE_CFG, 31);
+}
+
 static void init_amd(struct cpuinfo_x86 *c)
 {
 	u32 dummy;
@@ -614,6 +625,9 @@ static void init_amd(struct cpuinfo_x86 *c)
 		}
 	}
 
+	if (c->x86 == 0x12)
+		init_amd_ln(c);
+
 	/* re-enable TopologyExtensions if switched off by BIOS */
 	if ((c->x86 == 0x15) &&
 	    (c->x86_model >= 0x10) && (c->x86_model <= 0x1f) &&