linux-kernel - Re: [PATCH 0/3]: x86, fpu: unlazy

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Message-ID: <54CAC190.30905@linux.intel.com>
Date:	Thu, 29 Jan 2015 15:26:08 -0800
From:	Dave Hansen <dave.hansen@...ux.intel.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	Rik van Riel <riel@...hat.com>, Suresh Siddha <sbsiddha@...il.com>,
	Andy Lutomirski <luto@...capital.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Fenghua Yu <fenghua.yu@...el.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/3]: x86, fpu: unlazy_fpu fixes/cleanups

On 01/29/2015 01:56 PM, Oleg Nesterov wrote:
> --- x/arch/x86/kernel/traps.c
> +++ x/arch/x86/kernel/traps.c
> @@ -313,7 +313,7 @@ dotraplinkage void do_bounds(struct pt_r
>  	 * It is not directly accessible, though, so we need to
>  	 * do an xsave and then pull it out of the xsave buffer.
>  	 */
> -	fpu_save_init(&tsk->thread.fpu);
> +	unlazy_fpu(tsk);
>  	xsave_buf = &(tsk->thread.fpu.state->xsave);
...
> 	bndcsr = get_xsave_addr(xsave_buf, XSTATE_BNDCSR);

Hmm, if the the thread was not using the FPU, and this fails to save
anything in to the xsave_buf, what will bndcsr point to?  It _looks_ to
me like it will just point to uninitialized data since the xsave never
happened.

Fenghua, shouldn't get_xsave_addr() be checking the xstate bit against
the xsave->xstate_bv?
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