linux-kernel - Re: [Lguest] [PATCH RFC/RFB] x86_64, i386: interrupt dispatch changes

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Message-ID: <20081127105635.GG6703@one.firstfloor.org>
Date:	Thu, 27 Nov 2008 11:56:35 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Avi Kivity <avi@...hat.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Alexander van Heukelum <heukelum@...tmail.fm>,
	lguest@...abs.org, jeremy@...source.com,
	LKML <linux-kernel@...r.kernel.org>,
	Mike Travis <travis@....com>,
	Cyrill Gorcunov <gorcunov@...il.com>,
	Steven Rostedt <srostedt@...hat.com>,
	Andi Kleen <andi@...stfloor.org>, Ingo Molnar <mingo@...e.hu>,
	Alexander van Heukelum <heukelum@...lshack.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [Lguest] [PATCH RFC/RFB] x86_64,	i386: interrupt dispatch changes

On Thu, Nov 27, 2008 at 12:13:43PM +0200, Avi Kivity wrote:
> H. Peter Anvin wrote:
> >
> >>I suspect we could get it down to three bytes, by sharing the last 
> >>byte of the four-byte call sequence with the first byte of the next:
> >>
> >> 66 e8 ff 66 e8 fc 66 e8 f9 66 e8 f6 ...
> >>
> >>Every three bytes a new stub begins; it's a four-byte call to offset 
> >>0x6703 relative to the beginning of the first stub.
> >>
> >>Can anyone better 24 bits/stub?
> >
> >On the entirely silly level...
> >
> >CC xx
> 
> Nice.  Can actually go to zero, by pointing the IDT at (unmapped_area + 
> vector), and deducing the vector in the page fault handler from cr2.

That would be still one byte, otherwise you wouldn't get a unique index.

-Andi

-- 
ak@...ux.intel.com
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