linux-kernel - Re: [RFC][PATCH 1/2] x86, fpu: wrap get_xsave

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Message-ID: <20150130183819.GA20732@redhat.com>
Date:	Fri, 30 Jan 2015 19:38:19 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Dave Hansen <dave@...1.net>
Cc:	dave.hansen@...ux.intel.com, riel@...hat.com, sbsiddha@...il.com,
	luto@...capital.net, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, fenghua.yu@...el.com, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 1/2] x86, fpu: wrap get_xsave_addr() to make it
	safer

On 01/30, Oleg Nesterov wrote:
>
> On 01/30, Dave Hansen wrote:
> >
> > +void *tsk_get_xsave_field(struct task_struct *tsk, int xsave_field)
> > +{
> > +	union thread_xstate *xstate;
> > +
> > +	unlazy_fpu(tsk);
> 
> ack, but to remind this depends on 2/3 I sent.
> 
> > +	xstate = tsk->thread.fpu.state;
> > +	/*
> > +	 * This might be unallocated if the FPU
> > +	 * was never in use.
> > +	 */
> > +	if (!xstate)
> > +		return NULL;
> 
> This is cosmetic, unlazy_fpu() is safe if !xstate, __thread_has_fpu()
> is not possible in this case.
> 
> But perhaps
> 
> 	if (!used_math())
> 		return NULL;
> 
> will look better.

at the start of this helper, I meant

Oleg.

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