[tip:x86/fpu] x86/fpu: Remove preempt_disable() in fpu__clear()

tip-bot for Sebastian Andrzej Siewior
2019-04-13T20:48:23Z

Commit-ID: 60e528d6ce3f60a058bbb64f8acb2a07f84b172a
Gitweb: https://git.kernel.org/tip/60e528d6ce3f60a058bbb64f8acb2a07f84b172a
Author: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
AuthorDate: Wed, 3 Apr 2019 18:41:32 +0200
Committer: Borislav Petkov <bp@suse.de>
CommitDate: Tue, 9 Apr 2019 19:27:46 +0200

x86/fpu: Remove preempt_disable() in fpu__clear()

The preempt_disable() section was introduced in commit

a10b6a16cdad8 ("x86/fpu: Make the fpu state change in fpu__clear() scheduler-atomic")

and it was said to be temporary.

fpu__initialize() initializes the FPU struct to its initial value and
then sets ->initialized to 1. The last part is the important one.
The content of the state does not matter because it gets set via
copy_init_fpstate_to_fpregs().

A preemption here has little meaning because the registers will always be
set to the same content after copy_init_fpstate_to_fpregs(). A softirq
with a kernel_fpu_begin() could also force to save FPU's registers after
fpu__initialize() without changing the outcome here.

Remove the preempt_disable() section in fpu__clear(), preemption here
does not hurt.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-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: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: kvm ML <kvm@vger.kernel.org>
Cc: Nicolai Stange <nstange@suse.de>
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/20190403164156.19645-4-bigeasy@linutronix.de
---
arch/x86/kernel/fpu/core.c | 2 --
1 file changed, 2 deletions(-)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 1d3ae7988f7f..1940319268ae 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -366,11 +366,9 @@ void fpu__clear(struct fpu *fpu)
* Make sure fpstate is cleared and initialized.
*/
if (static_cpu_has(X86_FEATURE_FPU)) {
- preempt_disable();
fpu__initialize(fpu);
user_fpu_begin();
copy_init_fpstate_to_fpregs();
- preempt_enable();
}
}