x86/EFI: further correct FPU state handling around runtime calls

We must not leave a vCPU with CR0.TS clear when it is not in fully eager
mode and has not touched non-lazy state. Instead of adding a 3rd
invocation of stts() to vcpu_restore_fpu_eager(), consolidate all of
them into a single one done at the end of the function.

Rename the function at the same time to better reflect its purpose, as
the patches touches all of its occurences anyway.

The new function parameter is not really well named, but
"need_stts_if_not_fully_eager" seemed excessive to me.

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

xen/arch/x86/domain.c

@@ -1703,7 +1703,7 @@ static void __context_switch(void)
             if ( xcr0 != get_xcr0() && !set_xcr0(xcr0) )
                 BUG();
         }
-        vcpu_restore_fpu_eager(n);
+        vcpu_restore_fpu_nonlazy(n, 0);
         n->arch.ctxt_switch_to(n);
     }
 

xen/arch/x86/i387.c

@@ -212,7 +212,7 @@ static inline void fpu_fsave(struct vcpu *v)
 /*       VCPU FPU Functions    */
 /*******************************/
 /* Restore FPU state whenever VCPU is schduled in. */
-void vcpu_restore_fpu_eager(struct vcpu *v)
+void vcpu_restore_fpu_nonlazy(struct vcpu *v, bool_t need_stts)
 {
     if ( v->arch.fully_eager_fpu )
     {
@@ -230,8 +230,7 @@ void vcpu_restore_fpu_eager(struct vcpu *v)
         v->fpu_dirtied = 1;
 
         /* Xen doesn't need TS set, but the guest might. */
-        if ( is_pv_vcpu(v) && (v->arch.pv_vcpu.ctrlreg[0] & X86_CR0_TS) )
-            stts();
+        need_stts = is_pv_vcpu(v) && (v->arch.pv_vcpu.ctrlreg[0] & X86_CR0_TS);
     }
     /* save the nonlazy extended state which is not tracked by CR0.TS bit */
     else if ( v->arch.nonlazy_xstate_used )
@@ -241,8 +240,11 @@ void vcpu_restore_fpu_eager(struct vcpu *v)
         /* Avoid recursion */
         clts();        
         fpu_xrstor(v, XSTATE_NONLAZY);
-        stts();
+        need_stts = 1;
     }
+
+    if ( need_stts )
+        stts();
 }
 
 /* 

xen/common/efi/runtime.c

@@ -128,7 +128,7 @@ void efi_rs_leave(struct efi_rs_state *state)
     irq_exit();
     efi_rs_on_cpu = NR_CPUS;
     spin_unlock(&efi_rs_lock);
-    vcpu_restore_fpu_eager(curr);
+    vcpu_restore_fpu_nonlazy(curr, 1);
 }
 
 bool_t efi_rs_using_pgtables(void)

xen/include/asm-x86/i387.h

@@ -35,7 +35,7 @@ struct ix87_state {
     } r[8];
 };
 
-void vcpu_restore_fpu_eager(struct vcpu *v);
+void vcpu_restore_fpu_nonlazy(struct vcpu *v, bool_t need_stts);
 void vcpu_restore_fpu_lazy(struct vcpu *v);
 void vcpu_save_fpu(struct vcpu *v);
 void save_fpu_enable(void);