[PATCH v1 8/8] x86: Cleanup cr0.TS flag handling

[Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>]

With lazy FPU removed, Xen does not need to touch the cr0.TS flag on context
switch except when saving/restoring the FPU for a PV guest.

Signed-off-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
---
 xen/arch/x86/cpu/common.c       |  3 ---
 xen/arch/x86/hvm/emulate.c      | 14 ++------------
 xen/arch/x86/i387.c             | 22 +++-------------------
 xen/arch/x86/include/asm/i387.h |  1 -
 xen/common/efi/runtime.c        |  2 +-
 5 files changed, 6 insertions(+), 36 deletions(-)

diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c
index 5d0523a78b52..04a049f01c07 100644
--- a/xen/arch/x86/cpu/common.c
+++ b/xen/arch/x86/cpu/common.c
@@ -883,9 +883,6 @@ void cpu_init(void)
        /* Install correct page table. */
        write_ptbase(current);
 
-       /* Ensure FPU gets initialised for each domain. */
-       stts();
-
        /* Reset debug registers: */
        write_debugreg(0, 0);
        write_debugreg(1, 0);
diff --git a/xen/arch/x86/hvm/emulate.c b/xen/arch/x86/hvm/emulate.c
index 48c7320360c7..f3aae158e9f8 100644
--- a/xen/arch/x86/hvm/emulate.c
+++ b/xen/arch/x86/hvm/emulate.c
@@ -2527,14 +2527,8 @@ static int cf_check hvmemul_get_fpu(
          * Latch current register state so that we can back out changes
          * if needed (namely when a memory write fails after register state
          * has already been updated).
-         * NB: We don't really need the "enable" part of the called function
-         * (->fpu_dirtied set implies CR0.TS clear), but the additional
-         * overhead should be low enough to not warrant introduction of yet
-         * another slightly different function. However, we need to undo the
-         * ->fpu_dirtied clearing the function does as well as the possible
-         * masking of all exceptions by FNSTENV.)
          */
-        save_fpu_enable();
+        vcpu_save_fpu(curr);
         if ( (fpu_ctxt->fcw & 0x3f) != 0x3f )
         {
             uint16_t fcw;
@@ -2572,12 +2566,8 @@ static void cf_check hvmemul_put_fpu(
          * Latch current register state so that we can replace FIP/FDP/FOP
          * (which have values resulting from our own invocation of the FPU
          * instruction during emulation).
-         * NB: See also the comment in hvmemul_get_fpu(); we don't need to
-         * set ->fpu_dirtied here as it is going to be cleared below, and
-         * we also don't need to reload FCW as we're forcing full state to
-         * be reloaded anyway.
          */
-        save_fpu_enable();
+        vcpu_save_fpu(curr);
 
         if ( boot_cpu_has(X86_FEATURE_FDP_EXCP_ONLY) &&
              !(fpu_ctxt->fsw & ~fpu_ctxt->fcw & 0x003f) )
diff --git a/xen/arch/x86/i387.c b/xen/arch/x86/i387.c
index 9acaaf4673df..336bc83b6e13 100644
--- a/xen/arch/x86/i387.c
+++ b/xen/arch/x86/i387.c
@@ -176,9 +176,6 @@ void vcpu_restore_fpu(struct vcpu *v)
 {
     ASSERT(!is_idle_vcpu(v));
 
-    /* Avoid recursion */
-    clts();
-
     if ( cpu_has_xsave )
         fpu_xrstor(v, XSTATE_ALL);
     else
@@ -193,31 +190,18 @@ void vcpu_restore_fpu(struct vcpu *v)
  * On each context switch, save the necessary FPU info of VCPU being switch 
  * out. It dispatches saving operation based on CPU's capability.
  */
-static bool _vcpu_save_fpu(struct vcpu *v)
+void vcpu_save_fpu(struct vcpu *v)
 {
     ASSERT(!is_idle_vcpu(v));
 
     /* This can happen, if a paravirtualised guest OS has set its CR0.TS. */
-    clts();
+    if ( is_pv_vcpu(v) )
+        clts();
 
     if ( cpu_has_xsave )
         fpu_xsave(v);
     else
         fpu_fxsave(v);
-
-    return true;
-}
-
-void vcpu_save_fpu(struct vcpu *v)
-{
-    _vcpu_save_fpu(v);
-    stts();
-}
-
-void save_fpu_enable(void)
-{
-    if ( !_vcpu_save_fpu(current) )
-        clts();
 }
 
 /* Initialize FPU's context save area */
diff --git a/xen/arch/x86/include/asm/i387.h b/xen/arch/x86/include/asm/i387.h
index fe5e4419b6f4..0717005d31f0 100644
--- a/xen/arch/x86/include/asm/i387.h
+++ b/xen/arch/x86/include/asm/i387.h
@@ -29,7 +29,6 @@ struct ix87_env {
 
 void vcpu_restore_fpu(struct vcpu *v);
 void vcpu_save_fpu(struct vcpu *v);
-void save_fpu_enable(void);
 int vcpu_init_fpu(struct vcpu *v);
 void vcpu_destroy_fpu(struct vcpu *v);
 
diff --git a/xen/common/efi/runtime.c b/xen/common/efi/runtime.c
index 982e42e8f341..0f1cc765ec5e 100644
--- a/xen/common/efi/runtime.c
+++ b/xen/common/efi/runtime.c
@@ -94,7 +94,7 @@ struct efi_rs_state efi_rs_enter(void)
         return state;
 
     state.cr3 = read_cr3();
-    save_fpu_enable();
+    vcpu_save_fpu(current);
     asm volatile ( "fnclex; fldcw %0" :: "m" (fcw) );
     asm volatile ( "ldmxcsr %0" :: "m" (mxcsr) );
 
-- 
2.53.0