x86/fpu: Inline copy_user_to_fpregs_zeroing()

Start refactoring __fpu__restore_sig() by inlining
copy_user_to_fpregs_zeroing(). The original function remains and will be
used to restore from userland memory if possible.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Dave Hansen <dave.hansen@intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: kvm ML <kvm@vger.kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/20190403164156.19645-21-bigeasy@linutronix.de

arch/x86/kernel/fpu/signal.c

@@ -337,11 +337,29 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
 		kfree(tmp);
 		return err;
 	} else {
+		int ret;
+
 		/*
 		 * For 64-bit frames and 32-bit fsave frames, restore the user
 		 * state to the registers directly (with exceptions handled).
 		 */
-		if (copy_user_to_fpregs_zeroing(buf_fx, xfeatures, fx_only)) {
+		if (use_xsave()) {
+			if ((unsigned long)buf_fx % 64 || fx_only) {
+				u64 init_bv = xfeatures_mask & ~XFEATURE_MASK_FPSSE;
+				copy_kernel_to_xregs(&init_fpstate.xsave, init_bv);
+				ret = copy_user_to_fxregs(buf_fx);
+			} else {
+				u64 init_bv = xfeatures_mask & ~xfeatures;
+				if (unlikely(init_bv))
+					copy_kernel_to_xregs(&init_fpstate.xsave, init_bv);
+				ret = copy_user_to_xregs(buf_fx, xfeatures);
+			}
+		} else if (use_fxsr()) {
+			ret = copy_user_to_fxregs(buf_fx);
+		} else
+			ret = copy_user_to_fregs(buf_fx);
+
+		if (ret) {
 			fpu__clear(fpu);
 			return -1;
 		}