x86/xsave: simplify xcomp_bv initialization

This simplifies a number of pointless conditionals: Bits 0 and 1 of
xcomp_bv don't matter anyway, and as long as none of bits 2..62 are
set, setting bit 63 is pointless too unless XSAVES is in use.

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

xen/arch/x86/domain.c

@@ -922,9 +922,8 @@ int arch_set_info_guest(
         if ( v->arch.xsave_area )
         {
             v->arch.xsave_area->xsave_hdr.xstate_bv = XSTATE_FP_SSE;
-            if ( cpu_has_xsaves || cpu_has_xsavec )
-                v->arch.xsave_area->xsave_hdr.xcomp_bv = XSTATE_FP_SSE |
-                                                         XSTATE_COMPACTION_ENABLED;
+            v->arch.xsave_area->xsave_hdr.xcomp_bv =
+                cpu_has_xsaves ? XSTATE_COMPACTION_ENABLED : 0;
         }
     }
     else if ( v->arch.xsave_area )

xen/arch/x86/hvm/hvm.c

@@ -2110,9 +2110,8 @@ static int hvm_load_cpu_ctxt(struct domain *d, hvm_domain_context_t *h)
             struct xsave_struct *xsave_area = v->arch.xsave_area;
 
             xsave_area->xsave_hdr.xstate_bv = XSTATE_FP_SSE;
-            if ( cpu_has_xsaves || cpu_has_xsavec )
-                xsave_area->xsave_hdr.xcomp_bv = XSTATE_FP_SSE |
-                                                 XSTATE_COMPACTION_ENABLED;
+            xsave_area->xsave_hdr.xcomp_bv =
+                cpu_has_xsaves ? XSTATE_COMPACTION_ENABLED : 0;
         }
     }
 
@@ -5476,9 +5475,8 @@ void hvm_vcpu_reset_state(struct vcpu *v, uint16_t cs, uint16_t ip)
     if ( v->arch.xsave_area )
     {
         v->arch.xsave_area->xsave_hdr.xstate_bv = XSTATE_FP;
-        if ( cpu_has_xsaves || cpu_has_xsavec )
-            v->arch.xsave_area->xsave_hdr.xcomp_bv = XSTATE_FP |
-                                                     XSTATE_COMPACTION_ENABLED;
+        v->arch.xsave_area->xsave_hdr.xcomp_bv =
+            cpu_has_xsaves ? XSTATE_COMPACTION_ENABLED : 0;
     }
 
     v->arch.vgc_flags = VGCF_online;

xen/arch/x86/i387.c

@@ -272,7 +272,7 @@ int vcpu_init_fpu(struct vcpu *v)
     if ( v->arch.xsave_area )
     {
         v->arch.fpu_ctxt = &v->arch.xsave_area->fpu_sse;
-        if ( cpu_has_xsaves || cpu_has_xsavec )
+        if ( cpu_has_xsaves )
             v->arch.xsave_area->xsave_hdr.xcomp_bv = XSTATE_COMPACTION_ENABLED;
     }
     else