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Date: Sun, 22 Dec 2002 10:53:49 -0800 (PST)
From: Linus Torvalds <torvalds@transmeta.com>
To: Ingo Molnar <mingo@elte.hu>
cc: Jamie Lokier <lk@tantalophile.demon.co.uk>,
       Ulrich Drepper <drepper@redhat.com>, <bart@etpmod.phys.tue.nl>,
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Subject: Re: Intel P6 vs P7 system call performance
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On Sun, 22 Dec 2002, Ingo Molnar wrote:
>
> On Sat, 21 Dec 2002, Linus Torvalds wrote:
>
> > Saving and restoring eflags in user mode avoids all of these
> > complications, and means that there are no special cases. None. Zero.
> > Nada.
>
> and i'm 100% sure the more robust eflags saving will also avoid security
> holes. The amount of security-relevant complexity that comes from all the
> x86 features [and their combinations] is amazing.

I looked a bit at what it would take to have the TF bit handled by the
sysenter path, and it might not be so horrible - certainly not as ugly as
the register restore bits.

Jamie, if you want to do it, it looks like you could add a new "work" bit
in the thread flags, and add it to the _TIF_ALLWORK_MASK tests. At least
that way it wouldn't touch the regular code, and I don't think that the
result would have any strange "magic EIP" tests or anything horrible like
that ;)

		Linus

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