[Xen-changelog] [xen stable-4.2] x86/EFI: allow FPU/XMM use in runtime service functions

[patchbot@xxxxxxx]

commit da777ed3296ef58f23805cfeefde6427a7d2365a
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Tue Jun 24 10:24:20 2014 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Jun 24 10:24:20 2014 +0200

    x86/EFI: allow FPU/XMM use in runtime service functions
    
    UEFI spec update 2.4B developed a requirement to enter runtime service
    functions with CR0.TS (and CR0.EM) clear, thus making feasible the
    already previously stated permission for these functions to use some of
    the XMM registers. Enforce this requirement (along with the connected
    ones on FPU control word and MXCSR) by going through a full FPU save
    cycle (if the FPU was dirty) in efi_rs_enter() (along with loading  the
    specified values into the other two registers).
    
    Note that the UEFI spec mandates that extension registers other than
    XMM ones (for our purposes all that get restored eagerly) are preserved
    across runtime function calls, hence there's nothing we need to restore
    in efi_rs_leave() (they do get saved, but just for simplicity's sake).
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: e0fe297dabc96d8161d568f19a99722c4739b9f9
    master date: 2014-06-18 15:53:27 +0200
---
 xen/arch/x86/efi/runtime.c |    9 +++++++++
 xen/arch/x86/i387.c        |   17 +++++++++++++++--
 xen/include/asm-x86/i387.h |    1 +
 3 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/efi/runtime.c b/xen/arch/x86/efi/runtime.c
index b8847dd..fb48430 100644
--- a/xen/arch/x86/efi/runtime.c
+++ b/xen/arch/x86/efi/runtime.c
@@ -10,6 +10,8 @@ DEFINE_XEN_GUEST_HANDLE(CHAR16);
 
 #ifndef COMPAT
 
+# include <asm/i387.h>
+# include <asm/xstate.h>
 # include <public/platform.h>
 
 const bool_t efi_enabled = 1;
@@ -39,8 +41,14 @@ l4_pgentry_t *__read_mostly efi_l4_pgtable;
 
 unsigned long efi_rs_enter(void)
 {
+    static const u16 fcw = FCW_DEFAULT;
+    static const u32 mxcsr = MXCSR_DEFAULT;
     unsigned long cr3 = read_cr3();
 
+    save_fpu_enable();
+    asm volatile ( "fldcw %0" :: "m" (fcw) );
+    asm volatile ( "ldmxcsr %0" :: "m" (mxcsr) );
+
     spin_lock(&efi_rs_lock);
 
     /* prevent fixup_page_fault() from doing anything */
@@ -76,6 +84,7 @@ void efi_rs_leave(unsigned long cr3)
     }
     irq_exit();
     spin_unlock(&efi_rs_lock);
+    stts();
 }
 
 unsigned long efi_get_time(void)
diff --git a/xen/arch/x86/i387.c b/xen/arch/x86/i387.c
index 0a001fd..946a83c 100644
--- a/xen/arch/x86/i387.c
+++ b/xen/arch/x86/i387.c
@@ -276,10 +276,10 @@ void vcpu_restore_fpu_lazy(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.
  */
-void vcpu_save_fpu(struct vcpu *v)
+static bool_t _vcpu_save_fpu(struct vcpu *v)
 {
     if ( !v->fpu_dirtied && !v->arch.nonlazy_xstate_used )
-        return;
+        return 0;
 
     ASSERT(!is_idle_vcpu(v));
 
@@ -294,9 +294,22 @@ void vcpu_save_fpu(struct vcpu *v)
         fpu_fsave(v);
 
     v->fpu_dirtied = 0;
+
+    return 1;
+}
+
+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 */
 int vcpu_init_fpu(struct vcpu *v)
 {
diff --git a/xen/include/asm-x86/i387.h b/xen/include/asm-x86/i387.h
index 1f5fe50..fd268a9 100644
--- a/xen/include/asm-x86/i387.h
+++ b/xen/include/asm-x86/i387.h
@@ -38,6 +38,7 @@ struct ix87_state {
 void vcpu_restore_fpu_eager(struct vcpu *v);
 void vcpu_restore_fpu_lazy(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);
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.2

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