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 <[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]>

diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index edf299c8ff6c774dea8116092a41b15102d9cf1c..7ac68698406c3b35e5ce0b0e98c73c5441e869a3 100644 (file)
--- 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);