linux-kernel - Re: [PATCH 15/22] x86/entry: Add TIF_NEED_FPU

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Date:   Wed, 13 Feb 2019 10:35:53 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Andy Lutomirski <luto@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        kvm@...r.kernel.org, "Jason A. Donenfeld" <Jason@...c4.com>,
        Rik van Riel <riel@...riel.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH 15/22] x86/entry: Add TIF_NEED_FPU_LOAD

On Thu, Feb 07, 2019 at 12:49:42PM +0100, Sebastian Andrzej Siewior wrote:
> On 2019-01-30 12:55:07 [+0100], Borislav Petkov wrote:
> > This definitely needs to be written somewhere in
> > 
> > arch/x86/include/asm/fpu/internal.h
> > 
> > or where we decide to put the FPU handling rules.
> 
> Added:
> 
> Index: staging/arch/x86/include/asm/fpu/internal.h
> ===================================================================
> --- staging.orig/arch/x86/include/asm/fpu/internal.h
> +++ staging/arch/x86/include/asm/fpu/internal.h
> @@ -537,6 +537,12 @@ static inline void __fpregs_load_activat
>   *
>   * The FPU context is only stored/restore for user task and ->mm is used to
>   * distinguish between kernel and user threads.
> + *
> + * If TIF_NEED_FPU_LOAD is cleared then CPU's FPU registers are holding the
> + * current content of current()'s FPU register state.

"current content of current" - that's a lot of c...

Make that

"... then the CPU's FPU registers are mirrored in the current thread's
FPU registers state."

> + * If TIF_NEED_FPU_LOAD is set then CPU's FPU registers may not hold current()'s
> + * FPU registers. It is required to load the register before returning to
						^^^^^^^^

s/register/registers/ - plural.

Thx.

-- 
Regards/Gruss,
    Boris.

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