Re: [PATCH 2/4] x86/fpu: introduce restore_init_xstate()

From: Borislav Petkov
Date: Fri Mar 13 2015 - 06:35:43 EST

On Wed, Mar 11, 2015 at 06:34:29PM +0100, Oleg Nesterov wrote:
> Extract the "use_eager_fpu()" code from drop_init_fpu() into the new
> simple helper, restore_init_xstate(). The next patch adds another user.
> - It is not clear why we do not check use_fxsr() like fpu_restore_checking()
> does.

Tell me about it.

> - It is not clear why we can't call setup_init_fpu_buf() unconditionally
> to always create init_xstate_buf().

I also don't understand what the thought behind xstate_enable_boot_cpu()
and eager_fpu_init_bp() - we do call xstate_enable_boot_cpu() and alloc
init_xstate_buf and then when we come to

|-> eager_fpu_init_bp

we get to init it if not initted yet.

When can that ever happen?

> Then do_device_not_available() path
> (at least) could use restore_init_xstate() too. It doesn't need to init
> fpu->state, its content doesn't matter until unlazy_fpu/__switch_to/etc
> which overwrites this memory anyway.
> Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
> ---
> arch/x86/include/asm/fpu-internal.h | 16 ++++++++++------
> 1 files changed, 10 insertions(+), 6 deletions(-)

Applied, thanks.


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