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

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