x86/boot: Drop INVALID_VCPU

Now that NULL will fault at boot, there is no need for a special constant to
signify "current not set up yet".

Since c/s fae249d234 "x86/boot: Rationalise stack handling during early
boot", the BSP cpu_info block is now consistently zero, so drop the adjacent
re-zeroing.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

xen/arch/x86/cpu/mcheck/mce.c

@@ -260,7 +260,7 @@ static int mca_init_global(uint32_t flags, struct mcinfo_global *mig)
                         &mig->mc_coreid, &mig->mc_core_threadid,
                         &mig->mc_apicid, NULL, NULL, NULL);
 
-    if ( curr != INVALID_VCPU )
+    if ( curr )
     {
         mig->mc_domid = curr->domain->domain_id;
         mig->mc_vcpuid = curr->vcpu_id;

xen/arch/x86/domain_page.c

@@ -29,7 +29,7 @@ static inline struct vcpu *mapcache_current_vcpu(void)
      * When current isn't properly set up yet, this is equivalent to
      * running in an idle vCPU (callers must check for NULL).
      */
-    if ( v == INVALID_VCPU )
+    if ( !v )
         return NULL;
 
     /*

xen/arch/x86/setup.c

@@ -707,9 +707,6 @@ void __init noreturn __start_xen(unsigned long mbi_p)
 
     /* Critical region without IDT or TSS.  Any fault is deadly! */
 
-    set_processor_id(0);
-    set_current(INVALID_VCPU); /* debug sanity. */
-    idle_vcpu[0] = current;
     init_shadow_spec_ctrl_state();
 
     percpu_init_areas();

xen/arch/x86/tboot.c

@@ -392,7 +392,7 @@ void tboot_shutdown(uint32_t shutdown_type)
      * During early boot, we can be called by panic before idle_vcpu[0] is
      * setup, but in that case we don't need to change page tables.
      */
-    if ( idle_vcpu[0] != INVALID_VCPU )
+    if ( idle_vcpu[0] )
         write_ptbase(idle_vcpu[0]);
 
     ((void(*)(void))(unsigned long)g_tboot_shared->shutdown_entry)();

xen/include/asm-x86/setup.h

@@ -4,9 +4,6 @@
 #include <xen/multiboot.h>
 #include <asm/numa.h>
 
-/* vCPU pointer used prior to there being a valid one around */
-#define INVALID_VCPU ((struct vcpu *)0xccccccccccccc000UL)
-
 extern const char __2M_text_start[], __2M_text_end[];
 extern const char __2M_rodata_start[], __2M_rodata_end[];
 extern char __2M_init_start[], __2M_init_end[];