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    Subject[PATCH 056/208] x86/fpu: Remove task_disable_lazy_fpu_restore()
    Date
    Replace task_disable_lazy_fpu_restore() with easier to read
    open-coded uses: we already update the fpu->last_cpu field
    explicitly in other cases.

    (This also removes yet another task_struct using FPU method.)

    Better explain the fpu::last_cpu field in the structure definition.

    Reviewed-by: Borislav Petkov <bp@alien8.de>
    Cc: Andy Lutomirski <luto@amacapital.net>
    Cc: Dave Hansen <dave.hansen@linux.intel.com>
    Cc: Fenghua Yu <fenghua.yu@intel.com>
    Cc: H. Peter Anvin <hpa@zytor.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Oleg Nesterov <oleg@redhat.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    arch/x86/include/asm/fpu-internal.h | 14 ++------------
    arch/x86/include/asm/fpu/types.h | 11 +++++++++++
    arch/x86/kernel/fpu/core.c | 5 ++---
    3 files changed, 15 insertions(+), 15 deletions(-)

    diff --git a/arch/x86/include/asm/fpu-internal.h b/arch/x86/include/asm/fpu-internal.h
    index e8f7134f0ffb..76a1f3529881 100644
    --- a/arch/x86/include/asm/fpu-internal.h
    +++ b/arch/x86/include/asm/fpu-internal.h
    @@ -74,16 +74,6 @@ static inline void __cpu_disable_lazy_restore(unsigned int cpu)
    per_cpu(fpu_fpregs_owner_ctx, cpu) = NULL;
    }

    -/*
    - * Used to indicate that the FPU state in memory is newer than the FPU
    - * state in registers, and the FPU state should be reloaded next time the
    - * task is run. Only safe on the current task, or non-running tasks.
    - */
    -static inline void task_disable_lazy_fpu_restore(struct task_struct *tsk)
    -{
    - tsk->thread.fpu.last_cpu = ~0;
    -}
    -
    static inline int fpu_lazy_restore(struct task_struct *new, unsigned int cpu)
    {
    return &new->thread.fpu == this_cpu_read_stable(fpu_fpregs_owner_ctx) &&
    @@ -430,7 +420,7 @@ static inline fpu_switch_t switch_fpu_prepare(struct task_struct *old, struct ta

    if (old_fpu->has_fpu) {
    if (!fpu_save_init(&old->thread.fpu))
    - task_disable_lazy_fpu_restore(old);
    + old->thread.fpu.last_cpu = -1;
    else
    old->thread.fpu.last_cpu = cpu;

    @@ -446,7 +436,7 @@ static inline fpu_switch_t switch_fpu_prepare(struct task_struct *old, struct ta
    stts();
    } else {
    old->thread.fpu.counter = 0;
    - task_disable_lazy_fpu_restore(old);
    + old->thread.fpu.last_cpu = -1;
    if (fpu.preload) {
    new->thread.fpu.counter++;
    if (fpu_lazy_restore(new, cpu))
    diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h
    index f6317d9aa808..cad1c37d9ea2 100644
    --- a/arch/x86/include/asm/fpu/types.h
    +++ b/arch/x86/include/asm/fpu/types.h
    @@ -125,7 +125,18 @@ union thread_xstate {
    };

    struct fpu {
    + /*
    + * Records the last CPU on which this context was loaded into
    + * FPU registers. (In the lazy-switching case we might be
    + * able to reuse FPU registers across multiple context switches
    + * this way, if no intermediate task used the FPU.)
    + *
    + * A value of -1 is used to indicate that the FPU state in context
    + * memory is newer than the FPU state in registers, and that the
    + * FPU state should be reloaded next time the task is run.
    + */
    unsigned int last_cpu;
    +
    unsigned int has_fpu;
    union thread_xstate *state;
    /*
    diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
    index 39b78f1cc93b..59378e36b2ce 100644
    --- a/arch/x86/kernel/fpu/core.c
    +++ b/arch/x86/kernel/fpu/core.c
    @@ -242,8 +242,7 @@ int fpu__copy(struct task_struct *dst, struct task_struct *src)
    dst->thread.fpu.counter = 0;
    dst->thread.fpu.has_fpu = 0;
    dst->thread.fpu.state = NULL;
    -
    - task_disable_lazy_fpu_restore(dst);
    + dst->thread.fpu.last_cpu = -1;

    if (src_fpu->fpstate_active) {
    int err = fpstate_alloc(dst_fpu);
    @@ -319,7 +318,7 @@ static int fpu__unlazy_stopped(struct task_struct *child)
    return -EINVAL;

    if (child_fpu->fpstate_active) {
    - task_disable_lazy_fpu_restore(child);
    + child->thread.fpu.last_cpu = -1;
    return 0;
    }

    --
    2.1.0


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