x86/mm/32: Initialize the CR4 shadow before __flush_tlb_all()

On 32-bit kernels, __flush_tlb_all() may have read the CR4 shadow before the
initialization of CR4 shadow in cpu_init().

Fix it by adding an explicit cr4_init_shadow() call into start_secondary()
which is the first function called on non-boot SMP CPUs - ahead of the
__flush_tlb_all() call.

( This is somewhat of a layering violation, but start_secondary() does
  CR4 bootstrap in the PCID case anyway. )

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Link: http://lkml.kernel.org/r/b07b6ae9-4b57-4b40-b9bc-50c2c67f1d91@default
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/smpboot.c

@@ -221,6 +221,11 @@ static void notrace start_secondary(void *unused)
 #ifdef CONFIG_X86_32
 	/* switch away from the initial page table */
 	load_cr3(swapper_pg_dir);
+	/*
+	 * Initialize the CR4 shadow before doing anything that could
+	 * try to read it.
+	 */
+	cr4_init_shadow();
 	__flush_tlb_all();
 #endif
 	load_current_idt();