linux-kernel - Re: [PATCH 23/27] x86/fpu: Defer FPU state load until return to userspace

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Message-ID: <20190412152437.d2bswajqtx7hrpkb@linutronix.de>
Date:   Fri, 12 Apr 2019 17:24:37 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Borislav Petkov <bp@...en8.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 23/27] x86/fpu: Defer FPU state load until return to
 userspace

On 2019-04-12 16:36:15 [+0200], Borislav Petkov wrote:
> On Wed, Apr 03, 2019 at 06:41:52PM +0200, Sebastian Andrzej Siewior wrote:
> > @@ -226,10 +236,9 @@ static void fpu__initialize(struct fpu *fpu)
> >  {
> >  	WARN_ON_FPU(fpu != &current->thread.fpu);
> >  
> > +	set_thread_flag(TIF_NEED_FPU_LOAD);
> >  	fpstate_init(&fpu->state);
> >  	trace_x86_fpu_init_state(fpu);
> > -
> > -	trace_x86_fpu_activate_state(fpu);
> 
> That is called nowhere after this patch.

Isn't it called from fpu__clear()?

> Shouldn't it be called below, before fpregs_activate() because
> fpregs_activate() does trace_x86_fpu_regs_activated()?

Why? fpu__initialize() wipes the FPU state and starts from zero.
fpregs_mark_activate() on the other hand marks this FPU context is
currently active.

Sebastian