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Subject[tip:x86/fpu] x86/fpu: Prepare copy_fpstate_to_sigframe() for TIF_NEED_FPU_LOAD
Commit-ID:  a352a3b7b7920212ee4c45a41500c66826318e92
Gitweb: https://git.kernel.org/tip/a352a3b7b7920212ee4c45a41500c66826318e92
Author: Rik van Riel <riel@surriel.com>
AuthorDate: Wed, 3 Apr 2019 18:41:47 +0200
Committer: Borislav Petkov <bp@suse.de>
CommitDate: Thu, 11 Apr 2019 18:20:04 +0200

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
---
arch/x86/kernel/fpu/signal.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index 8f23f5237218..9b9dfdc96285 100644
--- 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))
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