Revert "x86/PAT: Fix Xorg regression on CPUs that don't support PAT"

This reverts commit cbed27cd.

As Andy Lutomirski observed:

 "I think this patch is bogus. pat_enabled() sure looks like it's
  supposed to return true if PAT is *enabled*, and these days PAT is
  'enabled' even if there's no HW PAT support."
Reported-by: NBernhard Held <berny156@gmx.de>
Reported-by: NChris Wilson <chris@chris-wilson.co.uk>
Acked-by: NAndy Lutomirski <luto@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luis R. Rodriguez <mcgrof@suse.com>
Cc: Mikulas Patocka <mpatocka@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Toshi Kani <toshi.kani@hp.com>
Cc: stable@vger.kernel.org # v4.2+
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NIngo Molnar <mingo@kernel.org>

arch/x86/mm/pat.c

@@ -65,11 +65,9 @@ static int __init nopat(char *str)
 }
 early_param("nopat", nopat);
 
-static bool __read_mostly __pat_initialized = false;
-
 bool pat_enabled(void)
 {
-	return __pat_initialized;
+	return !!__pat_enabled;
 }
 EXPORT_SYMBOL_GPL(pat_enabled);
 
@@ -227,14 +225,13 @@ static void pat_bsp_init(u64 pat)
 	}
 
 	wrmsrl(MSR_IA32_CR_PAT, pat);
-	__pat_initialized = true;
 
 	__init_cache_modes(pat);
 }
 
 static void pat_ap_init(u64 pat)
 {
-	if (!this_cpu_has(X86_FEATURE_PAT)) {
+	if (!boot_cpu_has(X86_FEATURE_PAT)) {
 		/*
 		 * If this happens we are on a secondary CPU, but switched to
 		 * PAT on the boot CPU. We have no way to undo PAT.
@@ -309,7 +306,7 @@ void pat_init(void)
 	u64 pat;
 	struct cpuinfo_x86 *c = &boot_cpu_data;
 
-	if (!__pat_enabled) {
+	if (!pat_enabled()) {
 		init_cache_modes();
 		return;
 	}