linux-kernel - Re: [tip:x86/efi] x86/efi: Check for unsafe dealing with FPU state in irq ctxt

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Message-ID: <53909E46.4020904@zytor.com>
Date:	Thu, 05 Jun 2014 09:43:50 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Borislav Petkov <bp@...en8.de>
CC:	Andy Lutomirski <luto@...capital.net>,
	Matt Fleming <matt.fleming@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"linux-tip-commits@...r.kernel.org" 
	<linux-tip-commits@...r.kernel.org>
Subject: Re: [tip:x86/efi] x86/efi: Check for unsafe dealing with FPU state
 in irq ctxt

On 06/05/2014 09:37 AM, Borislav Petkov wrote:
> On Thu, Jun 05, 2014 at 09:31:12AM -0700, H. Peter Anvin wrote:
>> The bottom line is that we can't call EFI from a context where we can't
>> use the FPU.  Or specifically, we can't then resume execution.
> 
> Can't we allocate a save-state area, stash the state there and let EFI
> scribble over it? When EFI returns, we scribble over it back assuming it
> has done the saving/restoring on its own.

I'm sorry I don't follow.

	-hpa

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