x86/fpu: Provide a proper function for ex_handler_fprestore()

To make upcoming changes for support of dynamically enabled features
simpler, provide a proper function for the exception handler which removes
exposure of FPU internals.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211015011540.053515012@linutronix.de

arch/x86/include/asm/fpu/api.h

@@ -113,6 +113,7 @@ static inline void update_pasid(void) { }
 /* Trap handling */
 extern int  fpu__exception_code(struct fpu *fpu, int trap_nr);
 extern void fpu_sync_fpstate(struct fpu *fpu);
+extern void fpu_reset_from_exception_fixup(void);
 
 /* Boot, hotplug and resume */
 extern void fpu__init_cpu(void);
@@ -129,9 +130,6 @@ static inline void fpstate_init_soft(struct swregs_state *soft) {}
 /* State tracking */
 DECLARE_PER_CPU(struct fpu *, fpu_fpregs_owner_ctx);
 
-/* fpstate */
-extern union fpregs_state init_fpstate;
-
 /* fpstate-related functions which are exported to KVM */
 extern void fpu_init_fpstate_user(struct fpu *fpu);
 

arch/x86/kernel/fpu/core.c

@@ -155,6 +155,11 @@ void restore_fpregs_from_fpstate(union fpregs_state *fpstate, u64 mask)
 	}
 }
 
+void fpu_reset_from_exception_fixup(void)
+{
+	restore_fpregs_from_fpstate(&init_fpstate, xfeatures_mask_fpstate());
+}
+
 #if IS_ENABLED(CONFIG_KVM)
 void fpu_swap_kvm_fpu(struct fpu *save, struct fpu *rstor, u64 restore_mask)
 {

arch/x86/kernel/fpu/internal.h

@@ -2,6 +2,8 @@
 #ifndef __X86_KERNEL_FPU_INTERNAL_H
 #define __X86_KERNEL_FPU_INTERNAL_H
 
+extern union fpregs_state init_fpstate;
+
 /* CPU feature check wrappers */
 static __always_inline __pure bool use_xsave(void)
 {

arch/x86/mm/extable.c

@@ -4,8 +4,7 @@
 #include <linux/sched/debug.h>
 #include <xen/xen.h>
 
-#include <asm/fpu/signal.h>
-#include <asm/fpu/xstate.h>
+#include <asm/fpu/api.h>
 #include <asm/sev.h>
 #include <asm/traps.h>
 #include <asm/kdebug.h>
@@ -48,7 +47,7 @@ static bool ex_handler_fprestore(const struct exception_table_entry *fixup,
 	WARN_ONCE(1, "Bad FPU state detected at %pB, reinitializing FPU registers.",
 		  (void *)instruction_pointer(regs));
 
-	restore_fpregs_from_fpstate(&init_fpstate, xfeatures_mask_fpstate());
+	fpu_reset_from_exception_fixup();
 	return true;
 }