x86/fpu: Prepare copy_fpstate_to_sigframe() for TIF_NEED_FPU_LOAD

The FPU registers need only to be saved if TIF_NEED_FPU_LOAD is not set.
Otherwise this has been already done and can be skipped.

 [ bp: Massage a bit. ]

Signed-off-by: Rik van Riel <riel@surriel.com>
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/20190403164156.19645-19-bigeasy@linutronix.de

diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index 8f23f523721852436061960f5e7f0e0cce4f01fb..9b9dfdc962856019913e3f9f9e2e11e6a6af112d 100644 (file)
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -171,7 +171,17 @@ int copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size)
                        sizeof(struct user_i387_ia32_struct), NULL,
                        (struct _fpstate_32 __user *) buf) ? -1 : 1;
 
-       copy_fpregs_to_fpstate(fpu);
+       /*
+        * If we do not need to load the FPU registers at return to userspace
+        * then the CPU has the current state and we need to save it. Otherwise,
+        * it has already been done and we can skip it.
+        */
+       fpregs_lock();
+       if (!test_thread_flag(TIF_NEED_FPU_LOAD)) {
+               copy_fpregs_to_fpstate(fpu);
+               set_thread_flag(TIF_NEED_FPU_LOAD);
+       }
+       fpregs_unlock();
 
        if (using_compacted_format()) {
                if (copy_xstate_to_user(buf_fx, xsave, 0, size))