linux-kernel - Re: [PATCH 0/3] Remove interrupt stack table usage from x86

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Message-ID: <20081228190840.GD496@one.firstfloor.org>
Date:	Sun, 28 Dec 2008 20:08:40 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Avi Kivity <avi@...hat.com>
Cc:	Andi Kleen <andi@...stfloor.org>, x86@...nel.org,
	Ingo Molnar <mingo@...e.hu>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	KVM list <kvm@...r.kernel.org>
Subject: Re: [PATCH 0/3] Remove interrupt stack table usage from x86_64 kernel

On Sun, Dec 28, 2008 at 04:09:26PM +0200, Avi Kivity wrote:
> I don't see how syscall could work on i386, and indeed:

i386 has task gates which support unconditional stack switching. But there 
are no 64bit task gates, just ISTs.

BTW I think there are more similar problems in your patch too.

> 
> >vdso32.so-$(VDSO32-y)        += int80
> >vdso32.so-$(CONFIG_COMPAT)    += syscall
> >vdso32.so-$(VDSO32-y)        += sysenter
> 
> It's disabled.  Is that the reason?

No.  All interesting 32bit CPUs have SYSENTER; the only one who has SYSCALL 
but no SYSENTER is the K6, but it has a weird early variant of SYSCALL with
more problems which was never worth supporting.

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