linux-kernel - Re: [PATCH v2] x86: Return to kernel without IRET

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Message-ID: <CALCETrVVRN3gEhhtg=r3eZK-zH0qV3qFXuiLD8guCEAiOBP__A@mail.gmail.com>
Date:	Sat, 3 May 2014 16:51:37 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>, Gleb Natapov <gleb@...nel.org>,
	Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v2] x86: Return to kernel without IRET

On Sat, May 3, 2014 at 3:19 PM, H. Peter Anvin <hpa@...or.com> wrote:
> On 05/03/2014 04:24 AM, Steven Rostedt wrote:
>> On Fri, 02 May 2014 21:03:10 -0700
>> "H. Peter Anvin" <hpa@...or.com> wrote:
>>
>>>
>>> I'd really like to see a workload which would genuinely benefit before
>>> adding more complexity.  Now... if we can determine that it doesn't harm
>>> anything and would solve the NMI nesting problem cleaner than the
>>> current solution, that would justify things, too...
>>>
>>
>> As I stated before. It doesn't solve the NMI nesting problem. It only
>> handles page faults. We would have to implement this for breakpoint
>> return paths too. Is that a plan as well?
>>
>
> I would assume we would do it for *ALL* the IRETs.  There are only three
> IRETs in the kernel last I checked...

I think we should carefully avoid doing it for returns from NMI, though :)

If you want a realistic benchmark that will speed up, packet
forwarding might be a good place to look.

--Andy
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