[Xen-devel] [PATCH] x86/EFI: further correct FPU state handling around runtime calls

["Jan Beulich" <JBeulich@xxxxxxxx>]

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.

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

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -1636,7 +1636,7 @@ static void __context_switch(void)
             if ( cpu_has_xsaves && is_hvm_vcpu(n) )
                 set_msr_xss(n->arch.hvm_vcpu.msr_xss);
         }
-        vcpu_restore_fpu_eager(n);
+        vcpu_restore_fpu_eager(n, false);
         nd->arch.ctxt_switch->to(n);
     }
 
--- a/xen/arch/x86/hvm/emulate.c
+++ b/xen/arch/x86/hvm/emulate.c
@@ -2146,7 +2146,7 @@ static void hvmemul_put_fpu(
          *   by hvmemul_get_fpu().
          */
         if ( curr->arch.fully_eager_fpu )
-            vcpu_restore_fpu_eager(curr);
+            vcpu_restore_fpu_eager(curr, false);
         else
         {
             curr->fpu_dirtied = false;
--- a/xen/arch/x86/i387.c
+++ b/xen/arch/x86/i387.c
@@ -206,11 +206,11 @@ static inline void fpu_fxsave(struct vcp
 /*       VCPU FPU Functions    */
 /*******************************/
 /* Restore FPU state whenever VCPU is schduled in. */
-void vcpu_restore_fpu_eager(struct vcpu *v)
+void vcpu_restore_fpu_eager(struct vcpu *v, bool need_stts)
 {
     /* Restore nonlazy extended state (i.e. parts not tracked by CR0.TS). */
     if ( !v->arch.fully_eager_fpu && !v->arch.nonlazy_xstate_used )
-        return;
+        goto maybe_stts;
 
     ASSERT(!is_idle_vcpu(v));
 
@@ -233,14 +233,17 @@ void vcpu_restore_fpu_eager(struct vcpu
         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);
     }
     else
     {
         fpu_xrstor(v, XSTATE_NONLAZY);
-        stts();
+        need_stts = true;
     }
+
+ maybe_stts:
+    if ( need_stts )
+        stts();
 }
 
 /* 
--- a/xen/common/efi/runtime.c
+++ b/xen/common/efi/runtime.c
@@ -135,7 +135,7 @@ void efi_rs_leave(struct efi_rs_state *s
     irq_exit();
     efi_rs_on_cpu = NR_CPUS;
     spin_unlock(&efi_rs_lock);
-    vcpu_restore_fpu_eager(curr);
+    vcpu_restore_fpu_eager(curr, true);
 }
 
 bool efi_rs_using_pgtables(void)
--- a/xen/include/asm-x86/i387.h
+++ b/xen/include/asm-x86/i387.h
@@ -28,7 +28,7 @@ struct ix87_env {
     uint16_t fds, _res6;
 };
 
-void vcpu_restore_fpu_eager(struct vcpu *v);
+void vcpu_restore_fpu_eager(struct vcpu *v, bool need_stts);
 void vcpu_restore_fpu_lazy(struct vcpu *v);
 void vcpu_save_fpu(struct vcpu *v);
 void save_fpu_enable(void);





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