x86/fpu: create lazy and non-lazy FPU restore functions

Currently Xen relies on #NM (via CR0.TS) to trigger FPU context
restore. But not all FPU state is tracked by TS bit. This function
creates two FPU restore functions: vcpu_restore_fpu_lazy() and
vcpu_restore_fpu_eager(). vcpu_restore_fpu_lazy() is still used when
#NM is triggered. vcpu_restore_fpu_eager(), as a comparision, is
called for vcpu which is being scheduled in on every context
switch. To minimize restore overhead, it creates a flag,
nonlazy_xstate_used, to control non-lazy restore.

Signed-off-by: Wei Huang <wei.huang2@amd.com>

1 files changed, 20 insertions, 5 deletions

diff --git a/xen/arch/x86/i387.c b/xen/arch/x86/i387.c
index 9350f734d5..e5780ef81b 100644
--- a/xen/arch/x86/i387.c
+++ b/xen/arch/x86/i387.c
@@ -98,13 +98,13 @@ static inline void fpu_frstor(struct vcpu *v)
 /*      FPU Save Functions     */
 /*******************************/
 /* Save x87 extended state */
-static inline void fpu_xsave(struct vcpu *v, uint64_t mask)
+static inline void fpu_xsave(struct vcpu *v)
 {
     /* XCR0 normally represents what guest OS set. In case of Xen itself,
      * we set all accumulated feature mask before doing save/restore.
      */
     set_xcr0(v->arch.xcr0_accum);
-    xsave(v, mask);
+    xsave(v, v->arch.nonlazy_xstate_used ? XSTATE_ALL : XSTATE_LAZY);
     set_xcr0(v->arch.xcr0);    
 }
 
@@ -160,10 +160,25 @@ 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)
+{
+    ASSERT(!is_idle_vcpu(v));
+    
+    /* save the nonlazy extended state which is not tracked by CR0.TS bit */
+    if ( v->arch.nonlazy_xstate_used )
+    {
+        /* Avoid recursion */
+        clts();        
+        fpu_xrstor(v, XSTATE_NONLAZY);
+        stts();
+    }
+}
+
 /* 
  * Restore FPU state when #NM is triggered.
  */
-void vcpu_restore_fpu(struct vcpu *v)
+void vcpu_restore_fpu_lazy(struct vcpu *v)
 {
     ASSERT(!is_idle_vcpu(v));
 
@@ -174,7 +189,7 @@ void vcpu_restore_fpu(struct vcpu *v)
         return;
 
     if ( xsave_enabled(v) )
-        fpu_xrstor(v, XSTATE_ALL);
+        fpu_xrstor(v, XSTATE_LAZY);
     else if ( v->fpu_initialised )
     {
         if ( cpu_has_fxsr )
@@ -204,7 +219,7 @@ void vcpu_save_fpu(struct vcpu *v)
     clts();
 
     if ( xsave_enabled(v) )
-        fpu_xsave(v, XSTATE_ALL);
+        fpu_xsave(v);
     else if ( cpu_has_fxsr )
         fpu_fxsave(v);
     else