[tip:x86/urgent] x86/boot: Fix another __read_cr4() case on 486

[tip-bot for Andy Lutomirski]

Commit-ID:  192d1dccbfc5b901b66527df9df80304693cf06e
Gitweb:     http://git.kernel.org/tip/192d1dccbfc5b901b66527df9df80304693cf06e
Author:     Andy Lutomirski <luto@xxxxxxxxxx>
AuthorDate: Thu, 29 Sep 2016 12:48:11 -0700
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Fri, 30 Sep 2016 12:37:40 +0200

x86/boot: Fix another __read_cr4() case on 486

The condition for reading CR4 was wrong: there are some CPUs with
CPUID but not CR4.  Rather than trying to make the condition exact,
use __read_cr4_safe().

Fixes: 18bc7bd523e0 ("x86/boot: Synchronize trampoline_cr4_features and mmu_cr4_features directly")
Reported-by: david@xxxxxxxxxxxxxx
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
Reviewed-by: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Link: http://lkml.kernel.org/r/8c453a61c4f44ab6ff43c29780ba04835234d2e5.1475178369.git.luto@xxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

---
 arch/x86/kernel/setup.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 0fa60f5..98c9cd6 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -1137,9 +1137,7 @@ void __init setup_arch(char **cmdline_p)
 	 * auditing all the early-boot CR4 manipulation would be needed to
 	 * rule it out.
 	 */
-	if (boot_cpu_data.cpuid_level >= 0)
-		/* A CPU has %cr4 if and only if it has CPUID. */
-		mmu_cr4_features = __read_cr4();
+	mmu_cr4_features = __read_cr4_safe();
 
 	memblock_set_current_limit(get_max_mapped());