lkml.org 
[lkml]   [2016]   [Jan]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH 2/5] x86/fpu: Fix FNSAVE usage in eagerfpu mode
    Date
    In eager fpu mode, having deactivated fpu without immediately
    reloading some other context is illegal. Therefore, to recover from
    FNSAVE, we can't just deactivate the state -- we need to reload it
    if we're not actively context switching.

    We had this wrong in fpu__save and fpu__copy. Fix both.
    __kernel_fpu_begin was fine -- add a comment.

    This fixes a warning triggerable with nofxsr eagerfpu=on.

    Signed-off-by: Andy Lutomirski <luto@kernel.org>
    ---
    arch/x86/kernel/fpu/core.c | 18 +++++++++++++++---
    1 file changed, 15 insertions(+), 3 deletions(-)

    diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
    index 08e1e11a05ca..7a9244df33e2 100644
    --- a/arch/x86/kernel/fpu/core.c
    +++ b/arch/x86/kernel/fpu/core.c
    @@ -114,6 +114,10 @@ void __kernel_fpu_begin(void)
    kernel_fpu_disable();

    if (fpu->fpregs_active) {
    + /*
    + * Ignore return value -- we don't care if reg state
    + * is clobbered.
    + */
    copy_fpregs_to_fpstate(fpu);
    } else {
    this_cpu_write(fpu_fpregs_owner_ctx, NULL);
    @@ -189,8 +193,12 @@ void fpu__save(struct fpu *fpu)

    preempt_disable();
    if (fpu->fpregs_active) {
    - if (!copy_fpregs_to_fpstate(fpu))
    - fpregs_deactivate(fpu);
    + if (!copy_fpregs_to_fpstate(fpu)) {
    + if (use_eager_fpu())
    + copy_kernel_to_fpregs(&fpu->state);
    + else
    + fpregs_deactivate(fpu);
    + }
    }
    preempt_enable();
    }
    @@ -259,7 +267,11 @@ static void fpu_copy(struct fpu *dst_fpu, struct fpu *src_fpu)
    preempt_disable();
    if (!copy_fpregs_to_fpstate(dst_fpu)) {
    memcpy(&src_fpu->state, &dst_fpu->state, xstate_size);
    - fpregs_deactivate(src_fpu);
    +
    + if (use_eager_fpu())
    + copy_kernel_to_fpregs(&src_fpu->state);
    + else
    + fpregs_deactivate(src_fpu);
    }
    preempt_enable();
    }
    --
    2.5.0
    \
     
     \ /
      Last update: 2016-01-23 02:41    [W:3.116 / U:0.072 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site