xen: rework xen_pv_domain()

Rework xen_pv_domain() to no longer use the xen_domain_type variable,
but the artificial X86_FEATURE_XENPV cpu feature.

On non-x86 architectures xen_pv_domain() can be defined as "0".

This has the advantage that a kernel not built with CONFIG_XEN_PV
will be smaller due to dead code elimination.

Set the X86_FEATURE_XENPV feature very early, as xen_pv_domain() is
used rather early, too.

Reviewed-by: Jason Andryuk <[e-mail]>
Signed-off-by: Juergen Gross <[e-mail]>
Message-ID: <[e-mail]>

arch/x86/xen/enlighten_pv.c

···
 
 static void __init xen_init_capabilities(void)
 {
-	setup_force_cpu_cap(X86_FEATURE_XENPV);
 	setup_clear_cpu_cap(X86_FEATURE_DCA);
 	setup_clear_cpu_cap(X86_FEATURE_APERFMPERF);
 	setup_clear_cpu_cap(X86_FEATURE_MTRR);
···
 			JMP32_INSN_SIZE);
 
 	xen_domain_type = XEN_PV_DOMAIN;
+	setup_force_cpu_cap(X86_FEATURE_XENPV);
 	xen_start_flags = xen_start_info->flags;
 	/* Interrupts are guaranteed to be off initially. */
 	early_boot_irqs_disabled = true;

include/xen/xen.h

···
 #define xen_pvh			0
 #endif
 
+#ifdef CONFIG_X86
+#include <asm/cpufeature.h>
+
+#define xen_pv_domain()		(cpu_feature_enabled(X86_FEATURE_XENPV))
+#else
+#define xen_pv_domain()		0
+#endif
+
 #define xen_domain()		(xen_domain_type != XEN_NATIVE)
-#define xen_pv_domain()		(xen_domain_type == XEN_PV_DOMAIN)
 #define xen_hvm_domain()	(xen_domain_type == XEN_HVM_DOMAIN)
 #define xen_pvh_domain()	(xen_pvh)