Amd64 init_secondary() calls initializecpu() while curthread is still

not properly set up. r199067 added the call to TUNABLE_INT_FETCH() to
initializecpu() that results in hang because AP are started when kernel
environment is already dynamic and thus needs to acquire mutex, that is
too early in AP start sequence to work.

Extract the code that should be executed only once, because it sets
up global variables, from initializecpu() to initializecpucache(),
and call the later only from hammer_time() executed on BSP. Now,
TUNABLE_INT_FETCH() is done only once at BSP at the early boot stage.

In collaboration with:	Mykola Dzham <freebsd levsha org ua>
Reviewed by:	jhb
Tested by:	ed, battlez

sys/amd64/amd64/initcpu.c

@@ -163,6 +163,11 @@ initializecpu(void)
 	    CPUID_TO_FAMILY(cpu_id) == 0x6 &&
 	    CPUID_TO_MODEL(cpu_id) >= 0xf)
 		init_via();
+}
+
+void
+initializecpucache()
+{
 
 	/*
 	 * CPUID with %eax = 1, %ebx returns

sys/amd64/amd64/machdep.c

@@ -1663,6 +1663,7 @@ hammer_time(u_int64_t modulep, u_int64_t physfree)
 
 	identify_cpu();		/* Final stage of CPU initialization */
 	initializecpu();	/* Initialize CPU registers */
+	initializecpucache();
 
 	/* make an initial tss so cpu can get interrupt stack on syscall! */
 	common_tss[0].tss_rsp0 = thread0.td_kstack + \

sys/amd64/include/md_var.h

@@ -89,6 +89,7 @@ void	gs_load_fault(void) __asm(__STRING(gs_load_fault));
 void	dump_add_page(vm_paddr_t);
 void	dump_drop_page(vm_paddr_t);
 void	initializecpu(void);
+void	initializecpucache(void);
 void	fillw(int /*u_short*/ pat, void *base, size_t cnt);
 void	fpstate_drop(struct thread *td);
 int	is_physical_memory(vm_paddr_t addr);