This was used by VMX only, and the intended VMCS write can as well
happen from vmx_set_tsc_offset(), invoked (directly or indirectly)
almost immediately after the present call sites of the hook.
vmx_set_tsc_offset() isn't invoked frequently elsewhere, so the extra
VMCS write shouldn't raise performance concerns.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>

--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -1086,9 +1086,6 @@ static int cf_check hvm_load_cpu_ctxt(st
     v->arch.hvm.guest_cr[2] = ctxt.cr2;
     hvm_update_guest_cr(v, 2);
 
-    if ( hvm_funcs.tsc_scaling.setup )
-        alternative_vcall(hvm_funcs.tsc_scaling.setup, v);
-
     v->arch.msrs->tsc_aux = ctxt.msr_tsc_aux;
 
     hvm_set_guest_tsc_fixed(v, ctxt.tsc, d->arch.hvm.sync_tsc);
@@ -4033,9 +4030,6 @@ void hvm_vcpu_reset_state(struct vcpu *v
     hvm_set_segment_register(v, x86_seg_gdtr, &reg);
     hvm_set_segment_register(v, x86_seg_idtr, &reg);
 
-    if ( hvm_funcs.tsc_scaling.setup )
-        alternative_vcall(hvm_funcs.tsc_scaling.setup, v);
-
     /* Sync AP's TSC with BSP's. */
     v->arch.hvm.cache_tsc_offset =
         v->domain->vcpu[0]->arch.hvm.cache_tsc_offset;
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -1454,20 +1454,13 @@ static void cf_check vmx_handle_cd(struc
     }
 }
 
-static void cf_check vmx_setup_tsc_scaling(struct vcpu *v)
-{
-    if ( v->domain->arch.vtsc )
-        return;
-
-    vmx_vmcs_enter(v);
-    __vmwrite(TSC_MULTIPLIER, hvm_tsc_scaling_ratio(v->domain));
-    vmx_vmcs_exit(v);
-}
-
 static void cf_check vmx_set_tsc_offset(struct vcpu *v, u64 offset, u64 at_tsc)
 {
     vmx_vmcs_enter(v);
 
+    if ( !v->domain->arch.vtsc && cpu_has_vmx_tsc_scaling )
+        __vmwrite(TSC_MULTIPLIER, hvm_tsc_scaling_ratio(v->domain));
+
     if ( nestedhvm_vcpu_in_guestmode(v) )
         offset += nvmx_get_tsc_offset(v);
 
@@ -3031,10 +3024,7 @@ const struct hvm_function_table * __init
     }
 
     if ( cpu_has_vmx_tsc_scaling )
-    {
         vmx_function_table.tsc_scaling.ratio_frac_bits = 48;
-        vmx_function_table.tsc_scaling.setup = vmx_setup_tsc_scaling;
-    }
 
     model_specific_lbr = get_model_specific_lbr();
     lbr_tsx_fixup_check();
--- a/xen/arch/x86/include/asm/hvm/hvm.h
+++ b/xen/arch/x86/include/asm/hvm/hvm.h
@@ -240,9 +240,6 @@ struct hvm_function_table {
         uint8_t  ratio_frac_bits;
         /* maximum-allowed TSC scaling ratio */
         uint64_t max_ratio;
-
-        /* Architecture function to setup TSC scaling ratio */
-        void (*setup)(struct vcpu *v);
     } tsc_scaling;
 };