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 bd809af16e3ab 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: bd809af16e3ab "x86: Enable PAT to use cache mode translation tables"
Reported-and-tested-by: Jongman Heo <jongman.heo@samsung.com>
Acked-by: Alok N Kataria <akataria@vmware.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Link: http://lkml.kernel.org/r/1421039745-14335-1-git-send-email-jgross@suse.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 6 insertions, 1 deletions

diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index edf299c8ff6c..7ac68698406c 100644
--- a/arch/x86/mm/pat.c
+++ b/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);