x86/mm/32: Load a sane CR3 before cpu_init() on secondary CPUs

For unknown historical reasons (i.e. Borislav doesn't recall),
32-bit kernels invoke cpu_init() on secondary CPUs with
initial_page_table loaded into CR3.  Then they set
current->active_mm to &init_mm and call enter_lazy_tlb() before
fixing CR3.  This means that the x86 TLB code gets invoked while CR3
is inconsistent, and, with the improved PCID sanity checks I added,
we warn.

Fix it by loading swapper_pg_dir (i.e. init_mm.pgd) earlier.

Reported-by: Paul Menzel <[email protected]>
Reported-by: Pavel Machek <[email protected]>
Signed-off-by: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Fixes: 72c0098 ("x86/mm: Reinitialize TLB state on hotplug and resume")
Link: http://lkml.kernel.org/r/30cdfea504682ba3b9012e77717800a91c22097f.1505663533.git.luto@kernel.org
Signed-off-by: Ingo Molnar <[email protected]>

Author: amluto

arch/x86/kernel/smpboot.c

@@ -232,19 +232,20 @@ static void notrace start_secondary(void *unused)
 	 */
 	if (boot_cpu_has(X86_FEATURE_PCID))
 		__write_cr4(__read_cr4() | X86_CR4_PCIDE);
-	cpu_init();
-	x86_cpuinit.early_percpu_clock_init();
-	preempt_disable();
-	smp_callin();
-
-	enable_start_cpu0 = 0;
 
 #ifdef CONFIG_X86_32
 	/* switch away from the initial page table */
 	load_cr3(swapper_pg_dir);
 	__flush_tlb_all();
 #endif
 
+	cpu_init();
+	x86_cpuinit.early_percpu_clock_init();
+	preempt_disable();
+	smp_callin();
+
+	enable_start_cpu0 = 0;
+
 	/* otherwise gcc will move up smp_processor_id before the cpu_init */
 	barrier();
 	/*