Re: [patch V3 51/66] x86/fpu: Dont restore PKRU in fpregs_restore_userspace()

[Borislav Petkov]

On Fri, Jun 18, 2021 at 04:19:14PM +0200, Thomas Gleixner wrote:
> switch_to(), flush_thread() write the task's PKRU value eagerly so the PKRU
> value of current is always valid in the hardware.
> 
> That means there is no point in restoring PKRU on exit to user or when
> reactivating the task's FPU registers in the signal frame setup path.
> 
> This allows to remove all the xstate buffer updates with PKRU values once
> the PKRU state is stored in thread struct while a task is scheduled out.
> 
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> ---
> V3: Restore supervisor state too. (Yu-Cheng)
> ---
>  arch/x86/include/asm/fpu/internal.h |   16 +++++++++++++++-
>  arch/x86/include/asm/fpu/xstate.h   |   19 +++++++++++++++++++
>  arch/x86/kernel/fpu/core.c          |    2 +-
>  3 files changed, 35 insertions(+), 2 deletions(-)

Reviewed-by: Borislav Petkov <bp@xxxxxxx>

-- 
Regards/Gruss,
    Boris.

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