linux-kernel - Re: [RFC/HACK] x86: Fast return to kernel

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Message-ID: <53641035.4040202@intel.com>
Date:	Fri, 02 May 2014 14:37:57 -0700
From:	"H. Peter Anvin" <h.peter.anvin@...el.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Gleb Natapov <gleb@...nel.org>,
	Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [RFC/HACK] x86: Fast return to kernel

On 05/02/2014 02:07 PM, Linus Torvalds wrote:
> On Fri, May 2, 2014 at 2:04 PM, Andy Lutomirski <luto@...capital.net> wrote:
>>
>> Because otherwise I'd have to keep track of whether it's a zeroentry
>> or an errorentry.  I can't stuff the offset in a register without even
>> more stack hackery, since there are no available registers there.  I
>> could split the whole thing into two code paths, I guess.
> 
> Ahh. Never mind. I didn't think about the fact that the error entry
> case had one more field on the stack. Your approach is all fine, it
> was me not seeing the problem.
> 

I have to admit to being rather partial to the idea of simply doing
"push $0" on entry for the vectors that don't push an error code, like
the early exception handling code does.

	-hpa


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