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@suse.com>

diff --git a/xen/arch/x86/efi/runtime.c b/xen/arch/x86/efi/runtime.c
index d7c884b1ca0d694044676273afe7b73cc655f169..166852decc86688f076c5517304a3e8333b85213 100644 (file)
--- 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;
@@ -45,8 +47,14 @@ const struct efi_pci_rom *__read_mostly efi_pci_roms;
 
 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 */
@@ -82,6 +90,7 @@ 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 bd72138878200c83ea1aeb27e7b52b98db537dd7..a372e0b503ba2ae51fe8111580f9f8ea71e88080 100644 (file)
--- a/xen/arch/x86/i387.c
+++ b/xen/arch/x86/i387.c
@@ -266,10 +266,10 @@ 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));
 
@@ -284,9 +284,22 @@ 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 38dbcae1a9521404080c9e3c862f9065961c1ade..150a09e41f150ccf5509dd972af967122515e06f 100644 (file)
--- 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);