x86/traps: Move traps_init() earlier on boot

We wish to make use of opt_fred earlier on boot, which involves moving
traps_init() earlier, but this comes with several ordering complications.

The feature word containing FRED needs collecting in early_cpu_init(), and
legacy_syscall_init() cannot be moved that early because it relies on the
stubs being allocated, yet must be called ahead of cpu_init() so the SYSCALL
linkage MSRs are set up before being cached.

Delaying legacy_syscall_init() is easy enough based on a system_state check.
Reuse bsp_traps_reinit() to cause a call to legacy_syscall_init() to occur at
the same point as previously.

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

xen/arch/x86/cpu/common.c

@@ -407,7 +407,9 @@ void __init early_cpu_init(bool verbose)
 		}
 
 		if (max_subleaf >= 1)
-			cpuid_count(7, 1, &eax, &ebx, &ecx,
+			cpuid_count(7, 1,
+                                    &c->x86_capability[FEATURESET_7a1],
+                                    &ebx, &ecx,
 				    &c->x86_capability[FEATURESET_7d1]);
 	}
 

xen/arch/x86/setup.c

@@ -1386,6 +1386,8 @@ void asmlinkage __init noreturn __start_xen(void)
     else
         panic("Bootloader provided no memory information\n");
 
+    traps_init();
+
     /* Choose shadow stack early, to set infrastructure up appropriately. */
     if ( !boot_cpu_has(X86_FEATURE_CET_SS) )
         opt_xen_shstk = 0;
@@ -2078,7 +2080,7 @@ void asmlinkage __init noreturn __start_xen(void)
                                            &this_cpu(stubs).mfn);
     BUG_ON(!this_cpu(stubs.addr));
 
-    traps_init(); /* Needs stubs allocated, must be before presmp_initcalls. */
+    bsp_traps_reinit(); /* Needs stubs allocated, must be before presmp_initcalls. */
 
     cpu_init();
 

xen/arch/x86/traps-setup.c

@@ -346,6 +346,10 @@ void __init traps_init(void)
 
 /*
  * Re-initialise all state referencing the early-boot stack.
+ *
+ * This is called twice during boot, first to ensure legacy_syscall_init() has
+ * run (deferred from earlier), and second when the virtual address of the BSP
+ * stack changes.
  */
 void __init bsp_traps_reinit(void)
 {
@@ -359,7 +363,13 @@ void __init bsp_traps_reinit(void)
  */
 void percpu_traps_init(void)
 {
-    legacy_syscall_init();
+    /*
+     * Skip legacy_syscall_init() at early boot.  It requires the stubs being
+     * allocated, limiting the placement of the traps_init() call, and gets
+     * re-done anyway by bsp_traps_reinit().
+     */
+    if ( system_state > SYS_STATE_early_boot )
+        legacy_syscall_init();
 
     if ( cpu_has_xen_lbr )
         wrmsrl(MSR_IA32_DEBUGCTLMSR, IA32_DEBUGCTLMSR_LBR);