x86: Don't rely on VMWare emulating PAT MSR correctly

VMWare seems not to emulate the PAT MSR correctly: reaeding
MSR_IA32_CR_PAT returns 0 even after writing another value to it.

Commit bd809af triggers this VMWare bug when the kernel is
booted as a VMWare guest.

Detect this bug and don't use the read value if it is 0.

Fixes: bd809af "x86: Enable PAT to use cache mode translation tables"
Reported-and-tested-by: Jongman Heo <[email protected]>
Acked-by: Alok N Kataria <[email protected]>
Signed-off-by: Juergen Gross <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Thomas Gleixner <[email protected]>

Author: jgross1

arch/x86/mm/pat.c

@@ -234,8 +234,13 @@ void pat_init(void)
 	      PAT(4, WB) | PAT(5, WC) | PAT(6, UC_MINUS) | PAT(7, UC);
 
 	/* Boot CPU check */
-	if (!boot_pat_state)
+	if (!boot_pat_state) {
 		rdmsrl(MSR_IA32_CR_PAT, boot_pat_state);
+		if (!boot_pat_state) {
+			pat_disable("PAT read returns always zero, disabled.");
+			return;
+		}
+	}
 
 	wrmsrl(MSR_IA32_CR_PAT, pat);